Serve the format auto, chosen from the Accept header (closes #88)

auto is a format in the /v1/image/ path, an encrypted URL's token and
the generator page. Once the signature or token is checked, pixa
chooses AVIF when Accept names image/avif, else WebP when it names
image/webp, else JPEG when the most specific of image/jpeg, image/* and
*/* allows it or Accept is absent. q=0 refuses a format; a header
allowing none of the three answers 406, one that does not parse 400.
The signature and token cover auto itself; the cache key and ETag use
the chosen format. Answers from then on carry Vary: Accept.

Model: opus-5-5

.dockerignore

@@ -1,12 +1,73 @@
-# .git is sent without its config. Without a VERSION build argument the
-# stage that compiles runs `git describe --tags --always` on .git, which
-# does not need .git/config; that file can hold a credential, such as a
+# .dockerignore does NOT use .gitignore semantics. Docker matches with
+# moby/patternmatcher: filepath.Match plus `**`, so `*` does not cross
+# `/` and an unprefixed pattern is anchored at the context root. Every
+# depth-independent pattern therefore needs `**/`, or `config/.env` and
+# `certs/server.key` still ship while this file reads as solved. Only
+# genuinely root-anchored entries go unprefixed. Never transplant these
+# into .gitignore, where `**/` is wrong.
+#
+# Matching is case-sensitive, so secrets use character ranges rather
+# than an ALL-CAPS twin, which would still miss `Server.Key`.
+#
+# Extend with this repo's own host-built artifacts, written anchored:
+# `/myapp`, never `**/myapp`, which also matches `cmd/myapp/` and
+# deletes the package directory from the context.
+
+# Unlike the standard file, which leaves out all of .git, pixa sends
+# .git without its config. Without a VERSION build argument the stage
+# that compiles runs `git describe --tags --always` on .git, which does
+# not need .git/config; that file can hold a credential, such as a
 # password in a remote URL or the token the CI checkout step stores there.
 .git/config
-.gitignore
-.DS_Store
-.env*
+
+# Agent scratch: one full checkout of the repo per in-flight agent.
+# Anchored because it occurs once where agents run at the repo root.
+# KNOWN GAP: a repo running agents in subdirectories still ships
+# `services/api/.claude/` and must add its own anchored entry.
 .claude
-node_modules
-bin/
-data/
+
+# Environment files. `*.env` covers bare `.env` and the `prod.env`
+# convention. Re-include a committed template with a negation if the
+# build needs one: `!docs/example.env`.
+**/*.[eE][nN][vV]
+**/.[eE][nN][vV].*
+**/.[eE][nN][vV][rR][cC]
+
+# Private keys and the bundles carrying them. Public certificates
+# (*.crt, *.cer) are deliberately absent: they are legitimate inputs.
+**/*.[pP][eE][mM]
+**/*.[kK][eE][yY]
+**/*.[pP]12
+**/*.[pP][fF][xX]
+**/[iI][dD]_[rR][sS][aA]
+**/[iI][dD]_[dD][sS][aA]
+**/[iI][dD]_[eE][cC][dD][sS][aA]
+**/[iI][dD]_[eE][dD]25519
+
+# Dependencies: restored inside the image, never copied in.
+**/node_modules
+
+# OS metadata.
+**/.DS_Store
+**/Thumbs.db
+
+# Editor state: never a build input, and it churns COPY.
+**/*.swp
+**/*.swo
+**/*~
+**/*.bak
+**/.idea
+**/.vscode
+**/*.sublime-*
+
+# pixa's own entries. Nothing in the build reads .gitignore. On the
+# host, `make build` writes bin/pixad, and the example config keeps its
+# state directory in data/.
+.gitignore
+/bin
+/data
+
+# Local config files, kept out of git because they can hold the signing key.
+**/[cC][oO][nN][fF][iI][gG].[yY][mM][lL]
+**/[cC][oO][nN][fF][iI][gG].[yY][aA][mM][lL]
+**/[cC][oO][nN][fF][iI][gG].[dD][eE][vV].[yY][mM][lL]

.gitea/workflows/check.yml

@@ -6,5 +6,10 @@ jobs:
         steps:
             # actions/checkout v4.2.2, 2026-02-22
             - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+              # The default clone is shallow and has no tags, so the
+              # version the build takes from `git describe` would be a
+              # bare commit; this fetches the whole history with its tags.
+              with:
+                  fetch-depth: 0
             - run: script/cibuild
             - run: script/docker-smoke

.gitignore

@@ -11,6 +11,12 @@ Thumbs.db
 .vscode/
 *.sublime-*
 
+# Agent scratch (worktrees of this repo, created and destroyed by
+# in-flight tooling). Unanchored: .gitignore patterns already match at
+# every depth, so no prefix is wanted here. This is not a .dockerignore
+# entry and must not be given a `**/` prefix on the way into one.
+.claude/
+
 # Environment / secrets
 .env
 .env.*
@@ -31,5 +37,6 @@ node_modules/
 *.sqlite3
 
 # Local dev configs
+config.yml
 config.yaml
 config.dev.yml

.prettierignore

@@ -0,0 +1,7 @@
+node_modules/
+yarn.lock
+
+# A byte-for-byte copy of the one in sneak/prompts.
+REPO_POLICIES.md
+
+vendor/

.prettierrc

@@ -0,0 +1,4 @@
+{
+    "tabWidth": 4,
+    "proseWrap": "always"
+}

CLAUDE.md

@@ -4,73 +4,68 @@ Last Updated 2026-01-08
 
 These rules MUST be followed at all times, it is very important.
 
-* Never use `git add -A` - add specific changes to a deliberate commit. A
-  commit should contain one change. After each change, make a commit with a
-  good one-line summary.
+- Never use `git add -A` - add specific changes to a deliberate commit. A commit
+  should contain one change. After each change, make a commit with a good
+  one-line summary.
 
-* NEVER modify the linter config without asking first.
+- NEVER modify the linter config without asking first.
 
-* NEVER modify tests to exclude special cases or otherwise get them to pass
-  without asking first. In almost all cases, the code should be changed,
-  NOT the tests. If you think the test needs to be changed, make your case
-  for that and ask for permission to proceed, then stop. You need explicit
-  user approval to modify existing tests. (You do not need user approval
-  for writing NEW tests.)
+- NEVER modify tests to exclude special cases or otherwise get them to pass
+  without asking first. In almost all cases, the code should be changed, NOT the
+  tests. If you think the test needs to be changed, make your case for that and
+  ask for permission to proceed, then stop. You need explicit user approval to
+  modify existing tests. (You do not need user approval for writing NEW tests.)
 
-* When linting, assume the linter config is CORRECT, and that each item
-  output by the linter is something that legitimately needs fixing in the
-  code.
+- When linting, assume the linter config is CORRECT, and that each item output
+  by the linter is something that legitimately needs fixing in the code.
 
-* When running tests, use `make test`.
+- When running tests, use `make test`.
 
-* Before commits, run `make check`. This runs `make lint` and `make test`
-  and `make check-fmt`. Any issues discovered MUST be resolved before
-  committing unless explicitly told otherwise.
+- Before commits, run `make check`. This runs `make lint` and `make test` and
+  `make check-fmt`. Any issues discovered MUST be resolved before committing
+  unless explicitly told otherwise.
 
-* When fixing a bug, write a failing test for the bug FIRST. Add
-  appropriate logging to the test to ensure it is written correctly. Commit
-  that. Then go about fixing the bug until the test passes (without
-  modifying the test further). Then commit that.
+- When fixing a bug, write a failing test for the bug FIRST. Add appropriate
+  logging to the test to ensure it is written correctly. Commit that. Then go
+  about fixing the bug until the test passes (without modifying the test
+  further). Then commit that.
 
-* When adding a new feature, do the same - implement a test first (TDD). It
-  doesn't have to be super complex. Commit the test, then commit the
-  feature.
+- When adding a new feature, do the same - implement a test first (TDD). It
+  doesn't have to be super complex. Commit the test, then commit the feature.
 
-* When adding a new feature, use a feature branch. When the feature is
-  completely finished and the code is up to standards (passes `make check`)
-  then and only then can the feature branch be merged into `main` and the
-  branch deleted.
+- When adding a new feature, use a feature branch. When the feature is
+  completely finished and the code is up to standards (passes `make check`) then
+  and only then can the feature branch be merged into `main` and the branch
+  deleted.
 
-* Write godoc documentation comments for all exported types and functions as
-  you go along.
+- Write godoc documentation comments for all exported types and functions as you
+  go along.
 
-* ALWAYS be consistent in naming. If you name something one thing in one
-  place, name it the EXACT SAME THING in another place.
+- ALWAYS be consistent in naming. If you name something one thing in one place,
+  name it the EXACT SAME THING in another place.
 
-* Be descriptive and specific in naming. `wl` is bad;
-  `SourceHostWhitelist` is good. `ConnsPerHost` is bad;
-  `MaxConnectionsPerHost` is good.
+- Be descriptive and specific in naming. `wl` is bad; `SourceHostWhitelist` is
+  good. `ConnsPerHost` is bad; `MaxConnectionsPerHost` is good.
 
-* This is not prototype or teaching code - this is designed for production.
-  Any security issues (such as denial of service) or other web
-  vulnerabilities are P1 bugs and must be added to TODO.md at the top.
+- This is not prototype or teaching code - this is designed for production. Any
+  security issues (such as denial of service) or other web vulnerabilities are
+  P1 bugs and must be added to TODO.md at the top.
 
-* As this is production code, no stubbing of implementations unless
-  specifically instructed. We need working implementations.
+- As this is production code, no stubbing of implementations unless specifically
+  instructed. We need working implementations.
 
-* NEVER silently fall back to a different setting when a user's parameter
-  explicitly specifies a value. If a user requests format=webp and WebP
-  encoding is not supported, return an error - do NOT silently output PNG
-  instead. If a user specifies fit=invalid and that fit mode doesn't exist,
-  return an error - do NOT silently default to "cover". Silent fallbacks
-  violate the principle of least surprise and mask bugs. The only acceptable
-  defaults are for OMITTED parameters, never for INVALID explicit values.
+- NEVER silently fall back to a different setting when a user's parameter
+  explicitly specifies a value. If a user requests format=webp and WebP encoding
+  is not supported, return an error - do NOT silently output PNG instead. If a
+  user specifies fit=invalid and that fit mode doesn't exist, return an error -
+  do NOT silently default to "cover". Silent fallbacks violate the principle of
+  least surprise and mask bugs. The only acceptable defaults are for OMITTED
+  parameters, never for INVALID explicit values.
 
-* Avoid vendoring deps unless specifically instructed to.  NEVER commit
-  the vendor directory, NEVER commit compiled binaries.  If these
-  directories or files exist, add them to .gitignore (and commit the
-  .gitignore) if they are not already in there.  Keep the entire git
-  repository (with history) small - under 20MiB, unless you specifically
-  must commit larger files (e.g. test fixture example media files).  Only
-  OUR source code and immediately supporting files (such as test examples)
-  goes into the repo/history.
+- Avoid vendoring deps unless specifically instructed to. NEVER commit the
+  vendor directory, NEVER commit compiled binaries. If these directories or
+  files exist, add them to .gitignore (and commit the .gitignore) if they are
+  not already in there. Keep the entire git repository (with history) small -
+  under 20MiB, unless you specifically must commit larger files (e.g. test
+  fixture example media files). Only OUR source code and immediately supporting
+  files (such as test examples) goes into the repo/history.

Dockerfile

@@ -1,55 +1,62 @@
-# Lint stage
-# Same image as Dockerfile.lint: change both pins together.
-# golangci/golangci-lint:v2.12.2-alpine, 2026-08-07
-FROM golangci/golangci-lint:v2.12.2-alpine@sha256:91b27804074a0bacea298707f016911e60cf0cdbc6c7bf5ccacb5f0606d18d60 AS lint
+# Lint phase. script/lint builds it alone. The linter is run directly:
+# `make lint` and script/lint are themselves a docker build.
+# golangci/golangci-lint:v2.12.2, 2026-10-04
+FROM golangci/golangci-lint@sha256:5cceeef04e53efe1470638d4b4b4f5ceefd574955ab3941b2d9a68a8c9ad5240 AS lint
+
+# The linter compiles every package, and govips needs the libvips
+# headers for that. REPO_POLICIES.md has the lint phase install them
+# itself; this image is Debian, so with apt-get rather than apk.
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends libvips-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+RUN golangci-lint run --config .golangci.yml ./...
+
+# Test phase. script/test builds it alone.
+# golang:1.25.4-alpine, 2026-02-25
+FROM golang:1.25.4-alpine@sha256:d3f0cf7723f3429e3f9ed846243970b20a2de7bae6a5b66fc5914e228d831bbb AS test
 
 WORKDIR /src
 
-# script/bootstrap installs the build dependencies and downloads the Go
-# modules. Only script/, go.mod and go.sum are copied first, so this
-# layer is reused until one of them changes.
+# script/bootstrap --cgo installs the build dependencies (a C compiler
+# and the libvips and libheif headers) and downloads the Go modules.
 COPY script/ ./script/
 COPY go.mod go.sum ./
-RUN script/bootstrap
+RUN script/bootstrap --cgo
 
-# Copy source code
 COPY . .
 
-# Tells script/lint it is inside a container, so it runs the linter.
-ENV container=docker
+# Without -v first; on a failure, again with -v for the details, and
+# the step fails even if the second run passes.
+RUN go test -count=1 -timeout 90s -race -cover ./... || \
+    { echo "--- Rerunning with -v for details ---"; \
+      go test -count=1 -timeout 90s -race -v ./...; exit 1; }
 
-# Run formatting check and linter. script/cibuild and script/docker pass
-# a new CHECK_EPOCH on every run, and each check step names it in its
-# command, so a new value reruns the step instead of reusing a cached
-# success that checked nothing. A plain `docker build .` leaves it empty
-# and reuses the check steps only for an identical build context.
-ARG CHECK_EPOCH
-RUN echo "check epoch: ${CHECK_EPOCH}" && make fmt-check
-RUN echo "check epoch: ${CHECK_EPOCH}" && make lint
-
-# Build stage
+# Build stage. Nothing is wanted from the two phases above: these copies
+# make BuildKit build them first, so this stage runs only when lint and
+# test passed.
 # golang:1.25.4-alpine, 2026-02-25
 FROM golang:1.25.4-alpine@sha256:d3f0cf7723f3429e3f9ed846243970b20a2de7bae6a5b66fc5914e228d831bbb AS builder
 
-# Depend on lint stage passing
 COPY --from=lint /src/go.sum /dev/null
+COPY --from=test /src/go.sum /dev/null
 
 WORKDIR /src
 
-# Build dependencies and Go modules, as in the lint stage
+# Build dependencies and Go modules, as in the test phase
 COPY script/ ./script/
 COPY go.mod go.sum ./
-RUN script/bootstrap
+RUN script/bootstrap --cgo
 
 # Copy source code
 COPY . .
 
-# Run tests; a new CHECK_EPOCH reruns them, as in the lint stage.
-ARG CHECK_EPOCH
-RUN echo "check epoch: ${CHECK_EPOCH}" && make test
-
 # VERSION is declared here, not earlier: a new value reruns only the
-# build, not script/bootstrap or the tests. Given none, the version is
+# build, not script/bootstrap. Given none, the version is
 # `git describe --tags --always` of the .git in the build context (git
 # comes from script/bootstrap): the tag on a tagged commit, tag-N-gHASH
 # after one, the short commit when no tag is reachable. A context that
@@ -68,7 +75,8 @@ RUN version="${VERSION:-$(git describe --tags --always)}"; \
         -ldflags "-s -w -X main.Version=${version}" \
         -o /pixad ./cmd/pixad
 
-# Runtime stage
+# Runtime stage, and the last one: a plain `docker build .` builds this
+# stage and what it depends on, and nothing else.
 # alpine:3.21, 2026-02-25
 FROM alpine:3.21@sha256:c3f8e73fdb79deaebaa2037150150191b9dcbfba68b4a46d70103204c53f4709
 

Dockerfile.lint

@@ -1,34 +0,0 @@
-# Dockerfile.lint: the container script/lint builds to run golangci-lint,
-# which is never installed on the host. Pinned to the same image as the
-# Dockerfile lint stage: change both pins together, or the two run
-# different linter versions.
-#
-# golangci/golangci-lint:v2.12.2-alpine, 2026-08-07
-FROM golangci/golangci-lint:v2.12.2-alpine@sha256:91b27804074a0bacea298707f016911e60cf0cdbc6c7bf5ccacb5f0606d18d60
-
-WORKDIR /src
-
-# pixa is CGO/libvips: the type-aware linters compile every package, so
-# this image needs the same C libraries the build does. script/bootstrap
-# installs them and downloads the Go modules. Only script/, go.mod and
-# go.sum are copied first; they settle this layer's result, so it may
-# safely be reused between runs.
-COPY script/ ./script/
-COPY go.mod go.sum ./
-RUN script/bootstrap
-
-COPY . .
-
-# Tells script/lint it is inside a container, so it runs the linter.
-ENV container=docker
-
-# script/lint passes a different CACHEBUST on every run, and BuildKit
-# keys every RUN after this ARG on its value, so the lint step always
-# runs instead of returning a cached success that linted nothing.
-#
-# Go's and golangci-lint's caches (/root/.cache, hundreds of MB) go on a
-# tmpfs that is discarded after the step. Written into the layer, they
-# would pile up as build cache on every run, since no later run, with
-# its new CACHEBUST, can reuse that layer.
-ARG CACHEBUST
-RUN --mount=type=tmpfs,target=/root/.cache script/lint

Makefile

@@ -1,10 +1,10 @@
-.PHONY: bootstrap setup check lint test fmt fmt-check build clean docker docker-smoke docker-versioned docker-test devserver devserver-stop hooks
+.PHONY: bootstrap setup check lint test fmt fmt-check build clean docker docker-smoke docker-versioned docker-test devserver devserver-stop hooks loadtest
 
 VERSION := $(shell git describe --tags --always --dirty 2>/dev/null || echo "dev")
 LDFLAGS := -X main.Version=$(VERSION)
 
 # Use nix-shell to provide CGO dependencies unless they are already available
-# (e.g. inside a Docker build or an existing nix-shell).
+# (e.g. inside an existing nix-shell).
 HAS_PKGCONFIG := $(shell command -v pkg-config 2>/dev/null)
 ifdef HAS_PKGCONFIG
   NIX_RUN_PREFIX =
@@ -32,11 +32,11 @@ fmt-check:
 fmt:
 	@script/fmt
 
-# Run linter
+# Run linter (the lint phase of the Dockerfile)
 lint:
 	@script/lint
 
-# Run tests (30-second timeout)
+# Run tests (the test phase of the Dockerfile)
 test:
 	@script/test
 
@@ -59,20 +59,25 @@ docker:
 docker-smoke:
 	@script/docker-smoke
 
-# Build Docker image tagged pixad:$(VERSION) and pixad:latest
-docker-versioned:
-	docker build --build-arg VERSION=$(VERSION) -t pixad:$(VERSION) -t pixad:latest .
+# Measure throughput, latency and peak memory with the default duration and
+# number of clients (needs Docker and Go; a benchmark, not part of check)
+loadtest:
+	@script/loadtest
 
-# Run tests in Docker (needed for CGO/libvips)
+# Build Docker image as `make docker` does, and also tag it pixa:$(VERSION)
+docker-versioned:
+	@script/docker
+	docker tag pixa pixa:$(VERSION)
+
+# Run tests in Docker, as `make test` does
 docker-test:
-	docker build --target builder --build-arg VERSION=$(VERSION) -t pixad-builder .
-	docker run --rm pixad-builder sh -c "CGO_ENABLED=1 GOTOOLCHAIN=auto go test -v ./..."
+	@script/test
 
 # Run local dev server in Docker
 devserver: docker-versioned devserver-stop
 	docker run -d --name pixad-dev -p 8080:8080 \
 		-v $(CURDIR)/config.dev.yml:/etc/pixa/config.yml:ro \
-		pixad:latest
+		pixa:latest
 	@echo "pixad running at http://localhost:8080"
 
 # Stop dev server

README.md

@@ -1,10 +1,9 @@
 # pixa
 
-pixa is a GPL-3.0-licensed Go web server by
-[@sneak](https://sneak.berlin) that proxies images from upstream
-sources, optionally resizing or transforming them, and serves the
-results. Both source and transformed images are cached to disk so that
-subsequent requests are served without origin fetches or additional
+pixa is a GPL-3.0-licensed Go web server by [@sneak](https://sneak.berlin) that
+proxies images from upstream sources, optionally resizing or transforming them,
+and serves the results. Both source and transformed images are cached to disk so
+that subsequent requests are served without origin fetches or additional
 processing.
 
 ## Getting Started
@@ -27,12 +26,11 @@ make docker
 docker run -p 8080:8080 -e PIXA_SIGNING_KEY="$(openssl rand -base64 32)" pixa:latest
 ```
 
-A container takes its settings from environment variables (see
-Configuration below for the list). Only `PIXA_SIGNING_KEY` is required; if
-it is unset the container exits at startup naming the variable. Everything
-else has a built-in default. A config file mounted at `/etc/pixa/config.yml`
-is optional: it is read when present, and an environment variable wins over
-the same setting in it.
+A container takes its settings from environment variables (see Configuration
+below for the list). Only `PIXA_SIGNING_KEY` is required; if it is unset the
+container exits at startup naming the variable. Everything else has a built-in
+default. A config file mounted at `/etc/pixa/config.yml` is optional: it is read
+when present, and an environment variable wins over the same setting in it.
 
 ## Deployment
 
@@ -92,40 +90,42 @@ another part of pixa failed to stop. A request not finished by then is cut off.
 
 Outside Docker, pixa needs libvips (the image has 8.15) and libheif to run, as
 it uses libvips through CGO; building it also needs their development files,
-`pkg-config` and a C compiler. `script/bootstrap` installs all of these with
-nix, apt, brew or apk.
+`pkg-config` and a C compiler. `script/bootstrap --cgo` installs all of these,
+as the `Dockerfile` does where it compiles pixa. Plain `script/bootstrap`, which
+`script/setup` and `script/cibuild` run, installs git, make and Go, and Node,
+Yarn and the prettier pinned in `yarn.lock` for formatting the markdown, but
+none of the C libraries: the checks compile pixa in Docker. Docker itself must
+already be installed.
 
 ## Running under upaas
 
 What the [upaas](https://git.eeqj.de/sneak/upaas) app for pixa needs:
 
 - **Port:** pixa listens on container port `8080`.
-- **Volume:** container path `/var/lib/pixa`, where pixa keeps its
-  database and cache. Creating the host directory when it is missing is
-  upaas's job, tracked in https://git.eeqj.de/sneak/upaas/issues/235.
+- **Volume:** container path `/var/lib/pixa`, where pixa keeps its database and
+  cache. Creating the host directory when it is missing is upaas's job, tracked
+  in https://git.eeqj.de/sneak/upaas/issues/235.
 - **Environment variables:**
-    - `PIXA_SIGNING_KEY` (required): secret for signed and encrypted URLs
-      and login, 32+ characters, for example from
-      `openssl rand -base64 32`
+    - `PIXA_SIGNING_KEY` (required): secret for signed and encrypted URLs and
+      login, 32+ characters, for example from `openssl rand -base64 32`
     - `PIXA_ALLOWLIST_HOSTS`: upstream hosts served without a signature,
       comma-separated
     - `PIXA_CACHE_MAX_BYTES`: disk cache limit in bytes; `0` disables it;
       default 75% of (free space + what the cache holds)
     - the rest are in the table under Configuration below
 - **Health check:** the image's `HEALTHCHECK` requests
-  `/.well-known/healthcheck.json`. upaas reads the container's health 60
-  seconds after a deploy and marks the deploy failed unless it is
-  `healthy`. The probe uses the port from `PORT` (default `8080`), so a
-  port changed only in a mounted config file is not seen by it: change
-  the port with `PORT`.
+  `/.well-known/healthcheck.json`. upaas reads the container's health 60 seconds
+  after a deploy and marks the deploy failed unless it is `healthy`. The probe
+  uses the port from `PORT` (default `8080`), so a port changed only in a
+  mounted config file is not seen by it: change the port with `PORT`.
 
 ## Rationale
 
-Image-heavy web applications need a fast, caching reverse proxy that
-can resize and transcode images on the fly. pixa fills that role as a
-single, self-contained binary with no external runtime dependencies
-beyond libvips. It supports HMAC-SHA256 signed URLs with expiration to
-prevent abuse, and allowlisted source hosts for open access.
+Image-heavy web applications need a fast, caching reverse proxy that can resize
+and transcode images on the fly. pixa fills that role as a single,
+self-contained binary with no external runtime dependencies beyond libvips. It
+supports HMAC-SHA256 signed URLs with expiration to prevent abuse, and
+allowlisted source hosts for open access.
 
 ## Design
 
@@ -134,8 +134,8 @@ prevent abuse, and allowlisted source hosts for open access.
 - **Source content**:
   `<state_dir>/cache/sources/<ab>/<cd>/<sha256 of source content>`
 - **Source metadata**:
-  `<state_dir>/cache/metadata/<hostname>/<sha256 of path and query>.json`
-  (host, path and query, content hash, upstream status and headers, fetch time)
+  `<state_dir>/cache/metadata/<hostname>/<sha256 of path and query>.json` (host,
+  path and query, content hash, upstream status and headers, fetch time)
 - **Database**: `<state_dir>/state.sqlite3` (SQLite)
 - **Transformed images**:
   `<state_dir>/cache/variants/<ab>/<cd>/<sha256 of host, path, query, size, format, quality and fit>`,
@@ -144,12 +144,13 @@ prevent abuse, and allowlisted source hosts for open access.
 `<ab>` and `<cd>` are the first and second pairs of characters of the file's
 name.
 
-Multiple source paths may reference the same content blob; the
-database tracks references rather than using filesystem refcounting.
-Toward a target of 1-5k r/s, pixa keeps in memory the content types of
-the 10,000 transformed images most recently cached or served, so a
-cache hit on one of them reads only the image file from disk and not
-the metadata file stored beside it.
+Multiple source paths may reference the same content blob; the database tracks
+references rather than using filesystem refcounting.
+
+pixa's target is 1-5k r/s, which has not been measured at that rate (see Load
+Test). Toward it, pixa keeps in memory the content types of the 10,000
+transformed images most recently cached or served, so a cache hit on one of them
+reads only the image file from disk and not the metadata file stored beside it.
 
 ### Routes
 
@@ -159,8 +160,8 @@ answers any method as it answers `GET`. A browser's CORS preflight request
 (`OPTIONS` with `Origin` and `Access-Control-Request-Method` headers) to any
 path under `/v1/` answers 200, in maintenance mode too.
 
-- `GET /` — the login page, or the URL generator page with a login session
-  (see Encrypted URLs). Needs: nothing. Answers: 200.
+- `GET /` — the login page, or the URL generator page with a login session (see
+  Encrypted URLs). Needs: nothing. Answers: 200.
 - `POST /` — log in with the signing key typed into the login page. Needs: the
   login page's form (below). Answers: 303 to `/` with a login session cookie
   that lasts 30 days for the right key; 200 with the login page and an error for
@@ -174,12 +175,14 @@ path under `/v1/` answers 200, in maintenance mode too.
 - `GET` or `HEAD` `/v1/image/<host>/<path>/<size>.<format>` — an image, fetched,
   resized and converted (below). Needs: a signature, unless the host is
   allowlisted (see Source Hosts). Answers: 200; 304 when `If-None-Match` matches
-  the image's `ETag`; 400 for a URL or parameter that is not valid; 401 for a
-  missing or wrong signature, a missing `exp` or an `exp` in the past; 403 when
-  the request's `Referer` names a host in `referer_blocklist`, checked before
-  the signature, the cache and the upstream fetch; 403 when the upstream host,
-  or a host it redirects to, is `localhost`, ends in `.localhost` or `.local`,
-  or has an address in a blocked network (see `blocked_networks`); 502 when the
+  the image's `ETag`; 400 for a URL or parameter that is not valid, or for the
+  format `auto` an `Accept` header that is not valid; 406 for the format `auto`
+  when `Accept` allows none of the formats it chooses from; 401 for a missing or
+  wrong signature, a missing `exp` or an `exp` in the past; 403 when the
+  request's `Referer` names a host in `referer_blocklist`, checked before the
+  signature, the cache and the upstream fetch; 403 when the upstream host, or a
+  host it redirects to, is `localhost`, ends in `.localhost` or `.local`, or has
+  an address in a blocked network (see `blocked_networks`); 502 when the
   upstream answered with an error status, and for 5 minutes after that for the
   same source URL; 503 when pixa is busy or in maintenance mode; 500 for any
   other failure.
@@ -189,15 +192,15 @@ path under `/v1/` answers 200, in maintenance mode too.
   decrypt, or that asks for a size or fit that is not valid; 410 once it has
   expired; 504 when the upstream has not sent its response headers within
   `upstream_fetch_timeout`, but 500 when that time runs out while the image
-  itself is still arriving; 403, 502, 503 and 500 as for `/v1/image/`.
+  itself is still arriving; 400 for an `Accept` header that is not valid, and
+  406, 403, 502, 503 and 500, as for `/v1/image/`.
 - `GET /robots.txt` — asks every crawler to stay away (`Disallow: /`). Needs:
   nothing. Answers: 200.
 - `GET /.well-known/healthcheck.json` — JSON with `status` (`ok`), `now`,
-  `uptime_seconds`, `uptime_human`, `version`, `appname` and
-  `maintenance_mode`. Needs: nothing. Answers: 200, always.
-- `GET /static/<file>` — the stylesheet and script the login and generator
-  pages load. Needs: nothing. Answers: 200, or 404 for a file that does not
-  exist.
+  `uptime_seconds`, `uptime_human`, `version`, `appname` and `maintenance_mode`.
+  Needs: nothing. Answers: 200, always.
+- `GET /static/<file>` — the stylesheet and script the login and generator pages
+  load. Needs: nothing. Answers: 200, or 404 for a file that does not exist.
 - `GET /metrics` — Prometheus metrics (see Architecture). Needs: HTTP basic
   authentication with `metrics.username` and `metrics.password`. Answers: 200;
   401 without them; 404 when they are not set, as the route then does not exist.
@@ -221,9 +224,9 @@ HTTP is for development on the browser's own machine: the login session cookie
 is always marked `Secure`, and over plain HTTP a browser keeps such a cookie
 only for its own machine (`localhost`), if at all. A form is also refused with
 403 when the page's host is not the `Host` header pixa receives, so a reverse
-proxy in front of pixa must pass that header on unchanged. A form body over
-1 MiB is refused with 413. The image routes answer the errors listed for them
-with JSON holding `error`, `status` and `timestamp`.
+proxy in front of pixa must pass that header on unchanged. A form body over 1
+MiB is refused with 413. The image routes answer the errors listed for them with
+JSON holding `error`, `status` and `timestamp`.
 
 An image URL has this form:
 
@@ -235,48 +238,64 @@ Images are only fetched from origins using TLS with valid certificates, unless
 `allow_http` is set: then pixa fetches every image over plain HTTP, which is for
 testing only.
 
-A request whose query string cannot be decoded, or gives any parameter more
-than once, is refused with 400.
+A request whose query string cannot be decoded, or gives any parameter more than
+once, is refused with 400.
 
 - `<format>`: one of `orig` (or `original`), `jpeg` (or `jpg`), `png`, `webp`,
-  `avif`, `gif`
+  `avif`, `gif`, or `auto` (below)
 - `<size>`: `orig` or `<width>x<height>` (e.g. `800x600`)
 - `sig` and `exp`: the signature and its expiry, needed unless the host is
   allowlisted (see Signature Specification)
 - `q` and `fit`: the output quality and how the image is fitted to `<size>`,
-  both optional (values under Signature Specification). Both are part of what
-  is cached, so each value of either is a separate cached image.
+  both optional (values under Signature Specification). Both are part of what is
+  cached, so each value of either is a separate cached image.
+
+With the format `auto`, pixa chooses the format for each request from its
+`Accept` header, in this order:
+
+1. AVIF, when the header names `image/avif`;
+2. WebP, when it names `image/webp`;
+3. JPEG, when the first of `image/jpeg`, `image/*` and `*/*` that it names
+   allows it, or when there is no `Accept` header or it is empty.
+
+An entry with `q=0` refuses its format; other `q` values do not change the
+order. AVIF and WebP must be named, as clients that cannot show them also send
+`image/*` and `*/*`. pixa never sends a format the client refused: when the
+header allows none of the three, the answer is 406, and a header that does not
+parse, or has a `q` that is not a number from 0 to 1, is refused with 400. The
+signature, or the token of an encrypted URL, covers `auto` itself, so one URL
+serves every client. Each format chosen is cached as a separate image, and every
+answer that depends on `Accept` (the image, a 304, and the 400 and 406 above)
+carries `Vary: Accept`, so a shared cache keeps the formats apart too.
 
 An image is served with `Cache-Control: public, max-age=<seconds>, immutable`.
-When the URL has an expiry (an `exp`, or the TTL of an encrypted URL),
-`max-age` is the whole seconds left until then, at most one year, so no browser
-or proxy cache keeps the image after pixa would refuse the URL. A URL with no
-expiry gets one year. `immutable` only stops a client revalidating while its
-copy is fresh.
+When the URL has an expiry (an `exp`, or the TTL of an encrypted URL), `max-age`
+is the whole seconds left until then, at most one year, so no browser or proxy
+cache keeps the image after pixa would refuse the URL. A URL with no expiry gets
+one year. `immutable` only stops a client revalidating while its copy is fresh.
 
-When several requests for the same image, size, format, quality and fit miss
-the cache at once, they share one upstream fetch (or one read of the cached
-source) and one transcode: the first request does the work, and the others wait
-for its image or its error, holding no upstream connection or processing slot
-of their own. A waiting request stops waiting when its own client goes away.
-The work goes on for the others even if the first request's client goes away,
-until that request's `downstream_timeout` ends. The shared fetch sends the first
-request's ID upstream, and the lines logged for the fetch and the transcode
-carry that ID.
+When several requests for the same image, size, format, quality and fit miss the
+cache at once, they share one upstream fetch (or one read of the cached source)
+and one transcode: the first request does the work, and the others wait for its
+image or its error, holding no upstream connection or processing slot of their
+own. A waiting request stops waiting when its own client goes away. The work
+goes on for the others even if the first request's client goes away, until that
+request's `downstream_timeout` ends. The shared fetch sends the first request's
+ID upstream, and the lines logged for the fetch and the transcode carry that ID.
 
 The login form (`POST /`) is limited to 5 attempts per minute per client
 address, counting an IPv6 client by its /64; an attempt over the limit is
 refused with 429 and a `Retry-After` header. Behind a reverse proxy the client
 address comes from `X-Forwarded-For` only when the address pixa sees for
 requests that come through the proxy is in `trusted_proxies`; otherwise all
-users behind the proxy are counted as one client. That address is not always
-the proxy's own: a proxy on the Docker host that connects to pixa over
-`127.0.0.1` is seen as the gateway of the container's Docker network, such as
-`172.17.0.1` on the default bridge, and one that connects through another of the
-host's addresses is seen with that address. To be sure, read it as `remoteIP` in
-pixa's request log while it is not in `trusted_proxies` (see `trusted_proxies`
-under Configuration). With the default `trusted_proxies` (the RFC 1918 ranges),
-a client with a private address can choose the address it is counted by through
+users behind the proxy are counted as one client. That address is not always the
+proxy's own: a proxy on the Docker host that connects to pixa over `127.0.0.1`
+is seen as the gateway of the container's Docker network, such as `172.17.0.1`
+on the default bridge, and one that connects through another of the host's
+addresses is seen with that address. To be sure, read it as `remoteIP` in pixa's
+request log while it is not in `trusted_proxies` (see `trusted_proxies` under
+Configuration). With the default `trusted_proxies` (the RFC 1918 ranges), a
+client with a private address can choose the address it is counted by through
 its own `X-Forwarded-For`, whether it connects directly or through the proxy,
 because its own address is trusted too. Setting `trusted_proxies` to only the
 address pixa sees for requests that come through the proxy closes this.
@@ -299,20 +318,20 @@ nor change what it asks for.
 3. The page shows the URL, `https://<host>/v1/e/<token>/img.<format>`, and when
    it expires. `<host>` is the host the page was opened on, and the URL starts
    with `http` instead while `debug` is on. The name after the token is ignored
-   and only gives the URL a file extension, `jpg` for `orig`.
+   and only gives the URL a file extension, `jpg` for `orig` and `auto`.
 
-The token holds the source's host, path and query and the size, format,
-quality, fit and expiry, encrypted with a key derived from `signing_key`. The
-source URL's scheme is not kept: the image is fetched like any other (see
-Routes), and the blocked networks still apply.
+The token holds the source's host, path and query and the size, format, quality,
+fit and expiry, encrypted with a key derived from `signing_key`. The source
+URL's scheme is not kept: the image is fetched like any other (see Routes), and
+the blocked networks still apply.
 
-How long the URL lasts is chosen on the page, from 1 minute to 1 year, or
-never. The expiry is fixed in the token when the URL is made and cannot be
-changed or revoked afterwards. Until then the image is served with a `max-age`
-that ends at the expiry (see Routes); after it the URL answers 410
-`URL has expired`. A URL made to last forever stops working only when
-`signing_key` changes: changing it makes every encrypted URL already handed out
-answer 400, and ends every login session.
+How long the URL lasts is chosen on the page, from 1 minute to 1 year, or never.
+The expiry is fixed in the token when the URL is made and cannot be changed or
+revoked afterwards. Until then the image is served with a `max-age` that ends at
+the expiry (see Routes); after it the URL answers 410 `URL has expired`. A URL
+made to last forever stops working only when `signing_key` changes: changing it
+makes every encrypted URL already handed out answer 400, and ends every login
+session.
 
 ### Image Metadata
 
@@ -331,16 +350,15 @@ turned off.
 
 ### Source Hosts
 
-Source hosts may be allowlisted in the configuration. Non-allowlisted
-hosts require an HMAC-SHA256 signature.
+Source hosts may be allowlisted in the configuration. Non-allowlisted hosts
+require an HMAC-SHA256 signature.
 
 #### Signature Specification
 
-Signatures use HMAC-SHA256 and include an expiration timestamp to
-prevent replay attacks. Signatures are **exact match only**: every
-component (host, path, query, dimensions, format, expiration, quality,
-fit) must match exactly what was signed. No suffix matching, wildcard
-matching, or partial matching is supported.
+Signatures use HMAC-SHA256 and include an expiration timestamp to prevent replay
+attacks. Signatures are **exact match only**: every component (host, path,
+query, dimensions, format, expiration, quality, fit) must match exactly what was
+signed. No suffix matching, wildcard matching, or partial matching is supported.
 
 **Signed data format** (colon-separated):
 
@@ -356,25 +374,26 @@ Where:
 - `width` — requested width in pixels, `0` for original
 - `height` — requested height in pixels, `0` for original
 - `format` — output format, one of those listed under Routes, with `original`
-  signed as `orig` and `jpg` as `jpeg`
-- `expiration` — the URL's `exp` query parameter, the Unix timestamp when
-  the signature expires; a request whose `exp` is not a whole number, an
-  empty `exp=` included, is refused with 400
-- `quality` — the URL's `q` query parameter, a whole number from 1 to 100,
-  or `85` when the URL has no `q`; a request whose `q` is anything else is
-  refused with 400
+  signed as `orig` and `jpg` as `jpeg`; `auto` is signed as `auto`, not as the
+  format chosen for the request
+- `expiration` — the URL's `exp` query parameter, the Unix timestamp when the
+  signature expires; a request whose `exp` is not a whole number, an empty
+  `exp=` included, is refused with 400
+- `quality` — the URL's `q` query parameter, a whole number from 1 to 100, or
+  `85` when the URL has no `q`; a request whose `q` is anything else is refused
+  with 400
 - `fit` — the URL's `fit` query parameter (cover, contain, fill, inside,
   outside), or `cover` when the URL has no `fit`; a request whose `fit` is
   anything else, an empty `fit=` included, is refused with 400
 
-The URL's `sig` is the HMAC-SHA256 result in base64url (the URL-safe alphabet
-of RFC 4648) with the trailing `=` padding kept, 44 characters in all. pixa
+The URL's `sig` is the HMAC-SHA256 result in base64url (the URL-safe alphabet of
+RFC 4648) with the trailing `=` padding kept, 44 characters in all. pixa
 compares it exactly, so a signature encoded without padding, as Node's
 `base64url` and Go's `base64.RawURLEncoding` do, is refused with 401.
 
 **Example:** with the signing key `example-signing-key-for-documentation`,
-resize `https://cdn.example.com/photos/cat.jpg` to 800x600 WebP with
-expiration 1704067200, default quality and fit:
+resize `https://cdn.example.com/photos/cat.jpg` to 800x600 WebP with expiration
+1704067200, default quality and fit:
 
 1. Build input:
    `cdn.example.com:/photos/cat.jpg::800:600:webp:1704067200:85:cover`
@@ -402,29 +421,29 @@ or a `*.` wildcard, aborts startup.
 
 ### Configuration
 
-Every setting can be given as an environment variable, in a YAML config
-file (`--config`), or both. A variable present in the environment wins over
-the file, even when it is empty, and the file wins over the built-in
-default. The one exception is a variable named in the file's `env:` section:
-it is set while the file loads, so it overrides both the environment the
-process was started with and the file's own key. A variable's value is
-parsed as the same text in the file would be. The three lists take
-comma-separated entries, with the spaces around each trimmed; an empty
-variable is an empty list. A value that does not parse or is invalid aborts
-startup, naming the variable. A variable whose name starts with `PIXA_` but
-is not in the table below, such as a misspelled one or `PIXA_PORT`, aborts
-startup naming it, as an unknown config key does. The one other accepted
-name is `PIXA_CONFIG_PATH`, the config file's path (like `--config`). The
-variables set by the file's `env:` section are checked the same way.
+Every setting can be given as an environment variable, in a YAML config file
+(`--config`), or both. A variable present in the environment wins over the file,
+even when it is empty, and the file wins over the built-in default. The one
+exception is a variable named in the file's `env:` section: it is set while the
+file loads, so it overrides both the environment the process was started with
+and the file's own key. A variable's value is parsed as the same text in the
+file would be. The three lists take comma-separated entries, with the spaces
+around each trimmed; an empty variable is an empty list. A value that does not
+parse or is invalid aborts startup, naming the variable. A variable whose name
+starts with `PIXA_` but is not in the table below, such as a misspelled one or
+`PIXA_PORT`, aborts startup naming it, as an unknown config key does. The one
+other accepted name is `PIXA_CONFIG_PATH`, the config file's path (like
+`--config`). The variables set by the file's `env:` section are checked the same
+way.
 
 pixa reads at most one config file: the one given with `--config` (or `-c`),
 otherwise the one `PIXA_CONFIG_PATH` names, otherwise the first of these that
 pixa finds: `/etc/pixa/config.yml`, `/etc/pixa/config.yaml`,
-`~/.config/pixa/config.yml`, `~/.config/pixa/config.yaml`, then `config.yml`
-and `config.yaml` in the working directory. A named file that does not exist,
-cannot be read or does not parse aborts startup. Of the files pixa looks for on
-its own, only one that does not exist is passed over, without a message. One
-that pixa cannot read or parse aborts startup, naming the file. So does one in a
+`~/.config/pixa/config.yml`, `~/.config/pixa/config.yaml`, then `config.yml` and
+`config.yaml` in the working directory. A named file that does not exist, cannot
+be read or does not parse aborts startup. Of the files pixa looks for on its
+own, only one that does not exist is passed over, without a message. One that
+pixa cannot read or parse aborts startup, naming the file. So does one in a
 directory pixa may not enter, whether or not it is there, since pixa cannot
 tell. With no file, pixa uses the environment and the defaults.
 
@@ -459,11 +478,11 @@ Key settings in more detail:
   of the image routes, `/v1/image/` and `/v1/e/`, sent as the CORS
   `Access-Control-Allow-Origin` header; no other route sends it. `*`, the
   default, is any site; otherwise one `http` or `https` origin such as
-  `https://example.com`, whose host is a lowercase host name (letters,
-  digits, hyphens and dots, with a letter in its last part) or an IP address
-  (IPv6 in brackets, in its shortest form), with an optional port 1-65535
-  that has no leading zero and is not the scheme's default. Any other value,
-  including another scheme such as a browser extension's, aborts startup
+  `https://example.com`, whose host is a lowercase host name (letters, digits,
+  hyphens and dots, with a letter in its last part) or an IP address (IPv6 in
+  brackets, in its shortest form), with an optional port 1-65535 that has no
+  leading zero and is not the scheme's default. Any other value, including
+  another scheme such as a browser extension's, aborts startup
 - `allowlist_hosts` — list of allowed upstream hosts
 - `referer_blocklist` — list of hosts whose pages may not show pixa's images, to
   stop other sites hotlinking them. Entries are written and matched as for
@@ -472,40 +491,37 @@ Key settings in more detail:
   `/v1/e/` whose `Referer` header names a listed host is refused with 403 before
   its signature or token is checked and before the cache or the upstream host is
   used, so it fetches nothing, and it is refused even when the image is cached.
-  A request with no `Referer`, or one that does not parse as a URL
-  with a host, is served, as many clients send none. So this is easily got
-  around: a site whose pages send no `Referer` (for example with
+  A request with no `Referer`, or one that does not parse as a URL with a host,
+  is served, as many clients send none. So this is easily got around: a site
+  whose pages send no `Referer` (for example with
   `Referrer-Policy: no-referrer`) is not stopped. It does not apply to the login
   and generator pages. Default: empty
-- `blocked_networks` — list of CIDR ranges to refuse for SSRF protection,
-  added to the always-enforced built-in ranges (loopback, private,
-  link-local, CGNAT, benchmark, NAT64, and the like); an invalid CIDR
-  aborts startup
-- `trusted_proxies` — list of CIDR ranges of the reverse proxies in front
-  of pixa. `X-Forwarded-For` is believed only when the direct peer falls
-  inside one of these ranges; the logged and login-recorded client
-  address is then the rightmost forwarded entry that is not itself a
-  trusted proxy. Otherwise the direct peer address is used and the header
-  is ignored, so a client connecting directly from an address outside
-  these ranges cannot spoof its address.
-  An omitted key defaults to the RFC 1918 private ranges (`10.0.0.0/8`,
-  `172.16.0.0/12`, `192.168.0.0/16`), since pixa is deployed behind a
-  proxy on a private network; an explicitly empty list (`[]`) trusts no
-  one, and an explicit list replaces the default. An invalid CIDR aborts
-  startup. Set this to the address pixa sees for requests that come through
-  your proxy, such as `172.17.0.1/32`, when the defaults do not cover it, or
-  to trust nothing else (see the login limit under Routes). For a proxy on
-  the Docker host that connects to pixa over `127.0.0.1`, that address is the
-  gateway of the container's Docker network (`172.17.0.1` on the default
-  bridge), not the proxy's own address; a proxy that connects through another of
-  the host's addresses is seen with that address. To be sure which address it
-  is, set this to `[]` (or `PIXA_TRUSTED_PROXIES` to empty), send a request
-  through the proxy, and read `remoteIP` in pixa's request log line for it
-- `upstream_fetch_timeout` — time allowed for one fetch from an upstream
-  host, as a duration such as `30s` (the default) or `2m`
-- `upstream_max_response_size` — largest upstream response accepted, in
-  bytes; default `52428800` (50 MiB). It also limits the image data pixa
-  decodes
+- `blocked_networks` — list of CIDR ranges to refuse for SSRF protection, added
+  to the always-enforced built-in ranges (loopback, private, link-local, CGNAT,
+  benchmark, NAT64, and the like); an invalid CIDR aborts startup
+- `trusted_proxies` — list of CIDR ranges of the reverse proxies in front of
+  pixa. `X-Forwarded-For` is believed only when the direct peer falls inside one
+  of these ranges; the logged and login-recorded client address is then the
+  rightmost forwarded entry that is not itself a trusted proxy. Otherwise the
+  direct peer address is used and the header is ignored, so a client connecting
+  directly from an address outside these ranges cannot spoof its address. An
+  omitted key defaults to the RFC 1918 private ranges (`10.0.0.0/8`,
+  `172.16.0.0/12`, `192.168.0.0/16`), since pixa is deployed behind a proxy on a
+  private network; an explicitly empty list (`[]`) trusts no one, and an
+  explicit list replaces the default. An invalid CIDR aborts startup. Set this
+  to the address pixa sees for requests that come through your proxy, such as
+  `172.17.0.1/32`, when the defaults do not cover it, or to trust nothing else
+  (see the login limit under Routes). For a proxy on the Docker host that
+  connects to pixa over `127.0.0.1`, that address is the gateway of the
+  container's Docker network (`172.17.0.1` on the default bridge), not the
+  proxy's own address; a proxy that connects through another of the host's
+  addresses is seen with that address. To be sure which address it is, set this
+  to `[]` (or `PIXA_TRUSTED_PROXIES` to empty), send a request through the
+  proxy, and read `remoteIP` in pixa's request log line for it
+- `upstream_fetch_timeout` — time allowed for one fetch from an upstream host,
+  as a duration such as `30s` (the default) or `2m`
+- `upstream_max_response_size` — largest upstream response accepted, in bytes;
+  default `52428800` (50 MiB). It also limits the image data pixa decodes
 - `downstream_timeout` — time allowed for answering one client request, as a
   duration; default `60s`. The upstream fetch counts toward it, and so do the
   waits for an upstream connection and for a processing slot (up to 10 seconds
@@ -517,11 +533,11 @@ Key settings in more detail:
   so a write that finds another in progress waits up to five seconds for it
   instead of failing. WAL mode comes only from the URL: keep
   `_pragma=journal_mode(WAL)` in one you set
-- `cache_max_bytes` — disk cache size limit in bytes; `0` disables the
-  disk cache entirely; omitted defaults to 75% of the sum of the free space on
-  the filesystem containing `<state_dir>/cache/` and the bytes of source and
-  transformed images the cache already holds, worked out at startup (minimum
-  500 MiB)
+- `cache_max_bytes` — disk cache size limit in bytes; `0` disables the disk
+  cache entirely; omitted defaults to 75% of the sum of the free space on the
+  filesystem containing `<state_dir>/cache/` and the bytes of source and
+  transformed images the cache already holds, worked out at startup (minimum 500
+  MiB)
 - `upstream_connections` — the most connections to upstream hosts at once, all
   hosts together, on top of `upstream_connections_per_host`; default `64`. A
   fetch holds its connection until its image has been processed. A fetch that
@@ -536,10 +552,10 @@ Key settings in more detail:
 - `maintenance_mode` — while `true`, the image routes (`/v1/image/` and
   `/v1/e/`) answer every request for an image with 503, a `Retry-After` header
   and a JSON error body. The health check (`/.well-known/healthcheck.json`)
-  still answers 200 and reports `"maintenance_mode": true`. It stays 200
-  because the image's Docker `HEALTHCHECK` requests it: a 503 there would make
-  the container unhealthy, and upaas marks a deploy failed when its container
-  is unhealthy. The login and URL generator pages and `/metrics` keep working
+  still answers 200 and reports `"maintenance_mode": true`. It stays 200 because
+  the image's Docker `HEALTHCHECK` requests it: a 503 there would make the
+  container unhealthy, and upaas marks a deploy failed when its container is
+  unhealthy. The login and URL generator pages and `/metrics` keep working
 
 See `configs/config.example.yml` for all options with defaults.
 
@@ -561,28 +577,98 @@ See `configs/config.example.yml` for all options with defaults.
 This repository adheres to the
 [Scripts to Rule Them All](https://github.com/github/scripts-to-rule-them-all)
 standard: normalized scripts in `script/` are the entrypoints for the
-development workflow, and the Makefile targets are thin shims that call
-them. We provide:
+development workflow, and the Makefile targets are thin shims that call them. We
+provide:
 
-- `script/bootstrap` — install all dependencies (idempotent)
-- `script/setup` — make a fresh clone ready for development
-  (bootstrap, then install-precommit)
+- `script/bootstrap` — install git, make, Go, Node, Yarn and prettier and
+  download the Go modules (idempotent); with `--cgo`, the C compiler and the
+  libvips and libheif libraries that compiling pixa needs instead of Node, Yarn
+  and prettier
+- `script/setup` — make a fresh clone ready for development (bootstrap, then
+  install-precommit)
 - `script/projectname` — output the project name ("pixa")
-- `script/test` — run the test suite
-- `script/lint` — run golangci-lint, always in a container (builds
-  `Dockerfile.lint` when run outside one)
-- `script/fmt` — format all code (writes)
-- `script/fmt-check` — check formatting (read-only)
+- `script/test` — run the test suite: build the `test` phase of the
+  `Dockerfile`, tagged `pixa-test`
+- `script/lint` — run golangci-lint: build the `lint` phase of the `Dockerfile`,
+  tagged `pixa-lint`; the linter never runs on the host
+- `script/fmt` — format the Go code with gofmt and the markdown with prettier
+  (writes)
+- `script/fmt-check` — check the same formatting (read-only), on the host
 - `script/check` — run test, lint, and fmt-check
-- `script/docker` — build the Docker image tagged via `script/projectname`
+- `script/docker` — build the Docker image tagged via `script/projectname`, with
+  the version from `git describe`; the image's build stage depends on the `lint`
+  and `test` phases, so this runs them too
 - `script/docker-smoke` — build the image, start it, wait for it to be healthy
-- `script/cibuild` — CI entrypoint: `docker build .` with a new
-  `CHECK_EPOCH` on every run, so the Dockerfile's checks run instead of
-  coming from the build cache, and a green run implies a green repo
+- `script/loadtest` — measure pixad's throughput, latency and peak memory; a
+  benchmark, not part of `script/check` (see Load Test)
+- `script/cibuild` — CI entrypoint: run `script/bootstrap` (without `--cgo`),
+  then `script/check`, then build the image as `script/docker` does
 - `script/precommit` — pre-commit checks (`go mod tidy` guard, then
   `script/check`)
-- `script/install-precommit` — install the git pre-commit hook that
-  runs `script/precommit`
+- `script/install-precommit` — install the git pre-commit hook that runs
+  `script/precommit`
+
+Every `docker build` in these scripts passes `--no-cache`, so the lint and test
+phases run on every build instead of coming from the build cache.
+`script/check`, `script/cibuild`, `script/docker`, `script/lint`, `script/test`,
+`script/setup` and `script/install-precommit` are the standard copies from
+`sneak/prompts`, kept identical to them. `script/fmt` and `script/fmt-check` are
+the standard copies with pixa's `gofmt` step kept before prettier. prettier
+formats the markdown only: not the HTML templates, as it cannot parse a Go
+template action inside a tag, and not `REPO_POLICIES.md` (see
+`.prettierignore`), a copy of the one in `sneak/prompts`.
+
+## Load Test
+
+`script/loadtest` (or `make loadtest`) measures how fast pixad answers and how
+much memory it uses. It is a benchmark, not a check: `script/check` does not run
+it. It needs Docker and Go.
+
+```bash
+script/loadtest           # 10 seconds per scenario, 4 clients
+script/loadtest 30s 32    # 30 seconds per scenario, 32 clients
+```
+
+It builds the image with `script/docker` and the load tool,
+[vegeta](https://github.com/tsenart/vegeta), from a pinned commit. Each scenario
+starts a new pixad container and a new origin container, `cmd/loadtest-origin`:
+an upstream host that answers every path with the same generated 1600x1200 JPEG.
+vegeta then sends requests from the given number of clients, each sending its
+next request as soon as its last one is answered, all for an image resized to
+400x300 WebP:
+
+- `hit`: the same image every time, put in the cache first;
+- `miss`: a new source image every time, so pixad fetches and converts each one;
+- `herd`: each new source image once per client in a row, so that all clients
+  ask for it at the same time and share one fetch and one conversion (see
+  Routes).
+
+pixad refuses upstream hosts with private or local addresses, so the containers
+share a Docker network in `203.0.113.0/24`, a range set aside for documentation.
+A second run on the same Docker host while one is going fails, as it cannot
+create that network.
+
+For each scenario the script prints vegeta's report and two lines of its own:
+
+- `Requests [total, rate, throughput]`: the requests sent, how many were sent
+  per second, and how many were answered successfully per second; the last is
+  the number to compare with the target under Storage;
+- `Latencies [min, mean, 50, 90, 95, 99, max]`: the time from sending a request
+  to the end of its answer; `50`, `95` and `99` are the 50th, 95th and 99th
+  percentiles;
+- `Status Codes` and `Error Set`: anything other than `200` means the other
+  numbers are not for the scenario described, such as `503` when pixad was busy;
+- `Bytes In`: `0`, as vegeta is told not to keep the images it receives;
+- `pixad peak memory (VmHWM)`: the peak resident memory of pixad's process since
+  its container started, in kB; for `hit` it includes the request that put the
+  image in the cache;
+- `requests to the origin`: the fetches pixad made: one for `hit`, one per
+  request for `miss`, and one per image for `herd`, that is the requests sent
+  divided by the number of clients.
+
+The numbers depend on the machine and on whatever else runs on it. The first
+measurement, made on a shared machine with few clients, is in `TODO.md`; it says
+nothing about the target.
 
 ## TODO
 

REPO_POLICIES.md

@@ -1,6 +1,6 @@
 ---
 title: Repository Policies
-last_modified: 2026-07-06
+last_modified: 2026-09-08
 ---
 
 This document covers repository structure, tooling, and workflow standards. Code
@@ -60,17 +60,28 @@ style conventions are in separate documents:
   prerequisite since nvm requires bash. yarn is then pinned via
   `corepack prepare yarn@<version> --activate`. Never install "latest" or "lts";
   always exact versions. `script/cibuild` runs the CI build: it changes to the
-  repo root and runs `docker build .`; the Gitea workflow calls it. Four further
-  scripts are our own extensions to the standard: `script/check` runs
-  `script/test`, `script/lint`, and `script/fmt-check`; `script/precommit` is
-  what the git pre-commit hook runs, and it calls `script/check`;
-  `script/install-precommit` installs the git pre-commit hook (the `make hooks`
-  target shims to it); and `script/projectname` (literally that filename) simply
-  outputs the project's name. Scripts that need the name call
-  `script/projectname` — e.g. `script/docker` assembles its image tag from it —
-  so those scripts stay byte-identical across all repos. Repo-type-specific
-  pre-commit extras (e.g. `go mod tidy` verification in Go repos) belong in
-  `script/precommit`, not in the hook itself. Model scripts are at
+  repo root, runs `script/bootstrap`, runs `script/check`, and builds the image
+  with the version; the Gitea workflow calls it. **`script/cibuild` runs
+  `script/bootstrap` first**, because the workflow checks out the repo and runs
+  nothing else, while `script/fmt-check` runs the formatter on the host: on a
+  pristine checkout with nothing installed the run dies there, after the
+  containerised gates have passed. **The bootstrap alone is not enough**:
+  `script/bootstrap` installs node and yarn under nvm and leaves neither on the
+  `PATH` of the shell that called it, so a bare `yarn` still exits 127. The host
+  entrypoints that need yarn — `script/fmt` and `script/fmt-check` — therefore
+  source nvm for the pinned node version before invoking it, exactly as
+  `script/bootstrap`'s own install step does. A runner carrying nothing but
+  docker and git then gets through `script/check`. Four further scripts are our
+  own extensions to the standard: `script/check` runs `script/test`,
+  `script/lint` and `script/fmt-check`; `script/precommit` is what the git
+  pre-commit hook runs, and it calls `script/check`; `script/install-precommit`
+  installs the git pre-commit hook (the `make hooks` target shims to it); and
+  `script/projectname` (literally that filename) simply outputs the project's
+  name. Scripts that need the name call `script/projectname` — e.g.
+  `script/docker` assembles its image tag from it — so those scripts stay
+  byte-identical across all repos. Repo-type-specific pre-commit extras (e.g.
+  `go mod tidy` verification in Go repos) belong in `script/precommit`, not in
+  the hook itself. Model scripts are at
   `https://git.eeqj.de/sneak/prompts/raw/branch/main/script/<name>`. The README
   must document the provided scripts in an **Entrypoints** section (see the
   README requirements below).
@@ -89,87 +100,140 @@ style conventions are in separate documents:
   contributor should be able to understand the entire development workflow by
   reading the Makefile.
 
-- Every repo should have a `Dockerfile`. All Dockerfiles must run `make check`
-  as a build step so the build fails if the branch is not green. For non-server
-  repos, the Dockerfile should bring up a development environment and run
-  `make check`. For server repos, `make check` should run as an early build
-  stage before the final image is assembled. Dockerfiles install development
-  prerequisites by running `script/bootstrap` rather than duplicating installs
-  inline; COPY `script/` and the dependency manifests (`package.json` +
-  `yarn.lock`, `go.mod` + `go.sum`, etc.) before running it so the bootstrap
-  layer stays cached until dependencies change.
+- Every repo should have a `Dockerfile`, and it carries the repo's gates: a
+  `lint` phase and a `test` phase, with the final stage depending on both so the
+  image cannot be built unless they pass. For non-server repos the final stage
+  brings up a development environment; for server repos it is the runtime image.
+  Dockerfiles install development prerequisites by running `script/bootstrap`
+  rather than duplicating installs inline; COPY `script/` and the dependency
+  manifests (`package.json` + `yarn.lock`, `go.mod` + `go.sum`, etc.) before
+  running it.
 
-- **Dockerfiles must use a separate lint stage for fail-fast feedback.** Go
-  repos use a multistage build where linting runs in an independent stage based
-  on the `golangci/golangci-lint` image (pinned by hash). This stage runs
-  `make fmt-check` and `make lint` before the full build begins. The build stage
-  then declares an explicit dependency on the lint stage via
-  `COPY --from=lint /src/go.sum /dev/null`, which forces BuildKit to complete
-  linting before proceeding to compilation and tests. This ensures lint failures
-  surface in seconds rather than minutes, without blocking on dependency
-  download or compilation in the build stage.
+- **Linting and testing run in Docker, as phases of the `Dockerfile`.** There is
+  no separate lint file. `script/lint` and `script/test` each build one phase
+  and nothing else:
 
-    The standard pattern for a Go repo Dockerfile is:
+    ```sh
+    docker build --no-cache --target lint -t "$(script/projectname)-lint" .
+    docker build --no-cache --target test -t "$(script/projectname)-test" .
+    ```
+
+    **A stage that is not the last one in the file is built only when the final
+    stage's chain depends on it, or when `--target` names it.** That is why the
+    two gates are always invoked by name here, and why the final stage carries a
+    `COPY --from=` of a harmless file from each of them: without that edge a
+    plain `docker build .` builds the last stage alone and exits 0 having linted
+    and tested nothing.
+
+    **Every `docker build` in `script/` is tagged**, here and in
+    `script/cibuild` and `script/docker`. An untagged build leaves a dangling
+    image behind on every invocation, on every developer host and every CI
+    runner; a tagged one replaces the previous image.
+
+    Inside a phase the tool is invoked directly — `golangci-lint`, `go test`,
+    `eslint`, `prettier` — never through `make lint` or `script/test`, which are
+    themselves a `docker build` and would recurse into a daemon that does not
+    exist in a build step. Formatting is the exception and stays on the host:
+    `script/fmt` writes the working tree, and `script/fmt-check` is its
+    read-only twin.
+
+    **No lint verdict may come from a host invocation of the linter.** On a
+    shared host golangci-lint reads a result cache keyed on file content rather
+    than location, so a second checkout of the same content is served the first
+    one's findings, and a host-global lock in `$TMPDIR` makes concurrent runs
+    exit non-zero with `parallel golangci-lint is running` — a status a caller
+    cannot tell from real findings. Both have produced wrong verdicts in this
+    org, in both directions. A container has its own cache, its own `TMPDIR` and
+    a digest-pinned binary, so neither is reachable.
+
+- **Any build that runs checks is built with `--no-cache`.** Docker invalidates
+  a `COPY` layer only when the copied content changes, so on an unchanged tree
+  the check `RUN` is served from cache, nothing executes, and the build still
+  exits 0. Every `docker build` in `script/` therefore passes `--no-cache`:
+  `script/lint`, `script/test`, `script/cibuild` and `script/docker` are the
+  four, and there is no fifth — `script/check` runs the two gate phases and
+  `script/fmt-check`, and builds no image of its own. A bare `docker build .` is
+  not evidence that anything ran: a sub-second build reporting success is a
+  cache hit, not a result. Never invalidate by pruning — `docker builder prune`
+  and friends destroy a build cache shared with every other build on the host.
+
+- **The gate phases are separate stages, and the build stage depends on both.**
+  The lint phase is based on the `golangci/golangci-lint` image (pinned by
+  hash), so lint failures surface in seconds rather than after a full compile,
+  and the test phase is based on the Go image. The canonical Go repo
+  `Dockerfile`:
 
     ```dockerfile
-    # Lint stage — fast feedback on formatting and lint issues
+    # Lint phase
     # golangci/golangci-lint:v2.x.x, YYYY-MM-DD
     FROM golangci/golangci-lint@sha256:... AS lint
     WORKDIR /src
     COPY go.mod go.sum ./
     RUN go mod download
     COPY . .
-    RUN make fmt-check
-    RUN make lint
+    RUN golangci-lint run --config .golangci.yml ./...
 
-    # Build stage
+    # Test phase
     # golang:1.x-alpine, YYYY-MM-DD
+    FROM golang@sha256:... AS test
+    WORKDIR /src
+    COPY go.mod go.sum ./
+    RUN go mod download
+    COPY . .
+    RUN go test -timeout 90s -race -cover ./... || \
+        { echo "--- Rerunning with -v for details ---"; \
+          go test -timeout 90s -race -v ./...; exit 1; }
+
+    # Build stage. Nothing is wanted from either phase above; the copies
+    # are what make BuildKit build them first, so this stage cannot run
+    # unless lint and test passed.
+    # golang:1.x-alpine, YYYY-MM-DD
     FROM golang@sha256:... AS builder
+    COPY --from=lint /src/go.sum /dev/null
+    COPY --from=test /src/go.sum /dev/null
     WORKDIR /src
-
-    # Force BuildKit to run the lint stage before proceeding
-    COPY --from=lint /src/go.sum /dev/null
-
     COPY go.mod go.sum ./
     RUN go mod download
     COPY . .
-    RUN make test
 
     ARG VERSION=dev
     RUN CGO_ENABLED=0 go build -trimpath \
         -ldflags="-s -w -X main.Version=${VERSION}" \
         -o /app ./cmd/app/
 
-    # Runtime stage
+    # Runtime stage, and the last one
     FROM alpine@sha256:...
     COPY --from=builder /app /usr/local/bin/app
     ENTRYPOINT ["app"]
     ```
 
     Key points:
-    - The lint stage uses the `golangci/golangci-lint` image directly (it
-      includes both Go and the linter), so there is no need to install the
-      linter separately.
-    - `COPY --from=lint /src/go.sum /dev/null` is a no-op file copy that creates
-      a stage dependency. BuildKit runs stages in parallel by default; without
-      this line, the build stage would not wait for lint to finish and a lint
-      failure might not fail the overall build.
+    - The lint phase uses the `golangci/golangci-lint` image directly (it has
+      both Go and the linter), so nothing needs installing.
+    - `COPY --from=<phase> /src/go.sum /dev/null` is a no-op copy whose only
+      purpose is the ordering edge. BuildKit runs stages in parallel by default,
+      and a stage nothing depends on is not built at all, so without these two
+      lines a red gate would not fail the build.
+    - Keep the runtime stage last, and if you add a stage after it, give it the
+      same two copies. A plain `docker build .` builds the last stage's chain
+      and nothing else.
     - If the project uses `//go:embed` directives that reference build artifacts
-      (e.g. a web frontend compiled in a separate stage), the lint stage must
+      (e.g. a web frontend compiled in a separate stage), the lint phase must
       create placeholder files so the embed directives resolve. Example:
       `RUN mkdir -p web/dist && touch web/dist/index.html web/dist/style.css`.
-      The lint stage should not depend on the actual build output — it exists to
-      fail fast.
     - If the project requires CGO or system libraries for linting (e.g.
-      `vips-dev`), install them in the lint stage with `apk add`.
-    - The build stage runs `make test` after compilation setup. Tests run in the
-      build stage, not the lint stage, because they may require compiled
-      artifacts or heavier dependencies.
+      `vips-dev`), install them in the lint phase with `apk add`.
+    - `ARG VERSION=dev` is declared in the stage that compiles and supplied by
+      `script/docker` and `script/cibuild`; no stage may call `git describe`.
 
 - Every repo should have a Gitea Actions workflow (`.gitea/workflows/`) that
-  runs `script/cibuild` (which runs `docker build .`) on push. Since the
-  Dockerfile already runs `make check`, a successful build implies all checks
-  pass.
+  runs `script/cibuild` on push, and checks out the repo as its only other step.
+  That script bootstraps, runs the gate phases, and then builds the image, so a
+  successful run means every check passed; a bare `docker build .` does not
+  carry the same guarantee, because its gate phases may come from the cache. The
+  image build is uncached and so runs the gate phases a second time. That is the
+  price of the rule above, and it is worth paying: the image that ships is built
+  from a run of its own gates rather than from a cache entry.
 
 - Use platform-standard formatters: `black` for Python, `prettier` for
   JS/CSS/Markdown/HTML, `go fmt` for Go. Always use default configuration with
@@ -189,14 +253,21 @@ style conventions are in separate documents:
   module under test to verify it compiles/parses. There is no excuse for
   `make test` to be a no-op.
 
-- `make test` must complete in under 20 seconds. Add a 30-second timeout in the
-  Makefile.
+- `make test` must complete in under 60 seconds. That is the hard cap, and a
+  suite that exceeds it fails. Under 20 seconds is the target. A suite between
+  20 and 60 seconds is still green, but the overage must be filed as an
+  improvement bug against that repo. Add a 90-second timeout to the test
+  invocation (`go test -timeout 90s`). The backstop deliberately sits above the
+  hard cap so that it catches a genuinely hung test rather than a merely slow
+  one.
 
-- **`make test` should use the conditional verbose rerun pattern.** Run tests
-  without `-v` (verbose) first. If tests fail, automatically rerun with `-v` to
-  show full output. This keeps CI logs and `docker build` output clean on
-  success (just package/suite summaries) while providing full diagnostic detail
-  on failure (every test case, every assertion). The general shell pattern:
+- **The test command should use the conditional verbose rerun pattern.** Run
+  tests without `-v` (verbose) first. If tests fail, automatically rerun with
+  `-v` to show full output. This keeps CI logs and `docker build` output clean
+  on success (just package/suite summaries) while providing full diagnostic
+  detail on failure (every test case, every assertion). The command lives in the
+  `test` phase of the `Dockerfile`, since `script/test` builds that phase; the
+  Makefile form below is the same pattern for any repo-local invocation:
 
     ```makefile
     test:
@@ -209,11 +280,24 @@ style conventions are in separate documents:
 
     ```makefile
     test:
-    	@go test -timeout 30s -race -cover ./... || \
+    	@go test -count=1 -timeout 90s -race -cover ./... || \
     		{ echo "--- Rerunning with -v for details ---"; \
-    		  go test -timeout 30s -race -v ./...; exit 1; }
+    		  go test -count=1 -timeout 90s -race -v ./...; exit 1; }
     ```
 
+    `-count=1` is required on both invocations: it defeats Go's test _result_
+    cache, so the target cannot report a pass it did not earn, and the rerun
+    reproduces a failure instead of replaying it. It leaves the build cache
+    alone, so it costs the runtime of the suite and no recompilation.
+
+    Note that this is a second, independent cache, stacked below the Docker
+    layer cache that [issue #26](https://git.eeqj.de/sneak/prompts/issues/26)
+    addresses. `CHECK_EPOCH` guarantees the `RUN make test` _step_ re-executes;
+    it does not guarantee `go test` inside that step does any work, because the
+    `GOCACHE` baked into earlier image layers survives into the re-executed
+    step. They are two separate defects requiring two separate fixes, and a fix
+    for one must not be recorded as covering the other.
+
     Python example:
 
     ```makefile
@@ -239,10 +323,83 @@ style conventions are in separate documents:
   must be in `.gitignore`. No exceptions.
 
 - `.gitignore` should be comprehensive from the start: OS files (`.DS_Store`),
-  editor files (`.swp`, `*~`), language build artifacts, and `node_modules/`.
-  Fetch the standard `.gitignore` from
-  `https://git.eeqj.de/sneak/prompts/raw/branch/main/.gitignore` when setting up
-  a new repo.
+  editor files (`.swp`, `*~`), in-repo agent scratch directories (`.claude/`),
+  language build artifacts, and `node_modules/`. Fetch the standard `.gitignore`
+  from `https://git.eeqj.de/sneak/prompts/raw/branch/main/.gitignore` when
+  setting up a new repo. These patterns are written to `.gitignore`'s own
+  semantics, in which an unanchored pattern already matches at every depth; they
+  are not a `.dockerignore` and must not be transplanted into one unmodified.
+
+- **`.dockerignore` does not use `.gitignore` semantics, and copying patterns
+  across unmodified leaves secrets in the build context.** Docker matches with
+  `moby/patternmatcher`: `filepath.Match` semantics plus a `**` extension, so
+  `*` does not cross `/` and a pattern without a leading `**/` is anchored at
+  the build-context root. A `.dockerignore` listing `.env`, `*.pem` and `*.key`
+  therefore excludes only the copies at the repository root, while `config/.env`
+  and `certs/server.key` still reach the context and can land in an image layer
+  — which is more dangerous than a short file with no secret patterns at all,
+  because it reads as solved and stops anyone looking. Give every
+  depth-independent pattern the `**/` prefix and leave only genuinely
+  root-anchored entries unprefixed: `.git`, and the repo's own host-built
+  binary, written `/myapp` and never `**/myapp`, which would also match
+  `cmd/myapp/` and delete the package directory from the context. Matching is
+  case-sensitive, and an ALL-CAPS twin per pattern still misses `Server.Key`, so
+  secret names use character ranges — `**/*.[kK][eE][yY]`, `**/*.[pP][eE][mM]`,
+  and likewise for `.envrc` and the extensionless SSH keys. Where such a pattern
+  also catches something the build needs, re-include it with a negation
+  (`!docs/example.env`); deleting the pattern reopens the exposure for every
+  other file it covers. Fetch the standard `.dockerignore` from
+  `https://git.eeqj.de/sneak/prompts/raw/branch/main/.dockerignore` and extend
+  it with the repo's own artifacts.
+
+- **In-repo agent scratch belongs in both files, written to each file's own
+  semantics.** `.claude/` holds one worktree per in-flight agent — an entire
+  additional checkout of the repo — so under `COPY . .` the build context
+  inflates by a multiple of the repo and another session's unreviewed work can
+  be copied into an image layer. In `.gitignore` the entry is `.claude/`,
+  unanchored. In `.dockerignore` it is `.claude`, anchored and with **no** `**/`
+  prefix, because the prefixed form would also delete any nested directory of
+  that name from the build. Anchoring carries a known gap that the canonical
+  `.dockerignore` states in its own comment, since consuming repos receive the
+  file and not the tracker: the directory is created in the agent's working
+  directory, so a repo running agents in subdirectories still ships
+  `services/api/.claude/` and must add its own anchored entry there.
+
+- **Excluding `.git` means `git describe` cannot run inside any build stage, and
+  it fails quietly there.** In a build stage there is no repository, so
+  `git describe` writes nothing to stdout, `-X main.Version=` comes out empty,
+  the binary reports no version at all, and the build still exits 0. Compute the
+  version on the host and thread it in as a build arg. `script/docker` and
+  `script/cibuild` do this, byte-identically across repos:
+
+    ```sh
+    # Own line: a failing command substitution inside an argument does not
+    # trip `set -e`, so the inline form degrades to an empty constant.
+    version="$(git describe --tags --always --dirty 2>/dev/null || true)"
+    [ -n "$version" ] || version="unknown"
+    docker build --no-cache \
+        --build-arg VERSION="$version" \
+        -t "$(script/projectname)" .
+    ```
+
+    `--always` makes an untagged repo yield an abbreviated commit hash rather
+    than failing, and the `[ -n "$version" ]` line is the single place the
+    fallback is applied — a live check that fires on a build from an export with
+    no `.git` and on a repository with no commits yet. Do not fold it into the
+    substitution as `|| echo unknown`, which makes the guard unreachable. The
+    Dockerfile's side is `ARG VERSION=dev` in the stage that compiles, declared
+    there because `ARG` is stage-scoped; passing `VERSION` to a repo whose
+    Dockerfile declares no such `ARG` is ignored and costs nothing, which is why
+    the scripts stay byte-identical. One consequence for CI: the standard
+    checkout action clones shallow and fetches no tags, so a repo that embeds a
+    tag-derived version must set `fetch-depth: 0` on its checkout step.
+
+- **Verify `.dockerignore` by enumerating the image, not by reading the
+  patterns.** Plant files at the root _and_ at least two directories deep, build
+  a probe image that does `COPY . .`, and list what actually landed
+  (`docker run --rm --entrypoint find IMAGE /app`). The `transferring context`
+  size is not a substitute: a nested secret is a few bytes, and BuildKit
+  transfers only the delta from the previous build.
 
 - **No build artifacts in version control.** Code-derived data (compiled
   bundles, minified output, generated assets) must never be committed to the
@@ -258,9 +415,45 @@ style conventions are in separate documents:
 - Make all changes on a feature branch. You can do whatever you want on a
   feature branch.
 
-- `.golangci.yml` is standardized and must _NEVER_ be modified by an agent, only
-  manually by the user. Fetch from
-  `https://git.eeqj.de/sneak/prompts/raw/branch/main/.golangci.yml`.
+- `.golangci.yml` is standardized. The vendored copy in a consuming repo must
+  _NEVER_ be modified by an agent: fetch it from
+  `https://git.eeqj.de/sneak/prompts/raw/branch/main/.golangci.yml` and keep it
+  byte-identical, so that no repo can quietly loosen its own linting. Linter
+  configuration changes are made to the canonical copy in the `prompts` repo and
+  reach consuming repos by re-vendoring; an agent may open a PR against
+  canonical, which only the user merges. One list is exempt from byte-identity,
+  because it cannot be written once for every repo: the `deny` list of the
+  `test-support` depguard rule, where a repo names its own test-support packages
+  by full import path. A repo adds entries there and changes nothing else, and a
+  re-vendor carries its entries forward. The canonical golangci-lint version is
+  v2.12.2 (released 2026-05-06), pinned as the digest of the lint phase's base
+  image
+  (`golangci/golangci-lint@sha256:5cceeef04e53efe1470638d4b4b4f5ceefd574955ab3941b2d9a68a8c9ad5240`,
+  which reports `2.12.2 built with go1.26.2 from c0d3ddc9`). That digest is the
+  only pin, since no repo installs golangci-lint on the host: bumping the
+  version means changing it and nothing else.
+
+- **`script/bootstrap` installs a pinned tool by comparing versions, never by
+  testing presence.** An `if ! command -v <tool>; then install; fi` guard tests
+  `PATH` only, so on an already-provisioned machine the pin is inert and a
+  version bump is a silent no-op — while the Dockerfile, installing into a clean
+  image, gets the pinned version, so a local `make check` and `make docker` can
+  disagree about what the tool even is. The canonical form:
+    - compares the installed version against the pin over the **whole** version
+      token; a parser that stops at the first `-` reports `2.12.2` for a host
+      running `2.12.2-rc1` and skips the install;
+    - treats absent, non-zero, empty or unrecognised `--version` output as a
+      mismatch, so the failure direction is a redundant install and never a
+      skipped one;
+    - after installing, re-resolves the binary the way callers do — `hash -r`,
+      then through `PATH`, not through the directory the installer wrote to —
+      and fails naming the resolved path, since an install that a shadowing
+      binary hides succeeds while changing nothing any caller sees;
+    - is actually called, and prints the version on both success paths: a
+      function defined and never invoked has the same exit status and the same
+      empty output as one that worked.
+
+    Keep it POSIX sh: no arrays, no `[[`, no `grep -P`.
 
 - When pinning images or packages by hash, add a comment above the reference
   with the version and date (YYYY-MM-DD).
@@ -379,7 +572,9 @@ style conventions are in separate documents:
   language-specific config). Everything else goes in a subdirectory. Canonical
   subdirectory names:
     - `bin/` — executable scripts and tools
-    - `cmd/` — Go command entrypoints
+    - `cmd/` — Go command entrypoints; thin only: one `main.go` per binary whose
+      body is a single call into `internal/` or `pkg/`, no project logic in
+      `cmd/`
     - `configs/` — configuration templates and examples
     - `deploy/` — deployment manifests (k8s, compose, terraform)
     - `docs/` — documentation and markdown (README.md stays in root)

TODO.md

@@ -1,28 +1,27 @@
 # Workflow
 
-* branch per issue from `next`
-* do the work in Next Step
-* move Next Step to the top of Completed Steps
-* `TODO.md` merges with git's union merge (`.gitattributes`), which never
+- branch per issue from `next`
+- do the work in Next Step
+- move Next Step to the top of Completed Steps
+- `TODO.md` merges with git's union merge (`.gitattributes`), which never
   reports a conflict: read the merged entries after every merge or rebase
-* move the top item of Future Steps into Next Step
-* commit (`TODO.md` changes in the same commit as the work)
-* open a PR based on `next`
-* an independent reviewer who did not write the change gates it
-* the manager squash-merges the PR into `next` once review passes
-* `next` stays green and mergeable to `main` at any time; only the owner
-  merges `next` into `main`, via the single milestone PR
-* push
+- move the top item of Future Steps into Next Step
+- commit (`TODO.md` changes in the same commit as the work)
+- open a PR based on `next`
+- an independent reviewer who did not write the change gates it
+- the manager squash-merges the PR into `next` once review passes
+- `next` stays green and mergeable to `main` at any time; only the owner merges
+  `next` into `main`, via the single milestone PR
+- push
 
 # Status
 
-pre-1.0. No git tags exist. The `1.0.0` milestone is in progress; work
-lands on `next`, and `main` receives only the milestone PR that the
-owner merges. `next` is at the canonical `golangci-lint` v2.12.2 config
-and is green. Recent work extracted the internal/magic,
-internal/allowlist, internal/httpfetcher, and internal/signature
-packages. The gosec findings from the 2026-07-06 survey are resolved.
-The disk cache is now size-bounded with LRU eviction
+pre-1.0. No git tags exist. The `1.0.0` milestone is in progress; work lands on
+`next`, and `main` receives only the milestone PR that the owner merges. `next`
+is at the canonical `golangci-lint` v2.12.2 config and is green. Recent work
+extracted the internal/magic, internal/allowlist, internal/httpfetcher, and
+internal/signature packages. The gosec findings from the 2026-07-06 survey are
+resolved. The disk cache is now size-bounded with LRU eviction
 (`cache_max_bytes`), closing the unbounded disk growth DoS vector.
 
 # Next Step
@@ -31,6 +30,126 @@ P2: security: per-IP rate limiting on the image routes
 
 # Completed Steps
 
+- 2026-10-05 the format `auto` (closes #88): a format in the `/v1/image/` path,
+  an encrypted URL's token and the generator page's format choice, chosen for
+  each request from `Accept` once the signature or token is checked: AVIF when
+  the header names `image/avif`, else WebP when it names `image/webp`, else JPEG
+  when the first of `image/jpeg`, `image/*` and `*/*` that it names allows it,
+  or when it names nothing; `q=0` refuses a format. AVIF and WebP must be named,
+  as clients that cannot show them send the wildcards too. A header that allows
+  none of the three answers 406, one that does not parse 400. The signature and
+  the token cover `auto` itself; the cache key and `ETag` use the format chosen.
+  Answers from the point the format is chosen carry `Vary: Accept`, next to the
+  CORS `Vary: Origin`; fixed-format answers do not.
+- 2026-10-05 the markdown is formatted with prettier (closes #100): `script/fmt`
+  and `script/fmt-check` run prettier 3.8.1, pinned in `package.json` and
+  `yarn.lock`, on `**/*.md` after `gofmt`, with four-space tabs and
+  `proseWrap: always` as `.prettierrc` says; `.prettierignore` keeps it off
+  `REPO_POLICIES.md`, the copy from `sneak/prompts`, and `vendor/`. Plain
+  `script/bootstrap` installs Node and Yarn as the one in `sneak/prompts` does
+  and then prettier; `script/bootstrap --cgo` does not, as the `Dockerfile`
+  stages that run it format nothing. The HTML templates stay unformatted:
+  prettier cannot parse a Go template action inside a tag. The markdown was
+  reflowed in a commit of its own.
+- 2026-10-05 lint and tests run as the `lint` and `test` phases of the
+  `Dockerfile`, built with `--no-cache` (closes #202): `script/check`,
+  `script/cibuild`, `script/docker`, `script/lint`, `script/test`,
+  `script/setup` and `script/install-precommit` are now the copies from
+  `sneak/prompts` `main`, unchanged. The `lint` phase runs golangci-lint from
+  the image `REPO_POLICIES.md` names, with `libvips-dev` from `apt-get`; the
+  `test` phase runs the tests with a 90-second timeout; the build stage depends
+  on both. `Dockerfile.lint` and the `CHECK_EPOCH` build argument are gone, the
+  formatting check runs on the host, and `make docker-versioned` and
+  `make docker-test` call the scripts. `script/bootstrap`, `script/fmt`,
+  `script/fmt-check`, `script/precommit` and `script/projectname` stay pixa's
+  own. `script/bootstrap` installs git, make and Go, refreshing apt's package
+  lists before its first apt install; with `--cgo`, which only the `test` phase
+  and the build stage pass, it also installs the C compiler and the libvips and
+  libheif libraries. The stage that compiles still takes the version from
+  `git describe` when no `VERSION` is given, per
+  https://git.eeqj.de/sneak/pixa/issues/166, so the copied scripts' comment that
+  `.dockerignore` leaves out `.git` does not hold for pixa.
+- 2026-10-04 load test (closes #81): `script/loadtest [duration [clients]]`
+  (`make loadtest`, defaults `10s` and `4`), a benchmark that `script/check`
+  does not run, measures three scenarios, each against a new pixad container and
+  a new upstream host, `cmd/loadtest-origin`: `hit` (one cached image), `miss`
+  (a new source image every request) and `herd` (each new source image asked for
+  by all clients at once). For each it prints vegeta's report (requests per
+  second, latency percentiles, status codes), pixad's peak resident memory and
+  the requests that reached the origin. `README.md` says how to run it and read
+  it, and keeps 1-5k r/s as a target not yet measured. First measurement, with
+  the defaults on a shared 48-CPU machine with other work running: a baseline
+  for later changes, not a test of the target. `hit` 1413 r/s, p50 0.7 ms, p95
+  8.7 ms, p99 44 ms, peak 53 MiB (4 clients that each wait for their answer, so
+  not pixad's limit); `miss` 70 r/s, p50 52 ms, p95 91 ms, p99 122 ms, peak 100
+  MiB, one fetch per request; `herd` 74 r/s, p50 52 ms, p95 69 ms, p99 111 ms,
+  peak 60 MiB, 188 fetches for 749 requests.
+- 2026-10-04 the CI checkout fetches the tags (closes #208): the checkout step
+  in `.gitea/workflows/check.yml` sets `fetch-depth: 0`, as `REPO_POLICIES.md`
+  asks of a repo that takes its version from the tags, so a CI build of a tagged
+  commit stamps the tag from `git describe` instead of a bare commit.
+- 2026-10-04 `config.yml` stays out of git and the Docker build context (closes
+  #212): `.gitignore` now ignores `config.yml`, the config file Getting Started
+  creates with the signing key, and `.dockerignore` leaves it out in every
+  directory and in any letter case, as it already did `config.yaml` and
+  `config.dev.yml`.
+- 2026-10-04 local config files stay out of the Docker build context (closes
+  #211): `.dockerignore` now leaves out `config.yaml` and `config.dev.yml` in
+  every directory and in any letter case, the local config files `.gitignore`
+  keeps out of git because they can hold the signing key.
+  `configs/config.example.yml` is still sent. `config.yml`, which Getting
+  Started creates, is in neither file:
+  https://git.eeqj.de/sneak/pixa/issues/212.
+- 2026-10-04 `cmd/pixad/main.go` is one call into `internal/` (closes #206):
+  what it did (the command line and its `--config` flag, setting
+  `PIXA_CONFIG_PATH`, ignoring `SIGPIPE`, starting the fx app) is now `Run` in
+  `internal/app`, unchanged, and `main` calls it with `Version`, which the build
+  still sets through `-X main.Version`. That code had no tests to move.
+- 2026-10-04 `.gitignore` ignores `.claude/` (closes #204): the entry and its
+  comment are copied from the canonical `.gitignore` in `sneak/prompts`,
+  unanchored so it matches at every depth. `.dockerignore` already has
+  `.claude`.
+- 2026-10-04 `.dockerignore` keeps secrets out at every depth (closes #205): the
+  file is now the standard one from `sneak/prompts`, whose patterns match in
+  every directory and, for environment files and private keys, in any letter
+  case, so a nested `.env` or `server.key` no longer reaches the build context.
+  pixa still sends `.git` without `.git/config` in place of the standard file's
+  `.git` line, and still leaves out `.gitignore`, `/bin` and `/data`.
+- 2026-10-04 `REPO_POLICIES.md` matches the canonical copy again (closes #196):
+  it is replaced, unchanged, by `prompts/REPO_POLICIES.md` from `sneak/prompts`
+  `main`. The rules it adds that pixa's tree breaks are filed:
+  https://git.eeqj.de/sneak/pixa/issues/202 (lint and tests as `Dockerfile`
+  phases built with `--no-cache`), https://git.eeqj.de/sneak/pixa/issues/203
+  (the workflow's `script/docker-smoke` step),
+  https://git.eeqj.de/sneak/pixa/issues/204 (`.claude/` in `.gitignore`),
+  https://git.eeqj.de/sneak/pixa/issues/205 (`.dockerignore` patterns at every
+  depth), https://git.eeqj.de/sneak/pixa/issues/206 (a thin `cmd/pixad/main.go`)
+  and https://git.eeqj.de/sneak/pixa/issues/208 (`fetch-depth: 0` on the CI
+  checkout, so the build sees the tags). Its rule that no build stage runs
+  `git describe` is not followed: pixa takes the version from the `.git` in the
+  build context, per https://git.eeqj.de/sneak/pixa/issues/166, as the copy on
+  `sneak/prompts` `next` already says.
+- 2026-10-04 an integration test of the image proxy flow (closes #80):
+  `TestImageProxyFlow` in `internal/server` starts the database, handlers and
+  middleware from the constructors `pixad` uses, with a fresh state directory,
+  and replaces only the upstream origin with a local test server. For a resize
+  with a change to JPEG and for `orig`, the first request goes through the
+  router, the real fetcher, libvips, the disk cache and SQLite and answers 200
+  with the right content type and size and `X-Pixa-Cache: MISS`; the second
+  answers `HIT` with the same image and the upstream has had one request; the
+  source and the converted image are then in `cache/sources` and
+  `cache/variants`, with their rows in `source_content`, `source_metadata` and
+  `variant_content`. Two optional fields make this possible, which `pixad` does
+  not set and the config file and environment cannot:
+  `httpfetcher.Config.DialContext` connects in place of the dialer that refuses
+  internal addresses, the URL and redirect checks still running, and
+  `handlers.Params.Fetcher` replaces the fetcher the handlers build.
+- 2026-10-04 a URL made on the generator page with a `ttl` is tested to expire
+  (closes #199): a new test in `internal/handlers` makes a URL on the generator
+  page with a `ttl` of one second, checks that `/v1/e/` serves it at once, waits
+  two seconds and checks that it then answers 410. The test waits for real, as
+  pixa reads the clock directly when it makes and checks a URL; it waits two
+  seconds because the time a URL expires is kept in whole seconds. Test only.
 - 2026-10-04 referer blocklist (closes #90): `referer_blocklist`
   (`PIXA_REFERER_BLOCKLIST`) lists hosts, written and matched as for
   `allowlist_hosts` with the same matcher; an entry of either list that is
@@ -48,30 +167,29 @@ P2: security: per-IP rate limiting on the image routes
   `README.md`, the comments in `internal/config/config.go` and the startup error
   for the placeholder signing key name the new path; `scripts/manual-test.sh`
   and its directory are deleted, as the handler tests in `internal/handlers`
-  cover every check it made except two: fetching a real image from the
-  internet, and a URL made on the generator page with a `ttl` answering 410 once
-  the `ttl` has passed (https://git.eeqj.de/sneak/pixa/issues/199);
-  `CONVENTIONS.md` is deleted, as `REPO_POLICIES.md` links the canonical Go HTTP
-  server conventions.
+  cover every check it made except two: fetching a real image from the internet,
+  and a URL made on the generator page with a `ttl` answering 410 once the `ttl`
+  has passed (https://git.eeqj.de/sneak/pixa/issues/199); `CONVENTIONS.md` is
+  deleted, as `REPO_POLICIES.md` links the canonical Go HTTP server conventions.
 - 2026-10-04 SQLite writes no longer fail with "database is locked" (closes
   #198): pixa adds `_pragma=busy_timeout(5000)` to every `db_url`, so a write
   that finds another in progress on another connection waits up to five seconds
   for it, and the default `db_url` turns on WAL mode with
   `_pragma=journal_mode(WAL)`. The old default's `_journal_mode=WAL` is not a
   parameter the driver reads, so the database was never in WAL mode.
-- 2026-10-04 `TestPeriodicReconciliationAdoptsFileThatAppearsAfterStartup`
-  only passes through a periodic pass (closes #189): it slept for three
-  eviction intervals before writing its file, and a startup pass still running
-  then could adopt the file itself. It now holds the test database's only
-  connection until the startup pass waits for it after walking the empty
-  variant directory, writes the file and lets the connection go, as
+- 2026-10-04 `TestPeriodicReconciliationAdoptsFileThatAppearsAfterStartup` only
+  passes through a periodic pass (closes #189): it slept for three eviction
+  intervals before writing its file, and a startup pass still running then could
+  adopt the file itself. It now holds the test database's only connection until
+  the startup pass waits for it after walking the empty variant directory,
+  writes the file and lets the connection go, as
   `TestEvictionRunsOnPeriodicSchedule` does, so only a periodic reconciliation
   pass can adopt the file. Test only.
 - 2026-10-04 logging in, logging out, the URL generator and `/v1/e/` have
-  handler tests (closes #77): new tests in `internal/handlers`, with no
-  network, check that `GET /` without a login session shows the login form; a
-  wrong key shows it again with an error and sets no session cookie; the right
-  key answers 303 to `/` with a session cookie marked `Secure`, `HttpOnly` and
+  handler tests (closes #77): new tests in `internal/handlers`, with no network,
+  check that `GET /` without a login session shows the login form; a wrong key
+  shows it again with an error and sets no session cookie; the right key answers
+  303 to `/` with a session cookie marked `Secure`, `HttpOnly` and
   `SameSite=Strict`, with which `GET /` shows the generator page; `GET /logout`
   answers 303 to `/` with an empty session cookie sent with `Max-Age=0`;
   `POST /generate` without a login session answers 303 to `/`; `/v1/e/` serves
@@ -81,11 +199,11 @@ P2: security: per-IP rate limiting on the image routes
 - 2026-10-04 `TODO.md` merges with git's union merge (closes #190): a root
   `.gitattributes`, copied from `sneak/prompts`, marks it `merge=union`, so two
   branches that each add an entry at the top of Completed Steps merge without a
-  conflict and keep both entries. Git now never reports a conflict in
-  `TODO.md`: a real one keeps both versions of the lines, and two entries that
-  share an identical line can end up one inside the other, which a rebase can
-  do to an entry already on `next`. The Workflow above says to read the merged
-  entries after every merge or rebase.
+  conflict and keep both entries. Git now never reports a conflict in `TODO.md`:
+  a real one keeps both versions of the lines, and two entries that share an
+  identical line can end up one inside the other, which a rebase can do to an
+  entry already on `next`. The Workflow above says to read the merged entries
+  after every merge or rebase.
 - 2026-10-04 the default `cache_max_bytes` no longer shrinks as the cache fills
   (closes #184): for an omitted key, the cache works out the limit when it
   opens, after the database is open, as 75% of the sum of the free space on the
@@ -109,10 +227,10 @@ P2: security: per-IP rate limiting on the image routes
   that pixa may not enter, aborts startup naming the file, as a file that does
   not parse already did.
 - 2026-10-04 `.golangci.yml` re-vendored from the canonical copy (closes #57):
-  the deprecated `gomodguard` is switched off, so lint runs print no
-  deprecation warning; its successor `gomodguard_v2` runs with the shared
-  module block list, and `depguard` keeps `net/http/httptest` out of files that
-  are not tests. The tree needed no code changes.
+  the deprecated `gomodguard` is switched off, so lint runs print no deprecation
+  warning; its successor `gomodguard_v2` runs with the shared module block list,
+  and `depguard` keeps `net/http/httptest` out of files that are not tests. The
+  tree needed no code changes.
 - 2026-10-04 the Content-Security-Policy allows no inline script or style
   (closes #125): `script-src` and `style-src` are `'self'` only. The generator
   page's two inline `onclick` handlers moved into
@@ -131,30 +249,30 @@ P2: security: per-IP rate limiting on the image routes
   counts, the health check for a load balancer, what a stop does and its exit
   codes, and what running outside Docker needs; `configs/Caddyfile` is the
   example, checked with `caddy validate`.
-- 2026-10-04 the metrics basic auth, CORS preflight, request logging and
-  metrics recording have tests (closes #79): `MetricsAuth` on its own answers
-  401 with a challenge without credentials or with a wrong username or password
-  and lets the configured ones through; a preflight request gets `*` for any
-  origin when `access_control_allow_origin` is `*` and no
-  `Access-Control-Allow-Origin` from another origin than the configured one; a
-  `POST /` carrying the signing key leaves no trace of it in the request log
-  line, and the login handler's own log lines leave out the submitted key; the
-  metrics middleware on its own records a request it served, and the router
-  records nothing while no metrics username is set. Not tested: that the router
-  puts the basic auth in front of `/metrics` and records requests when a
-  metrics username is set. Only one test per package can set up `/metrics`, and
-  in `internal/server` that is `TestMaintenanceModeKeepsOtherRoutes`, which
-  needs the owner's approval to change; #180 holds it. Tests only; the basic
-  auth library already compares the password in constant time.
+- 2026-10-04 the metrics basic auth, CORS preflight, request logging and metrics
+  recording have tests (closes #79): `MetricsAuth` on its own answers 401 with a
+  challenge without credentials or with a wrong username or password and lets
+  the configured ones through; a preflight request gets `*` for any origin when
+  `access_control_allow_origin` is `*` and no `Access-Control-Allow-Origin` from
+  another origin than the configured one; a `POST /` carrying the signing key
+  leaves no trace of it in the request log line, and the login handler's own log
+  lines leave out the submitted key; the metrics middleware on its own records a
+  request it served, and the router records nothing while no metrics username is
+  set. Not tested: that the router puts the basic auth in front of `/metrics`
+  and records requests when a metrics username is set. Only one test per package
+  can set up `/metrics`, and in `internal/server` that is
+  `TestMaintenanceModeKeepsOtherRoutes`, which needs the owner's approval to
+  change; #180 holds it. Tests only; the basic auth library already compares the
+  password in constant time.
 - 2026-10-04 the image route's signature check and error answers are tested
   (closes #76): new tests in `internal/handlers`, with no network, check the
   status and JSON error body for a missing, wrong, unpadded, upper-case or
-  expired signature on a host not on the allowlist, or a valid one sent for
-  its parent domain, a sibling host, a subdomain or the host with another
-  domain appended (401), an unparseable path (400), `localhost` as the
-  upstream host (403) and an upstream error (502); that an allowlisted host is
-  served without a signature, another host only with a valid one; and the
-  answers of `/robots.txt` and the health check. No code changes.
+  expired signature on a host not on the allowlist, or a valid one sent for its
+  parent domain, a sibling host, a subdomain or the host with another domain
+  appended (401), an unparseable path (400), `localhost` as the upstream host
+  (403) and an upstream error (502); that an allowlisted host is served without
+  a signature, another host only with a valid one; and the answers of
+  `/robots.txt` and the health check. No code changes.
 - 2026-10-04 request IDs returned and passed on, and `/v1/e/` revalidates
   (closes #84): pixa's own `RequestID` middleware, in place of chi's, gives each
   request an ID, its own `X-Request-ID` when that is at most 64 letters, digits,
@@ -171,26 +289,26 @@ P2: security: per-IP rate limiting on the image routes
   `Vary: Accept` is left to #88.
 - 2026-10-04 routes, encrypted URLs and config file documented (closes #75):
   "Routes" in `README.md` lists every route with its method, purpose, what it
-  needs and the status codes it answers with, and says `q` and `fit` are part
-  of what is cached; "Encrypted URLs" covers logging in, making one on the
+  needs and the status codes it answers with, and says `q` and `fit` are part of
+  what is cached; "Encrypted URLs" covers logging in, making one on the
   generator page, how long it lasts and the 410 once it has expired;
   "Configuration" gives the order in which pixa looks for its config file;
   `config.example.yml` lists `db_url` and `env` and gives every key's default;
   `scripts/manual-test.sh` is left to #97.
 - 2026-10-04 shutdown stops cache eviction in progress (closes #102):
   `StartEviction` runs the eviction goroutine with its own context, which
-  `StopEviction` cancels, so a pass in progress stops at its next database
-  call, file, row or eviction candidate instead of running to completion, and
-  no pass starts after it, so a stop logs at most one warning;
-  `StopEviction` takes a context and, when that context ends before the
-  goroutine exits, stops waiting and returns its error; the handlers' stop hook
-  passes fx's stop context, so an eviction still running when fx's stop
-  deadline ends fails the stop and makes the exit code 1.
+  `StopEviction` cancels, so a pass in progress stops at its next database call,
+  file, row or eviction candidate instead of running to completion, and no pass
+  starts after it, so a stop logs at most one warning; `StopEviction` takes a
+  context and, when that context ends before the goroutine exits, stops waiting
+  and returns its error; the handlers' stop hook passes fx's stop context, so an
+  eviction still running when fx's stop deadline ends fails the stop and makes
+  the exit code 1.
 - 2026-10-04 dead code in `internal/imgcache` is gone (closes #73): `Purge`,
   which only returned an error and which nothing called, is no longer part of
-  the `ImageCache` interface or `Service`; the `SignatureValidator`,
-  `Allowlist` and `Storage` interfaces, which nothing implemented or used, are
-  deleted. Nothing else changes.
+  the `ImageCache` interface or `Service`; the `SignatureValidator`, `Allowlist`
+  and `Storage` interfaces, which nothing implemented or used, are deleted.
+  Nothing else changes.
 - 2026-10-04 upstream host semaphores and variant `.meta` files no longer
   outlive their use (closes #87): the fetcher counts the fetches holding or
   waiting for a slot of each upstream host's semaphore and removes the host's
@@ -202,21 +320,20 @@ P2: security: per-IP rate limiting on the image routes
   cache directories pixa uses (`cache/sources`, `cache/metadata`,
   `cache/variants`) and how files are named in each, and the comments in
   `001_schema.sql` name the same paths; the routes and the signature section
-  list the same output formats, `jpg` and `original` included; the TLS
-  sentence names `allow_http` as its exception; "Metrics" says only generic
-  HTTP and Go runtime metrics exist, measured and served only when the metrics
-  username and password are set.
-- 2026-10-03 shutdown sets the exit code and waits for image processing
-  (closes #86): fx alone handles SIGINT and SIGTERM, and the server's own
-  signal handler is gone; fx's `Run` in `cmd/pixad` exits with the shutdown's
-  code: 0 for a signal, 1 when the HTTP server cannot listen or the app fails
-  to start or to stop; the server's stop hook, which fx waits for, stops the
-  HTTP server, waits for the images still being processed, both within 5
-  seconds, then flushes Sentry; images still being processed after that are
-  logged with their count and make the exit code 1; a Sentry DSN that cannot be
-  used fails startup, so the stop hooks of what had already started run,
-  instead of exiting the process from a goroutine; the eviction loop is left to
-  #102.
+  list the same output formats, `jpg` and `original` included; the TLS sentence
+  names `allow_http` as its exception; "Metrics" says only generic HTTP and Go
+  runtime metrics exist, measured and served only when the metrics username and
+  password are set.
+- 2026-10-03 shutdown sets the exit code and waits for image processing (closes
+  #86): fx alone handles SIGINT and SIGTERM, and the server's own signal handler
+  is gone; fx's `Run` in `cmd/pixad` exits with the shutdown's code: 0 for a
+  signal, 1 when the HTTP server cannot listen or the app fails to start or to
+  stop; the server's stop hook, which fx waits for, stops the HTTP server, waits
+  for the images still being processed, both within 5 seconds, then flushes
+  Sentry; images still being processed after that are logged with their count
+  and make the exit code 1; a Sentry DSN that cannot be used fails startup, so
+  the stop hooks of what had already started run, instead of exiting the process
+  from a goroutine; the eviction loop is left to #102.
 - 2026-10-03 every `script/cibuild` and `script/docker` run executes the checks
   (closes #101): the `Dockerfile` declares `CHECK_EPOCH` above `make fmt-check`
   and `make lint` in the lint stage and above `make test` in the build stage,
@@ -231,11 +348,11 @@ P2: security: per-IP rate limiting on the image routes
   upstream fetch or cached source read and one transcode through
   `golang.org/x/sync/singleflight`; the first request's processing ignores its
   cancellation but keeps its deadline, and the others wait for its image or
-  error holding no upstream connection or processing slot, and stop waiting
-  when their own context ends; the request doing the processing waits for it
-  even then, up to its deadline; a request whose context has already ended
-  starts nothing; each request counts one miss, and the processing counts its
-  fetch and transcode once; a panic while processing is reported to Sentry when
+  error holding no upstream connection or processing slot, and stop waiting when
+  their own context ends; the request doing the processing waits for it even
+  then, up to its deadline; a request whose context has already ended starts
+  nothing; each request counts one miss, and the processing counts its fetch and
+  transcode once; a panic while processing is reported to Sentry when
   `sentry_dsn` is set and becomes an error for every waiting request instead of
   stopping pixad; documented in `README.md`.
 - 2026-09-29 only the image routes send CORS headers (closes #98): the CORS
@@ -244,20 +361,20 @@ P2: security: per-IP rate limiting on the image routes
   still answers a preflight `OPTIONS` request; the login and URL generator
   pages, `/metrics` and the other routes send no `Access-Control-Allow-Origin`;
   documented in `README.md` and `config.example.yml`.
-- 2026-10-02 a plain `docker build .` stamps the tag or short commit, not
-  `dev` (closes #166): `.dockerignore` lets `.git` into the build context,
-  without `.git/config`; with no `VERSION` build argument the `Dockerfile`
-  takes the version from `git describe --tags --always`, and fails the build if
-  the context carries `.git` and no version comes out; `ARG VERSION` has no
-  default; pixad logs its version, with its name and architecture, as its first
-  log line at startup.
-- 2026-09-29 the container makes `/var/lib/pixa` usable by itself (closes
-  #159): `deploy/docker-entrypoint.sh` creates the directory if it is missing,
-  gives the directory and everything in it to `pixad` when the directory or one
-  of its top-level entries belongs to another user or group, sets its mode to
-  `750`, then runs the server as `pixad`; data left by an earlier run under
-  another uid is taken over this way; "Running under upaas" in `README.md` no
-  longer tells the operator to create or chown the host directory.
+- 2026-10-02 a plain `docker build .` stamps the tag or short commit, not `dev`
+  (closes #166): `.dockerignore` lets `.git` into the build context, without
+  `.git/config`; with no `VERSION` build argument the `Dockerfile` takes the
+  version from `git describe --tags --always`, and fails the build if the
+  context carries `.git` and no version comes out; `ARG VERSION` has no default;
+  pixad logs its version, with its name and architecture, as its first log line
+  at startup.
+- 2026-09-29 the container makes `/var/lib/pixa` usable by itself (closes #159):
+  `deploy/docker-entrypoint.sh` creates the directory if it is missing, gives
+  the directory and everything in it to `pixad` when the directory or one of its
+  top-level entries belongs to another user or group, sets its mode to `750`,
+  then runs the server as `pixad`; data left by an earlier run under another uid
+  is taken over this way; "Running under upaas" in `README.md` no longer tells
+  the operator to create or chown the host directory.
 - 2026-09-29 variant content types kept in memory (closes #70):
   `Cache.metaCache` holds the content types of up to 10,000 variants in an LRU
   (`github.com/hashicorp/golang-lru/v2`), filled by `StoreVariant` and by
@@ -296,8 +413,8 @@ P2: security: per-IP rate limiting on the image routes
   `ARG VERSION` sits just above the build, so a new version reruns neither
   `script/bootstrap` nor the tests.
 - 2026-09-29 migrations at the path `REPO_POLICIES.md` sets (closes #96): the
-  migration files moved, contents unchanged, from `internal/database/schema/`
-  to `internal/db/migrations/` as `000_migration.sql` and `001_schema.sql`; the
+  migration files moved, contents unchanged, from `internal/database/schema/` to
+  `internal/db/migrations/` as `000_migration.sql` and `001_schema.sql`; the
   `internal/db/migrations` package embeds them and `internal/database` reads
   them through its `FS()`; the `internal/database` package itself stays; the
   version still comes from the filename prefix, so a database that has recorded
@@ -312,8 +429,8 @@ P2: security: per-IP rate limiting on the image routes
   `=` padding kept, and gives the example's `sig` for a stated signing key.
 - 2026-09-29 fixed uid and gid for `pixad` (closes #151): the image creates the
   `pixad` group with gid 65532 and the `pixad` user with uid 65532, instead of
-  the first free uid 1000, so a bind-mounted `/var/lib/pixa` given to `pixad`
-  is not owned on the host by a person's login account; the first-run step of
+  the first free uid 1000, so a bind-mounted `/var/lib/pixa` given to `pixad` is
+  not owned on the host by a person's login account; the first-run step of
   "Running under upaas" in `README.md` names the uid and gid.
 - 2026-09-29 `max-age` never outlives an expiring URL (closes #63): both image
   routes build `Cache-Control` from the request's `Expires`, which an encrypted
@@ -322,29 +439,27 @@ P2: security: per-IP rate limiting on the image routes
   that is sooner, never negative; an allowlisted host's URL that has an `exp`
   follows it too; `immutable` stays, as freshness now ends at the expiry;
   documented in `README.md`.
-- 2026-09-28 add the four settings `README.md` documented but pixa did not
-  have, which aborted startup as unknown keys (closes #61):
+- 2026-09-28 add the four settings `README.md` documented but pixa did not have,
+  which aborted startup as unknown keys (closes #61):
   `access_control_allow_origin` (default `*`, the CORS origin),
   `upstream_fetch_timeout` (default `30s`), `upstream_max_response_size`
-  (default 50 MiB) and `downstream_timeout` (default `60s`, both the
-  server's write timeout and the per-request timeout); each has a
-  `PIXA_` variable; durations are positive Go duration strings, the size a
-  whole number of bytes up to 1 GiB, the origin `*` or one `http` or
-  `https` origin as `README.md` describes it; an invalid value
-  aborts startup naming the key and the value; documented in
-  `config.example.yml` and `README.md`.
-- 2026-09-28 cache stats report real numbers (closes #56): `Cache.Stats`
-  counts the cached source images and processed variants (`source_content`
-  plus `variant_content`) and takes their size from `Cache.UsageBytes`,
-  instead of reading `request_cache` and `output_content`, which nothing
-  writes; those two tables are left in the schema; a disabled disk cache
-  reports no items and no size. A hit is counted even when the request
-  context has ended. A miss is counted after it is served or fails, also
-  when the request context has ended by then, with the bytes it read from
-  upstream, so `upstream_fetch_count` and `upstream_fetch_bytes` move,
-  including for an upstream body that fails partway or a fetched source
-  that then fails the magic byte check; `transform_count` counts each image
-  the image processor transcodes.
+  (default 50 MiB) and `downstream_timeout` (default `60s`, both the server's
+  write timeout and the per-request timeout); each has a `PIXA_` variable;
+  durations are positive Go duration strings, the size a whole number of bytes
+  up to 1 GiB, the origin `*` or one `http` or `https` origin as `README.md`
+  describes it; an invalid value aborts startup naming the key and the value;
+  documented in `config.example.yml` and `README.md`.
+- 2026-09-28 cache stats report real numbers (closes #56): `Cache.Stats` counts
+  the cached source images and processed variants (`source_content` plus
+  `variant_content`) and takes their size from `Cache.UsageBytes`, instead of
+  reading `request_cache` and `output_content`, which nothing writes; those two
+  tables are left in the schema; a disabled disk cache reports no items and no
+  size. A hit is counted even when the request context has ended. A miss is
+  counted after it is served or fails, also when the request context has ended
+  by then, with the bytes it read from upstream, so `upstream_fetch_count` and
+  `upstream_fetch_bytes` move, including for an upstream body that fails partway
+  or a fetched source that then fails the magic byte check; `transform_count`
+  counts each image the image processor transcodes.
 - 2026-09-28 strip metadata from processed images (closes #82): every output is
   exported with govips' `StripMetadata`, so it carries no EXIF, XMP, IPTC or ICC
   profile; the image is first turned upright with `AutoRotate` (before sizes are
@@ -355,220 +470,201 @@ P2: security: per-IP rate limiting on the image routes
   attempts per minute per client address, and an attempt over the limit is
   refused with 429 and a `Retry-After` header; the address is the one
   `internal/clientip` resolves through `trusted_proxies`, an IPv6 client is
-  counted by its /64, and an IPv4-mapped address as the IPv4 address it
-  carries; the limit is a `RateLimit` middleware in `internal/middleware` on
+  counted by its /64, and an IPv4-mapped address as the IPv4 address it carries;
+  the limit is a `RateLimit` middleware in `internal/middleware` on
   `github.com/go-chi/httprate`, which the image routes can reuse; the library
   keeps counts for the current and the previous minute only; documented in
   `README.md`.
-- 2026-09-28 refuse an unparseable `exp` on `/v1/image/` and log swallowed
-  cache errors (closes #72): an `exp` in the URL that is not a whole
-  number, an empty `exp=` included, is a 400 naming `exp` and the value,
-  instead of being ignored and answered with 401 as if the URL had no
-  `exp`; only an `exp` missing from the URL is unchanged; `README.md` says
-  so where it documents `exp`. A failed variant `.meta` write, source
-  metadata JSON write, `Stats` count query, stats counter update, negative
-  cache write or expired negative cache delete is now logged at `warn`
-  with the path or key and the error, and stays non-fatal.
-- 2026-09-28 refuse an empty `fit` on `/v1/image/` (closes #139): a
-  `fit` in the URL with an empty value (`fit=`) is a 400 naming `fit`,
-  instead of being served as `cover` and verified against a signature
-  made for `cover`; only a `fit` missing from the URL is still `cover`;
-  any other value still goes through the existing fit-mode check;
-  `README.md` says so where it documents `fit`.
-- 2026-09-28 refuse an invalid `q` on `/v1/image/` (closes #134): a `q`
-  that is not a whole number from 1 to 100, an empty `q` included, is a
-  400 naming `q` and the value, instead of being served at the default
-  85; the route reads `q` with the generator's quality check
-  (`parseFormInt` with `minQuality` and `maxQuality`); only a `q` missing
-  from the URL is still 85; a query string that cannot be decoded, such
-  as `q=80%`, is a 400 showing it; any query parameter given more than
-  once (`q`, `fit`, `sig`, `exp` alike) is a 400 naming it, so none is
-  read from its first value only; `README.md` states the range and both
-  query-string rules.
-- 2026-09-28 unknown `PIXA_` environment variables abort startup (closes
-  #133): a variable whose name starts with `PIXA_` but is neither a
-  setting's variable nor `PIXA_CONFIG_PATH` aborts startup naming it, as
-  an unknown config key does, and `PIXA_PORT` is named with a pointer to
-  `PORT`; the check runs after the config file loads, so the variables
-  the file's `env:` section sets are checked too; documented in
-  `README.md`.
-- 2026-09-28 start on a fresh upaas volume (closes #129): the image
-  starts as root only to give `/var/lib/pixa` to `pixad` when `pixad`
-  does not own it (`deploy/docker-entrypoint.sh`), then runs the server
-  as `pixad` through `su-exec`, so a root-owned host directory
-  bind-mounted there no longer stops the container at startup;
-  `README.md` gains a "Running under upaas" section.
-- 2026-09-28 run all linting in Docker via `Dockerfile.lint` +
-  `script/lint` (closes #104): `make lint` calls `script/lint`, the only
-  way the linter is run; inside a container (both Dockerfiles set
-  `container=docker`) it runs `golangci-lint`, anywhere else it builds the
-  hash-pinned `Dockerfile.lint`, whose last step runs `script/lint` again;
-  the `Dockerfile` lint stage runs `make lint`; no host or nix-shell
-  `golangci-lint` path remains (`script/bootstrap` installs no linter);
-  a per-run `CACHEBUST` build-arg keeps the lint step from being served
-  from cache, and a tmpfs mount on that step keeps Go's and
-  golangci-lint's caches out of its layer, so a run leaves no large build
-  cache behind; `golangci-lint config verify` stays out, as it fetches its
-  schema over an unpinned live HTTPS call
-- 2026-09-28 every setting as an environment variable (closes #128, also
-  covers #99): each config key can be set by `PIXA_` plus the key in upper
-  case (`.` written as `_`), and the port by `PORT`; a variable present in
-  the environment, even empty, wins over the config file, which wins over
-  the default; the typed getters read the variable first, so every existing
-  check applies to it and a bad value aborts startup naming the variable;
-  lists are comma-separated, and an empty variable (or `""` in the file) is
-  an empty list; the Docker image no longer bakes in `config.docker.yml` or
-  passes `--config`, and its `HEALTHCHECK` probes `PORT` (default `8080`);
-  the config file is looked for under `/etc/pixa` and `~/.config/pixa`
-  instead of the daemon name `pixad`; documented in `README.md` and
-  `config.example.yml`.
-- 2026-09-28 quality and fit in the URL signature (closes #60): the signed
-  data is now `host:path:query:width:height:format:expiration:quality:fit`,
-  using `85` and `cover` when the URL has no `q` or `fit`, so one signed
-  URL can no longer be replayed across other quality and fit values to
-  create unauthorized cache entries and transcodes; the known-answer
-  vectors in `internal/signature/golden_test.go` and the README signature
-  specification describe the new format.
-- 2026-09-28 Docker image healthcheck (closes #111): a `HEALTHCHECK` in
-  the runtime stage probing `/.well-known/healthcheck.json` with busybox
-  `wget`; `script/docker-smoke` (`make docker-smoke`) builds the image,
-  starts it with a throwaway `PIXA_SIGNING_KEY`, and passes only once
-  Docker reports it healthy within 30 seconds, removing the container on
-  exit; the Gitea workflow runs it after `script/cibuild`.
+- 2026-09-28 refuse an unparseable `exp` on `/v1/image/` and log swallowed cache
+  errors (closes #72): an `exp` in the URL that is not a whole number, an empty
+  `exp=` included, is a 400 naming `exp` and the value, instead of being ignored
+  and answered with 401 as if the URL had no `exp`; only an `exp` missing from
+  the URL is unchanged; `README.md` says so where it documents `exp`. A failed
+  variant `.meta` write, source metadata JSON write, `Stats` count query, stats
+  counter update, negative cache write or expired negative cache delete is now
+  logged at `warn` with the path or key and the error, and stays non-fatal.
+- 2026-09-28 refuse an empty `fit` on `/v1/image/` (closes #139): a `fit` in the
+  URL with an empty value (`fit=`) is a 400 naming `fit`, instead of being
+  served as `cover` and verified against a signature made for `cover`; only a
+  `fit` missing from the URL is still `cover`; any other value still goes
+  through the existing fit-mode check; `README.md` says so where it documents
+  `fit`.
+- 2026-09-28 refuse an invalid `q` on `/v1/image/` (closes #134): a `q` that is
+  not a whole number from 1 to 100, an empty `q` included, is a 400 naming `q`
+  and the value, instead of being served at the default 85; the route reads `q`
+  with the generator's quality check (`parseFormInt` with `minQuality` and
+  `maxQuality`); only a `q` missing from the URL is still 85; a query string
+  that cannot be decoded, such as `q=80%`, is a 400 showing it; any query
+  parameter given more than once (`q`, `fit`, `sig`, `exp` alike) is a 400
+  naming it, so none is read from its first value only; `README.md` states the
+  range and both query-string rules.
+- 2026-09-28 unknown `PIXA_` environment variables abort startup (closes #133):
+  a variable whose name starts with `PIXA_` but is neither a setting's variable
+  nor `PIXA_CONFIG_PATH` aborts startup naming it, as an unknown config key
+  does, and `PIXA_PORT` is named with a pointer to `PORT`; the check runs after
+  the config file loads, so the variables the file's `env:` section sets are
+  checked too; documented in `README.md`.
+- 2026-09-28 start on a fresh upaas volume (closes #129): the image starts as
+  root only to give `/var/lib/pixa` to `pixad` when `pixad` does not own it
+  (`deploy/docker-entrypoint.sh`), then runs the server as `pixad` through
+  `su-exec`, so a root-owned host directory bind-mounted there no longer stops
+  the container at startup; `README.md` gains a "Running under upaas" section.
+- 2026-09-28 run all linting in Docker via `Dockerfile.lint` + `script/lint`
+  (closes #104): `make lint` calls `script/lint`, the only way the linter is
+  run; inside a container (both Dockerfiles set `container=docker`) it runs
+  `golangci-lint`, anywhere else it builds the hash-pinned `Dockerfile.lint`,
+  whose last step runs `script/lint` again; the `Dockerfile` lint stage runs
+  `make lint`; no host or nix-shell `golangci-lint` path remains
+  (`script/bootstrap` installs no linter); a per-run `CACHEBUST` build-arg keeps
+  the lint step from being served from cache, and a tmpfs mount on that step
+  keeps Go's and golangci-lint's caches out of its layer, so a run leaves no
+  large build cache behind; `golangci-lint config verify` stays out, as it
+  fetches its schema over an unpinned live HTTPS call
+- 2026-09-28 every setting as an environment variable (closes #128, also covers
+  #99): each config key can be set by `PIXA_` plus the key in upper case (`.`
+  written as `_`), and the port by `PORT`; a variable present in the
+  environment, even empty, wins over the config file, which wins over the
+  default; the typed getters read the variable first, so every existing check
+  applies to it and a bad value aborts startup naming the variable; lists are
+  comma-separated, and an empty variable (or `""` in the file) is an empty list;
+  the Docker image no longer bakes in `config.docker.yml` or passes `--config`,
+  and its `HEALTHCHECK` probes `PORT` (default `8080`); the config file is
+  looked for under `/etc/pixa` and `~/.config/pixa` instead of the daemon name
+  `pixad`; documented in `README.md` and `config.example.yml`.
+- 2026-09-28 quality and fit in the URL signature (closes #60): the signed data
+  is now `host:path:query:width:height:format:expiration:quality:fit`, using
+  `85` and `cover` when the URL has no `q` or `fit`, so one signed URL can no
+  longer be replayed across other quality and fit values to create unauthorized
+  cache entries and transcodes; the known-answer vectors in
+  `internal/signature/golden_test.go` and the README signature specification
+  describe the new format.
+- 2026-09-28 Docker image healthcheck (closes #111): a `HEALTHCHECK` in the
+  runtime stage probing `/.well-known/healthcheck.json` with busybox `wget`;
+  `script/docker-smoke` (`make docker-smoke`) builds the image, starts it with a
+  throwaway `PIXA_SIGNING_KEY`, and passes only once Docker reports it healthy
+  within 30 seconds, removing the container on exit; the Gitea workflow runs it
+  after `script/cibuild`.
 - 2026-09-21 trusted-proxy client IP resolution (closes #94): a
   `trusted_proxies` config key taking a list of CIDRs, parsed by the same
-  `net/netip` list parser as `blocked_networks` (an invalid entry aborts
-  startup naming the key and value; an omitted key defaults to the RFC 1918
-  private ranges, an explicitly empty list trusts no one, and an explicit
-  list replaces the default); a new
-  `internal/clientip` package resolves the client address by honoring
-  `X-Forwarded-For` only when the direct peer is a trusted proxy, walking
-  the chain right-to-left to the rightmost non-proxy entry, so a client
-  connecting directly cannot spoof its address; the resolved address is
-  stored in the request context by a new middleware and used by the
-  request-logging middleware and the login-attempt logs in place of the
-  raw peer address; documented in `README.md` and `config.example.yml`.
+  `net/netip` list parser as `blocked_networks` (an invalid entry aborts startup
+  naming the key and value; an omitted key defaults to the RFC 1918 private
+  ranges, an explicitly empty list trusts no one, and an explicit list replaces
+  the default); a new `internal/clientip` package resolves the client address by
+  honoring `X-Forwarded-For` only when the direct peer is a trusted proxy,
+  walking the chain right-to-left to the rightmost non-proxy entry, so a client
+  connecting directly cannot spoof its address; the resolved address is stored
+  in the request context by a new middleware and used by the request-logging
+  middleware and the login-attempt logs in place of the raw peer address;
+  documented in `README.md` and `config.example.yml`.
 - 2026-09-21 blocked networks configuration extending SSRF protection: a
-  `blocked_networks` config key taking a list of CIDRs (parsed with
-  `net/netip`, an invalid entry aborts startup naming the key and value),
-  added to the built-in blocklist rather than replacing it; the built-in
-  ranges extended to CGNAT `100.64.0.0/10`, IETF protocol assignments
-  `192.0.0.0/24`, benchmark `198.18.0.0/15`, and NAT64 `64:ff9b::/96`
-  (IPv4-mapped forms covered); enforcement stays in the dial-time
-  re-resolution so the DNS-rebinding window remains closed; documented in
-  `README.md` and `config.example.yml`.
-- 2026-09-21 validate dimensions and fit mode on the encrypted-URL
-  route and the token generator (closes #62): `imgcache.ValidateDimension`
-  alone holds the `MaxDimension` bound and is used by the path parser, by
-  the new `ValidateImageRequest` (which also applies `ValidateFitMode`)
-  and by the generator; both the `/v1/image/` and `/v1/e/` routes call
-  `ValidateImageRequest`, so an over-limit size or an unknown fit mode is a
-  400 rather than an out-of-memory or a 500 from the processor; the URL
-  generator answers 400 naming the field for a `width` or `height` that is
-  not a number or fails the shared check, a `quality` that is not a number
-  from 1 to 100, a `ttl` that is not a number from 0 to the largest number
-  of seconds the expiry calculation can hold, or an unknown `fit`; an empty
-  `quality` is 85 and
-  an empty `ttl` never expires; the form's width and height inputs stop at
-  8192
-- 2026-09-21 http.Server hardening (closes #92): added
-  `HTTPReadHeaderTimeout` (10s, bounds the slowloris header dribble) and
-  `HTTPIdleTimeout` (120s, bounds keep-alive reuse) alongside the
-  existing timeouts and wired them onto the server; added a `LimitBody`
-  middleware capping the two form POST bodies (`POST /`, `POST /generate`)
-  at `MaxFormBytes` (1 MiB) and returning 413, applied ahead of the CSRF
-  middleware so an oversized body is refused as 413 rather than being read
-  as a missing CSRF token (403); left `WriteTimeout` at 60s unchanged
-- 2026-08-07 update golangci-lint to v2.12.2 with the canonical
-  `.golangci.yml` (v2 schema, `default: all` minus six disabled
-  linters, `lll` 88, tests included): bumped the pinned
-  `golangci/golangci-lint:v2.12.2-alpine` image in `Dockerfile` and the
-  release-archive sha256 pins in `script/bootstrap`; fixed the findings
-  the stricter config surfaced (notably `paralleltest`, `wsl_v5`,
+  `blocked_networks` config key taking a list of CIDRs (parsed with `net/netip`,
+  an invalid entry aborts startup naming the key and value), added to the
+  built-in blocklist rather than replacing it; the built-in ranges extended to
+  CGNAT `100.64.0.0/10`, IETF protocol assignments `192.0.0.0/24`, benchmark
+  `198.18.0.0/15`, and NAT64 `64:ff9b::/96` (IPv4-mapped forms covered);
+  enforcement stays in the dial-time re-resolution so the DNS-rebinding window
+  remains closed; documented in `README.md` and `config.example.yml`.
+- 2026-09-21 validate dimensions and fit mode on the encrypted-URL route and the
+  token generator (closes #62): `imgcache.ValidateDimension` alone holds the
+  `MaxDimension` bound and is used by the path parser, by the new
+  `ValidateImageRequest` (which also applies `ValidateFitMode`) and by the
+  generator; both the `/v1/image/` and `/v1/e/` routes call
+  `ValidateImageRequest`, so an over-limit size or an unknown fit mode is a 400
+  rather than an out-of-memory or a 500 from the processor; the URL generator
+  answers 400 naming the field for a `width` or `height` that is not a number or
+  fails the shared check, a `quality` that is not a number from 1 to 100, a
+  `ttl` that is not a number from 0 to the largest number of seconds the expiry
+  calculation can hold, or an unknown `fit`; an empty `quality` is 85 and an
+  empty `ttl` never expires; the form's width and height inputs stop at 8192
+- 2026-09-21 http.Server hardening (closes #92): added `HTTPReadHeaderTimeout`
+  (10s, bounds the slowloris header dribble) and `HTTPIdleTimeout` (120s, bounds
+  keep-alive reuse) alongside the existing timeouts and wired them onto the
+  server; added a `LimitBody` middleware capping the two form POST bodies
+  (`POST /`, `POST /generate`) at `MaxFormBytes` (1 MiB) and returning 413,
+  applied ahead of the CSRF middleware so an oversized body is refused as 413
+  rather than being read as a missing CSRF token (403); left `WriteTimeout` at
+  60s unchanged
+- 2026-08-07 update golangci-lint to v2.12.2 with the canonical `.golangci.yml`
+  (v2 schema, `default: all` minus six disabled linters, `lll` 88, tests
+  included): bumped the pinned `golangci/golangci-lint:v2.12.2-alpine` image in
+  `Dockerfile` and the release-archive sha256 pins in `script/bootstrap`; fixed
+  the findings the stricter config surfaced (notably `paralleltest`, `wsl_v5`,
   `goconst`, `lll`, `noinlineerr`, `err113`, `errcheck`, `testpackage` —
-  white-box test files renamed to `*_internal_test.go`), including #55's
-  code absorbed after it merged, iterating the pinned linter to
-  `0 issues.`; no single finding total is substantiable, since
-  golangci-lint's `uniq-by-line` reveals new findings on a line as
-  others there are fixed — the documented re-measurements were 81 after
-  the #53 merge and 149 after the #55 merge; three behavior changes, so
-  not a pure no-op: `Cache.StoreVariant` now takes a `context.Context`
-  (`noctx`), so a cancelled request skips its best-effort accounting
-  row; `MetadataStorage.Store`'s cleanup defer was dead on `main` and
-  leaked `.tmp-*.json` on failure, now fixed with explicit removals; and
-  the `signing_key` validation error text gained `value too short: `;
-  the eviction loop's uncancellable context is deferred to #102 under a
-  `//nolint:contextcheck`; three `//nolint:tagliatelle` directives keep
-  the snake_case JSON wire/disk formats unchanged; `make check` green
-- 2026-08-07 implement cache size management and eviction (closes
-  #51): new `cache_max_bytes` config key validated by the startup
-  framework (explicit values used exactly with no floor, `0` disables
-  the disk cache entirely, omitted defaults to max(75% of free space
-  on the filesystem containing `<state_dir>/cache/`, 500 MiB), logged
-  at startup); processed variants are now tracked in the database (a
-  new `variant_content` table and an LRU timestamp on `source_content`)
-  so total usage is two SUMs, never a directory scan on the hot path; a
-  background goroutine evicts globally least-recently-used entries
-  (variants and source blobs merged) to the limit, woken by a periodic
-  ticker and by write-pressure notifications from stores; a source
-  blob and ALL of its `source_metadata` references are deleted in one
-  transaction before the file is unlinked, so multi-referenced blobs
-  are never removed while referenced and rows never point at deleted
-  files; a startup and periodic reconciliation pass adopts untracked
-  variant files, drops rows for missing files, removes unreachable
-  source blobs, and sweeps stale temp files
-- 2026-08-07 validate configuration on startup, fail fast on bad
-  config (closes #52): a config value that is set but unparseable or
-  invalid aborts startup naming the key and value (defaults apply only
-  to omitted keys), unknown config keys abort startup, a malformed
-  config file aborts instead of being skipped, and `state_dir` is
-  verified creatable and writable before the listener binds
-- 2026-08-07 manual test pass of the auth and encrypted URL flows
-  against a locally built and running `pixad` (built from `main` at
-  `6573b9d`, port 18099, local throwaway config); all six checks
-  passed, plus all nine tests in `scripts/manual-test.sh` (closes #49):
-    - [x] visit `/` and see the login form: HTTP 200, `Pixa - Login`
-      page with `name="key"` password form
-    - [x] wrong key shows an error: POST `/` with `key=wrong-key`
-      returned HTTP 200 login page containing "Invalid signing key"
-    - [x] correct signing key shows the generator form: POST `/`
-      returned HTTP 303 to `/` with
-      `Set-Cookie: pixa_session=...; HttpOnly; Secure; SameSite=Strict`;
-      GET `/` with that cookie rendered `Pixa - URL Generator` with the
+  white-box test files renamed to `*_internal_test.go`), including #55's code
+  absorbed after it merged, iterating the pinned linter to `0 issues.`; no
+  single finding total is substantiable, since golangci-lint's `uniq-by-line`
+  reveals new findings on a line as others there are fixed — the documented
+  re-measurements were 81 after the #53 merge and 149 after the #55 merge; three
+  behavior changes, so not a pure no-op: `Cache.StoreVariant` now takes a
+  `context.Context` (`noctx`), so a cancelled request skips its best-effort
+  accounting row; `MetadataStorage.Store`'s cleanup defer was dead on `main` and
+  leaked `.tmp-*.json` on failure, now fixed with explicit removals; and the
+  `signing_key` validation error text gained `value too short: `; the eviction
+  loop's uncancellable context is deferred to #102 under a
+  `//nolint:contextcheck`; three `//nolint:tagliatelle` directives keep the
+  snake_case JSON wire/disk formats unchanged; `make check` green
+- 2026-08-07 implement cache size management and eviction (closes #51): new
+  `cache_max_bytes` config key validated by the startup framework (explicit
+  values used exactly with no floor, `0` disables the disk cache entirely,
+  omitted defaults to max(75% of free space on the filesystem containing
+  `<state_dir>/cache/`, 500 MiB), logged at startup); processed variants are now
+  tracked in the database (a new `variant_content` table and an LRU timestamp on
+  `source_content`) so total usage is two SUMs, never a directory scan on the
+  hot path; a background goroutine evicts globally least-recently-used entries
+  (variants and source blobs merged) to the limit, woken by a periodic ticker
+  and by write-pressure notifications from stores; a source blob and ALL of its
+  `source_metadata` references are deleted in one transaction before the file is
+  unlinked, so multi-referenced blobs are never removed while referenced and
+  rows never point at deleted files; a startup and periodic reconciliation pass
+  adopts untracked variant files, drops rows for missing files, removes
+  unreachable source blobs, and sweeps stale temp files
+- 2026-08-07 validate configuration on startup, fail fast on bad config (closes
+  #52): a config value that is set but unparseable or invalid aborts startup
+  naming the key and value (defaults apply only to omitted keys), unknown config
+  keys abort startup, a malformed config file aborts instead of being skipped,
+  and `state_dir` is verified creatable and writable before the listener binds
+- 2026-08-07 manual test pass of the auth and encrypted URL flows against a
+  locally built and running `pixad` (built from `main` at `6573b9d`, port 18099,
+  local throwaway config); all six checks passed, plus all nine tests in
+  `scripts/manual-test.sh` (closes #49):
+    - [x] visit `/` and see the login form: HTTP 200, `Pixa - Login` page with
+          `name="key"` password form
+    - [x] wrong key shows an error: POST `/` with `key=wrong-key` returned HTTP
+          200 login page containing "Invalid signing key"
+    - [x] correct signing key shows the generator form: POST `/` returned HTTP
+          303 to `/` with
+          `Set-Cookie: pixa_session=...; HttpOnly; Secure; SameSite=Strict`; GET
+          `/` with that cookie rendered `Pixa - URL Generator` with the
           `/generate` form and logout link
     - [x] a generated encrypted URL serves the image: POST `/generate`
-      (ttl=3600) produced a `/v1/e/<token>/img.jpeg` URL that returned
-      HTTP 200, `Content-Type: image/jpeg`, an 800x600 baseline JPEG of
-      61706 bytes
-    - [x] an expired URL (short TTL) returns 410: a ttl=1 URL fetched
-      after 3 s returned HTTP 410 Gone with
+          (ttl=3600) produced a `/v1/e/<token>/img.jpeg` URL that returned HTTP
+          200, `Content-Type: image/jpeg`, an 800x600 baseline JPEG of 61706
+          bytes
+    - [x] an expired URL (short TTL) returns 410: a ttl=1 URL fetched after 3 s
+          returned HTTP 410 Gone with
           `{"error":"URL has expired","status":410,...}`
-    - [x] logout redirects back to login: GET `/logout` returned HTTP
-      303 to `/` with `Set-Cookie: pixa_session=; Max-Age=0`;
-      subsequent GET `/` rendered the login form again
-- 2026-08-07 fix the two remaining gosec findings (G124 in
-  internal/session): session cookies now always carry
-  Secure/HttpOnly/SameSite=Strict on both the set and clear paths;
-  `make check` green (closes #47)
-- 2026-07-07 Adopted scripts-to-rule-them-all: `script/` entrypoints,
-  Makefile shims, README Entrypoints section
+    - [x] logout redirects back to login: GET `/logout` returned HTTP 303 to `/`
+          with `Set-Cookie: pixa_session=; Max-Age=0`; subsequent GET `/`
+          rendered the login form again
+- 2026-08-07 fix the two remaining gosec findings (G124 in internal/session):
+  session cookies now always carry Secure/HttpOnly/SameSite=Strict on both the
+  set and clear paths; `make check` green (closes #47)
+- 2026-07-07 Adopted scripts-to-rule-them-all: `script/` entrypoints, Makefile
+  shims, README Entrypoints section
 - 2026-04-07 extract magic byte detection into internal/magic (#42)
 - 2026-03-25 extract allowlist package from internal/imgcache (#41)
 - 2026-03-25 move schema_migrations table creation into 000.sql (#36)
-- 2026-03-20 enforce and document exact-match-only signature
-  verification (#40)
-- 2026-03-20 bound imageprocessor.Process input read to prevent
-  unbounded memory use (#37); consolidate appname into an
-  internal/globals constant (#34)
+- 2026-03-20 enforce and document exact-match-only signature verification (#40)
+- 2026-03-20 bound imageprocessor.Process input read to prevent unbounded memory
+  use (#37); consolidate appname into an internal/globals constant (#34)
 - 2026-03-18 parse version prefix from migration filenames (#33)
 - 2026-03-15 QA audit fixes for 1.0/MVP readiness (#25)
-- 2026-03-02 split Dockerfile with pre-built golangci-lint stage for
-  faster CI (#23)
+- 2026-03-02 split Dockerfile with pre-built golangci-lint stage for faster CI
+  (#23)
 - 2026-02-25 repo policy compliance: CI workflow, hash-pinned images,
-  golangci-lint and gosec fixes of that date (#14); arm64 Docker build
-  fix (#16)
-- 2026-01-08 WebP and AVIF encoding support via govips (both former P0
-  image processing items, now done)
+  golangci-lint and gosec fixes of that date (#14); arm64 Docker build fix (#16)
+- 2026-01-08 WebP and AVIF encoding support via govips (both former P0 image
+  processing items, now done)
 
 # Future Steps
 
@@ -576,13 +672,11 @@ P2: security: per-IP rate limiting on the image routes
     - per-origin rate limiting
 - P2: HTTP response handling
     - Last-Modified headers
-    - Vary header for content negotiation
-- P2: auto format selection (format=auto based on Accept header)
 - P2: configuration
     - YAML config file support
 - P2: operational
     - optional Sentry error reporting
     - comprehensive request logging
     - Prometheus performance metrics
-    - integration tests for the image proxy flow
-    - load tests to verify the 1k to 5k req/s target
+    - measure the 1k to 5k req/s target with `script/loadtest` on a machine not
+      shared with other work

cmd/loadtest-origin/main.go

@@ -0,0 +1,9 @@
+// Command loadtest-origin is the upstream host script/loadtest points pixad
+// at; internal/loadtestorigin says what it does.
+package main
+
+import "sneak.berlin/go/pixa/internal/loadtestorigin"
+
+func main() {
+	loadtestorigin.Run()
+}

cmd/pixad/main.go

@@ -1,69 +1,10 @@
 // Package main is the entry point for the pixad image proxy server.
 package main
 
-import (
-	"fmt"
-	"os"
-	"os/signal"
-	"syscall"
-
-	"github.com/spf13/cobra"
-	"go.uber.org/fx"
-	"sneak.berlin/go/pixa/internal/config"
-	"sneak.berlin/go/pixa/internal/database"
-	"sneak.berlin/go/pixa/internal/globals"
-	"sneak.berlin/go/pixa/internal/handlers"
-	"sneak.berlin/go/pixa/internal/healthcheck"
-	"sneak.berlin/go/pixa/internal/logger"
-	"sneak.berlin/go/pixa/internal/middleware"
-	"sneak.berlin/go/pixa/internal/server"
-)
+import "sneak.berlin/go/pixa/internal/app"
 
 var Version string //nolint:gochecknoglobals // set by ldflags
 
-var configPath string //nolint:gochecknoglobals // cobra flag
-
 func main() {
-	rootCmd := &cobra.Command{
-		Use:   "pixad",
-		Short: "Pixa image caching proxy server",
-		Run:   run,
-	}
-
-	rootCmd.Flags().StringVarP(&configPath, "config", "c", "", "path to config file")
-
-	err := rootCmd.Execute()
-	if err != nil {
-		fmt.Fprintln(os.Stderr, err)
-		os.Exit(1)
-	}
-}
-
-func run(_ *cobra.Command, _ []string) {
-	globals.Version = Version
-
-	// Set config path in environment if specified via flag
-	if configPath != "" {
-		_ = os.Setenv("PIXA_CONFIG_PATH", configPath)
-	}
-
-	// A write to a closed stdout or stderr must not end the process.
-	signal.Ignore(syscall.SIGPIPE)
-
-	fx.New(
-		fx.Provide(
-			config.New,
-			database.New,
-			globals.New,
-			handlers.New,
-			logger.New,
-			server.New,
-			middleware.New,
-			healthcheck.New,
-		),
-		fx.Invoke(
-			func(log *logger.Logger) { log.Identify() },
-			func(*server.Server) {},
-		),
-	).Run()
+	app.Run(Version)
 }

internal/app/app.go

@@ -0,0 +1,70 @@
+// Package app reads the pixad command line and runs the server.
+package app
+
+import (
+	"fmt"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"github.com/spf13/cobra"
+	"go.uber.org/fx"
+	"sneak.berlin/go/pixa/internal/config"
+	"sneak.berlin/go/pixa/internal/database"
+	"sneak.berlin/go/pixa/internal/globals"
+	"sneak.berlin/go/pixa/internal/handlers"
+	"sneak.berlin/go/pixa/internal/healthcheck"
+	"sneak.berlin/go/pixa/internal/logger"
+	"sneak.berlin/go/pixa/internal/middleware"
+	"sneak.berlin/go/pixa/internal/server"
+)
+
+var configPath string //nolint:gochecknoglobals // cobra flag
+
+// Run reads the command line and runs the server until it stops, with
+// version as the version pixad logs and reports. It exits the process
+// with status 1 when the command line is not valid.
+func Run(version string) {
+	globals.Version = version
+
+	rootCmd := &cobra.Command{
+		Use:   "pixad",
+		Short: "Pixa image caching proxy server",
+		Run:   run,
+	}
+
+	rootCmd.Flags().StringVarP(&configPath, "config", "c", "", "path to config file")
+
+	err := rootCmd.Execute()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+
+func run(_ *cobra.Command, _ []string) {
+	// Set config path in environment if specified via flag
+	if configPath != "" {
+		_ = os.Setenv("PIXA_CONFIG_PATH", configPath)
+	}
+
+	// A write to a closed stdout or stderr must not end the process.
+	signal.Ignore(syscall.SIGPIPE)
+
+	fx.New(
+		fx.Provide(
+			config.New,
+			database.New,
+			globals.New,
+			handlers.New,
+			logger.New,
+			server.New,
+			middleware.New,
+			healthcheck.New,
+		),
+		fx.Invoke(
+			func(log *logger.Logger) { log.Identify() },
+			func(*server.Server) {},
+		),
+	).Run()
+}

internal/globals/globals.go

@@ -7,8 +7,8 @@ import (
 
 const appname = "pixad"
 
-// Version is populated from main() via ldflags.
-var Version string //nolint:gochecknoglobals // set from main
+// Version is set by app.Run to the version main was built with.
+var Version string //nolint:gochecknoglobals // set by app.Run
 
 // Globals holds application-wide constants.
 type Globals struct {

internal/handlers/auth.go

@@ -371,7 +371,7 @@ func (s *Handlers) buildGeneratedURL(r *http.Request, token, format string) stri
 
 	// Determine file extension for the trailing filename
 	ext := format
-	if ext == "" || ext == "orig" {
+	if ext == "" || ext == "orig" || ext == "auto" {
 		ext = "jpg" // Default extension
 	}
 

internal/handlers/auth_session_internal_test.go

@@ -8,6 +8,7 @@ import (
 	"regexp"
 	"strings"
 	"testing"
+	"time"
 
 	"sneak.berlin/go/pixa/internal/imgcache"
 	"sneak.berlin/go/pixa/internal/session"
@@ -241,3 +242,51 @@ func TestGeneratePost_URLServesImage(t *testing.T) {
 
 	requireServedPhoto(t, imageRec)
 }
+
+// TestGeneratePost_URLWithTTLExpires verifies that a URL the generator page
+// makes with a ttl of one second is served by /v1/e/ at once and answers 410
+// once the ttl has passed.
+func TestGeneratePost_URLWithTTLExpires(t *testing.T) {
+	t.Parallel()
+
+	_, imageSrv := newSignedHostServer(t, slog.New(slog.DiscardHandler))
+
+	rec := generatePost(t, url.Values{
+		sourceURLField: {"https://" + signedHost + photoPath},
+		widthField:     {"50"},
+		heightField:    {"50"},
+		formatField:    {string(imgcache.FormatJPEG)},
+		ttlField:       {"1"},
+	})
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("POST /generate status = %d, want %d", rec.Code, http.StatusOK)
+	}
+
+	match := generatedURLPattern.FindStringSubmatch(rec.Body.String())
+	if match == nil {
+		t.Fatalf("generator page shows no URL: %s", rec.Body.String())
+	}
+
+	imageRec := httptest.NewRecorder()
+	imageSrv.ServeHTTP(imageRec, httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, match[1], nil))
+
+	requireServedPhoto(t, imageRec)
+
+	// The URL keeps the time it expires in whole seconds and is served
+	// through the whole of that second, so a ttl of one second has passed
+	// for certain two seconds after the URL was made.
+	time.Sleep(2 * time.Second)
+
+	imageRec = httptest.NewRecorder()
+	imageSrv.ServeHTTP(imageRec, httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, match[1], nil))
+
+	t.Logf("GET %s after the ttl: %d %q", match[1], imageRec.Code, imageRec.Body)
+
+	if imageRec.Code != http.StatusGone {
+		t.Errorf("status after the ttl = %d, want %d",
+			imageRec.Code, http.StatusGone)
+	}
+}

internal/handlers/fetcher_internal_test.go

@@ -0,0 +1,61 @@
+package handlers
+
+import (
+	"net/http"
+	"net/netip"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+	"go.uber.org/fx"
+	"go.uber.org/fx/fxtest"
+
+	"sneak.berlin/go/pixa/internal/config"
+	"sneak.berlin/go/pixa/internal/database"
+	"sneak.berlin/go/pixa/internal/globals"
+	"sneak.berlin/go/pixa/internal/healthcheck"
+	"sneak.berlin/go/pixa/internal/logger"
+)
+
+// TestHandlersBuildTheirOwnFetcherWhenNoneIsProvided builds the handlers as
+// pixad does, in an fx app that provides no fetcher, and requests an image
+// from 192.0.2.10, which is on the allowlist and in blocked_networks. The URL
+// check accepts that address; only the dialer that refuses internal
+// addresses checks blocked_networks, so the answer is 403 only if the
+// fetcher the handlers build from the config connects with that dialer. Any
+// other dialer would try to connect until the upstream fetch timeout, which
+// is short so that the test then fails quickly.
+func TestHandlersBuildTheirOwnFetcherWhenNoneIsProvided(t *testing.T) {
+	t.Parallel()
+
+	const host = "192.0.2.10"
+
+	stateDir := t.TempDir()
+	cfg := &config.Config{
+		SigningKey:           testSigningKey,
+		StateDir:             stateDir,
+		DBURL:                "file:" + filepath.Join(stateDir, "state.sqlite3"),
+		AllowlistHosts:       []string{host},
+		BlockedNetworks:      []netip.Prefix{netip.MustParsePrefix("192.0.2.0/24")},
+		UpstreamFetchTimeout: 2 * time.Second,
+		// With no connection slots, the fetch would fail before dialing.
+		UpstreamConnections: config.DefaultUpstreamConnections,
+	}
+
+	var h *Handlers
+
+	app := fxtest.New(t,
+		fx.Supply(cfg),
+		fx.Provide(globals.New, logger.New, database.New, healthcheck.New, New),
+		fx.Populate(&h),
+	)
+	app.RequireStart()
+	t.Cleanup(app.RequireStop)
+
+	r := chi.NewRouter()
+	r.Get("/v1/image/*", h.HandleImage())
+
+	rec := sendGet(t, r, photoURL(host))
+	checkErrorBody(t, rec, http.StatusForbidden, "forbidden")
+}

internal/handlers/format_auto.go

@@ -0,0 +1,131 @@
+package handlers
+
+import (
+	"errors"
+	"fmt"
+	"mime"
+	"net/http"
+	"strconv"
+	"strings"
+
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// Errors for an Accept header that an auto URL cannot be served for.
+var (
+	errInvalidAccept = errors.New("invalid Accept header")
+	errNotAcceptable = errors.New(
+		"not acceptable: auto serves image/avif, image/webp or image/jpeg")
+)
+
+// chooseAutoFormat replaces the format auto in req with the format
+// formatForAccept chooses from r's Accept header, and adds Vary: Accept to the
+// response, which then depends on that header. It answers 400 for an Accept
+// header that is not valid and 406 for one that allows none of the formats,
+// and reports whether req can be served. Any other format is left as it is.
+func (s *Handlers) chooseAutoFormat(
+	w http.ResponseWriter, r *http.Request, req *imgcache.ImageRequest,
+) bool {
+	if req.Format != imgcache.FormatAuto {
+		return true
+	}
+
+	w.Header().Add("Vary", "Accept")
+
+	format, err := formatForAccept(strings.Join(r.Header.Values("Accept"), ","))
+	if errors.Is(err, errNotAcceptable) {
+		s.respondError(w, err.Error(), http.StatusNotAcceptable)
+
+		return false
+	}
+
+	if err != nil {
+		s.respondError(w, err.Error(), http.StatusBadRequest)
+
+		return false
+	}
+
+	req.Format = format
+
+	return true
+}
+
+// formatForAccept returns the format an auto URL is served in for the Accept
+// header accept: AVIF when it names image/avif, else WebP when it names
+// image/webp, else JPEG when its most specific entry of image/jpeg, image/*
+// and */* allows it, or when it names nothing. A q of 0 refuses a format.
+// AVIF and WebP must be named, as clients that cannot show them send image/*
+// and */* too.
+func formatForAccept(accept string) (imgcache.ImageFormat, error) {
+	qualities, err := parseAccept(accept)
+	if err != nil {
+		return "", err
+	}
+
+	if len(qualities) == 0 {
+		return imgcache.FormatJPEG, nil
+	}
+
+	if qualities["image/avif"] > 0 {
+		return imgcache.FormatAVIF, nil
+	}
+
+	if qualities["image/webp"] > 0 {
+		return imgcache.FormatWebP, nil
+	}
+
+	// For JPEG, the most specific entry the header has decides
+	quality, named := qualities["image/jpeg"]
+	if !named {
+		quality, named = qualities["image/*"]
+	}
+
+	if !named {
+		quality = qualities["*/*"]
+	}
+
+	if quality > 0 {
+		return imgcache.FormatJPEG, nil
+	}
+
+	return "", errNotAcceptable
+}
+
+// parseAccept returns the q of each media range the Accept header accept
+// names, 1 where it gives none. A media range named more than once keeps its
+// lowest q, so a refusal is never overridden. A media range that does not
+// parse, or a q that is not a number from 0 to 1, is an error.
+func parseAccept(accept string) (map[string]float64, error) {
+	qualities := make(map[string]float64)
+
+	for entry := range strings.SplitSeq(accept, ",") {
+		// A header field list may hold empty entries
+		if strings.TrimSpace(entry) == "" {
+			continue
+		}
+
+		mediaRange, params, err := mime.ParseMediaType(entry)
+		if err != nil {
+			return nil, fmt.Errorf("%w: %q: %w", errInvalidAccept, entry, err)
+		}
+
+		quality := 1.0
+
+		if qParam, given := params["q"]; given {
+			quality, err = strconv.ParseFloat(qParam, 64)
+			inRange := quality >= 0 && quality <= 1
+
+			if err != nil || !inRange {
+				return nil, fmt.Errorf("%w: %q: q is not a number from 0 to 1",
+					errInvalidAccept, entry)
+			}
+		}
+
+		previous, named := qualities[mediaRange]
+		if !named || quality < previous {
+			qualities[mediaRange] = quality
+		}
+	}
+
+	return qualities, nil
+}

internal/handlers/format_auto_internal_test.go

@@ -0,0 +1,310 @@
+package handlers
+
+import (
+	"errors"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"slices"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+
+	"sneak.berlin/go/pixa/internal/encurl"
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// The content types the tests below expect.
+const (
+	avifType = "image/avif"
+	webpType = "image/webp"
+	jpegType = "image/jpeg"
+	jsonType = "application/json"
+)
+
+// TestFormatForAccept verifies the format chosen for the format auto from each
+// Accept header below, and the error for one that allows none of AVIF, WebP
+// and JPEG or is not valid.
+func TestFormatForAccept(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name    string
+		accept  string
+		want    imgcache.ImageFormat
+		wantErr error
+	}{
+		{"AVIF-capable browser",
+			"image/avif,image/webp,image/apng,image/svg+xml,image/*,*/*;q=0.8",
+			imgcache.FormatAVIF, nil},
+		{"WebP-capable browser",
+			"image/webp,image/png,image/svg+xml,image/*;q=0.8,*/*;q=0.5",
+			imgcache.FormatWebP, nil},
+		{"WebP only", webpType, imgcache.FormatWebP, nil},
+		{"neither", "image/png,image/*;q=0.8,*/*;q=0.5", imgcache.FormatJPEG, nil},
+		{"wildcard only", "*/*", imgcache.FormatJPEG, nil},
+		{"image wildcard only", "image/*", imgcache.FormatJPEG, nil},
+		{"absent", "", imgcache.FormatJPEG, nil},
+		{"q=0 on AVIF", "image/avif;q=0,image/webp,*/*", imgcache.FormatWebP, nil},
+		{"AVIF named twice, once with q=0", "image/avif,image/avif;q=0.0,*/*",
+			imgcache.FormatJPEG, nil},
+		{"upper case and spaces", " Image/AVIF ; Q=0.5 ", imgcache.FormatAVIF, nil},
+		{"q=0 on JPEG", "image/jpeg;q=0,image/*", "", errNotAcceptable},
+		{"q=0 on everything", "*/*;q=0", "", errNotAcceptable},
+		{"PNG only", "image/png", "", errNotAcceptable},
+		{"malformed media range", "image/", "", errInvalidAccept},
+		{"q not a number", "image/avif;q=high", "", errInvalidAccept},
+		{"q above 1", "image/avif;q=2", "", errInvalidAccept},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			got, err := formatForAccept(tt.accept)
+			t.Logf("Accept %q: %q, %v", tt.accept, got, err)
+
+			if got != tt.want || !errors.Is(err, tt.wantErr) {
+				t.Errorf("formatForAccept(%q) = %q, %v, want %q, %v",
+					tt.accept, got, err, tt.want, tt.wantErr)
+			}
+		})
+	}
+}
+
+// autoPhotoURLs returns a signed /v1/image/ URL and an encrypted /v1/e/ URL,
+// both valid for a minute, for the JPEG at photoPath on signedHost at 50x50 in
+// the format auto, made with h's image service and generator.
+func autoPhotoURLs(t *testing.T, h *Handlers) (string, string) {
+	t.Helper()
+
+	signedURL, err := h.imgSvc.GenerateSignedURL("", &imgcache.ImageRequest{
+		SourceHost: signedHost,
+		SourcePath: photoPath,
+		Size:       imgcache.Size{Width: 50, Height: 50},
+		Format:     imgcache.FormatAuto,
+	}, time.Minute)
+	if err != nil {
+		t.Fatalf("GenerateSignedURL() error = %v", err)
+	}
+
+	token, err := h.encGen.Generate(&encurl.Payload{
+		SourceHost: signedHost,
+		SourcePath: photoPath,
+		Width:      50,
+		Height:     50,
+		Format:     imgcache.FormatAuto,
+		ExpiresAt:  time.Now().Add(time.Minute).Unix(),
+	})
+	if err != nil {
+		t.Fatalf("Generate() error = %v", err)
+	}
+
+	return signedURL, "/v1/e/" + token + "/img.jpg"
+}
+
+// requestImage sends method for target to srv with an Accept header line for
+// each of accept, and returns the response.
+func requestImage(
+	t *testing.T, srv http.Handler, method, target string, accept ...string,
+) *httptest.ResponseRecorder {
+	t.Helper()
+
+	req := httptest.NewRequestWithContext(t.Context(), method, target, nil)
+
+	for _, value := range accept {
+		req.Header.Add("Accept", value)
+	}
+
+	rec := httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+	t.Logf("%s %s with Accept %q: %d, Content-Type %s, Vary %v, X-Pixa-Cache %s",
+		method, target, accept, rec.Code, rec.Header().Get("Content-Type"),
+		rec.Header().Values("Vary"), rec.Header().Get("X-Pixa-Cache"))
+
+	return rec
+}
+
+// TestFormatAuto_ChosenFromAccept requests an auto URL on each image route
+// with each Accept below, and checks the answer and that it carries
+// Vary: Accept. The signed URL is signed for auto, so it is valid whatever
+// Accept chooses.
+func TestFormatAuto_ChosenFromAccept(t *testing.T) {
+	t.Parallel()
+
+	h, srv := newSignedHostServer(t, slog.New(slog.DiscardHandler))
+	signedURL, encryptedURL := autoPhotoURLs(t, h)
+
+	tests := []struct {
+		name       string
+		accept     []string
+		wantStatus int
+		wantType   string
+	}{
+		{"AVIF accepted", []string{"image/avif,image/webp,*/*;q=0.8"},
+			http.StatusOK, avifType},
+		{"WebP accepted", []string{"image/webp,*/*;q=0.8"}, http.StatusOK, webpType},
+		{"no Accept", nil, http.StatusOK, jpegType},
+		{"two Accept lines", []string{"image/png", webpType}, http.StatusOK, webpType},
+		{"none of the three", []string{"image/gif"},
+			http.StatusNotAcceptable, jsonType},
+		{"not valid", []string{"image/avif;q=high"}, http.StatusBadRequest, jsonType},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			for _, target := range []string{signedURL, encryptedURL} {
+				rec := requestImage(t, srv, http.MethodGet, target, tt.accept...)
+				gotType := rec.Header().Get("Content-Type")
+
+				if rec.Code != tt.wantStatus || gotType != tt.wantType {
+					t.Errorf("%s: %d %s, want %d %s; body %s", target,
+						rec.Code, gotType, tt.wantStatus, tt.wantType, rec.Body)
+				}
+
+				if !slices.Contains(rec.Header().Values("Vary"), "Accept") {
+					t.Errorf("%s: Vary = %v, want Accept in it",
+						target, rec.Header().Values("Vary"))
+				}
+			}
+		})
+	}
+}
+
+// TestFormatAuto_SignatureCoversAuto verifies that a /v1/image/ URL with the
+// format auto is checked against a signature for auto, not for the format
+// chosen: a URL signed for avif, with auto put in its path, is refused for a
+// client whose Accept chooses AVIF.
+func TestFormatAuto_SignatureCoversAuto(t *testing.T) {
+	t.Parallel()
+
+	h, srv := newSignedHostServer(t, slog.New(slog.DiscardHandler))
+
+	signedForAVIF, err := h.imgSvc.GenerateSignedURL("", &imgcache.ImageRequest{
+		SourceHost: signedHost,
+		SourcePath: photoPath,
+		Size:       imgcache.Size{Width: 50, Height: 50},
+		Format:     imgcache.FormatAVIF,
+	}, time.Minute)
+	if err != nil {
+		t.Fatalf("GenerateSignedURL() error = %v", err)
+	}
+
+	target := strings.Replace(signedForAVIF, "/50x50.avif?", "/50x50.auto?", 1)
+	if target == signedForAVIF {
+		t.Fatalf("no /50x50.avif? in %s", signedForAVIF)
+	}
+
+	rec := requestImage(t, srv, http.MethodGet, target, avifType)
+	if rec.Code != http.StatusUnauthorized {
+		t.Errorf("status = %d, want %d", rec.Code, http.StatusUnauthorized)
+	}
+}
+
+// TestFormatAuto_CachesEachFormatApart requests an auto URL for AVIF, then
+// JPEG, then both again. Each format is processed once and then served from
+// the cache, with an ETag of its own, so a client never gets the other format
+// from the cache.
+func TestFormatAuto_CachesEachFormatApart(t *testing.T) {
+	t.Parallel()
+
+	h, srv := newSignedHostServer(t, slog.New(slog.DiscardHandler))
+	signedURL, _ := autoPhotoURLs(t, h)
+
+	steps := []struct {
+		wantType  string
+		wantCache string
+	}{
+		{avifType, "MISS"},
+		{jpegType, "MISS"},
+		{avifType, "HIT"},
+		{jpegType, "HIT"},
+	}
+
+	etags := make(map[string]string)
+
+	for _, step := range steps {
+		rec := requestImage(t, srv, http.MethodGet, signedURL, step.wantType)
+		gotType := rec.Header().Get("Content-Type")
+		gotCache := rec.Header().Get("X-Pixa-Cache")
+
+		if rec.Code != http.StatusOK || gotType != step.wantType ||
+			gotCache != step.wantCache {
+			t.Fatalf("Accept %s: %d %s %s, want 200 %s %s", step.wantType,
+				rec.Code, gotType, gotCache, step.wantType, step.wantCache)
+		}
+
+		etag := rec.Header().Get("ETag")
+		if previous, seen := etags[gotType]; seen && previous != etag {
+			t.Errorf("%s ETag changed from %s to %s", gotType, previous, etag)
+		}
+
+		etags[gotType] = etag
+	}
+
+	if etags[avifType] == etags[jpegType] {
+		t.Errorf("AVIF and JPEG have the same ETag %s", etags[avifType])
+	}
+}
+
+// TestFormatAuto_Vary verifies that on each image route a HEAD answer and a
+// 304 for an auto URL carry Vary: Accept, and that the answer for a URL with
+// a fixed format does not.
+func TestFormatAuto_Vary(t *testing.T) {
+	t.Parallel()
+
+	h, _ := newSignedHostServer(t, slog.New(slog.DiscardHandler))
+
+	srv := chi.NewRouter()
+	srv.Get("/v1/image/*", h.HandleImage())
+	srv.Head("/v1/image/*", h.HandleImage())
+	srv.Get("/v1/e/{token}/*", h.HandleImageEnc())
+	srv.Head("/v1/e/{token}/*", h.HandleImageEnc())
+
+	signedURL, encryptedURL := autoPhotoURLs(t, h)
+
+	for _, urls := range [][2]string{
+		{signedURL, signedPhotoURL(t, h)},
+		{encryptedURL, encPhotoURL(t, h)},
+	} {
+		autoURL, fixedURL := urls[0], urls[1]
+
+		head := requestImage(t, srv, http.MethodHead, autoURL, webpType)
+		checkVaryAccept(t, head, http.StatusOK, true)
+
+		req := httptest.NewRequestWithContext(t.Context(), http.MethodGet,
+			autoURL, nil)
+		req.Header.Set("Accept", webpType)
+		req.Header.Set("If-None-Match", head.Header().Get("ETag"))
+
+		notModified := httptest.NewRecorder()
+		srv.ServeHTTP(notModified, req)
+		checkVaryAccept(t, notModified, http.StatusNotModified, true)
+
+		fixed := requestImage(t, srv, http.MethodGet, fixedURL)
+		checkVaryAccept(t, fixed, http.StatusOK, false)
+	}
+}
+
+// checkVaryAccept fails the test unless rec answered wantStatus and, as
+// wantVary says, has or has not Accept in its Vary header.
+func checkVaryAccept(
+	t *testing.T, rec *httptest.ResponseRecorder, wantStatus int, wantVary bool,
+) {
+	t.Helper()
+
+	vary := rec.Header().Values("Vary")
+	t.Logf("status %d, Vary %v", rec.Code, vary)
+
+	if rec.Code != wantStatus {
+		t.Errorf("status = %d, want %d", rec.Code, wantStatus)
+	}
+
+	if slices.Contains(vary, "Accept") != wantVary {
+		t.Errorf("Vary = %v, want Accept in it: %v", vary, wantVary)
+	}
+}

internal/handlers/handlers.go

@@ -28,6 +28,11 @@ type Params struct {
 	Healthcheck *healthcheck.Healthcheck
 	Database    *database.Database
 	Config      *config.Config
+
+	// Fetcher, when provided, fetches upstream images in place of the
+	// fetcher the handlers build from the config. Only tests provide one;
+	// pixad does not.
+	Fetcher httpfetcher.Fetcher `optional:"true"`
 }
 
 // Handlers provides HTTP request handlers.
@@ -36,6 +41,7 @@ type Handlers struct {
 	hc          *healthcheck.Healthcheck
 	db          *database.Database
 	config      *config.Config
+	fetcher     httpfetcher.Fetcher
 	imgSvc      *imgcache.Service
 	imgCache    *imgcache.Cache
 	sessMgr     *session.Manager
@@ -59,6 +65,7 @@ func New(lc fx.Lifecycle, params Params) (*Handlers, error) {
 		hc:               params.Healthcheck,
 		db:               params.Database,
 		config:           params.Config,
+		fetcher:          params.Fetcher,
 		csrfProtect:      csrfProtect,
 		refererBlocklist: allowlist.New(params.Config.RefererBlocklist),
 	}
@@ -128,10 +135,12 @@ func (s *Handlers) initImageService() error {
 	fetcherCfg.MaxConnections = s.config.UpstreamConnections
 	fetcherCfg.BlockedNetworks = s.config.BlockedNetworks
 
-	// Create the service
+	// Create the service. With no fetcher provided, it builds its own from
+	// fetcherCfg.
 	svc, err := imgcache.NewService(&imgcache.ServiceConfig{
 		Cache:                   cache,
 		FetcherConfig:           fetcherCfg,
+		Fetcher:                 s.fetcher,
 		SigningKey:              s.config.SigningKey,
 		Allowlist:               s.config.AllowlistHosts,
 		MaxConcurrentProcessing: s.config.MaxConcurrentProcessing,

internal/handlers/image.go

@@ -43,6 +43,11 @@ func (s *Handlers) HandleImage() http.HandlerFunc {
 			return
 		}
 
+		// The signature covers the format auto, not the format chosen
+		if !s.chooseAutoFormat(w, r, req) {
+			return
+		}
+
 		// Get cache key for logging
 		cacheKey := imgcache.CacheKey(req)
 

internal/handlers/imageenc.go

@@ -30,7 +30,7 @@ func (s *Handlers) HandleImageEnc() http.HandlerFunc {
 		start := time.Now()
 
 		req, ok := s.parseImageEncRequest(w, r)
-		if !ok {
+		if !ok || !s.chooseAutoFormat(w, r, req) {
 			return
 		}
 

internal/httpfetcher/dial_context_internal_test.go

@@ -0,0 +1,66 @@
+package httpfetcher
+
+import (
+	"errors"
+	"net"
+	"testing"
+)
+
+// TestNewUsesCheckedDialerWithoutDialContext checks that a fetcher built
+// without DialContext, as pixa builds it, refuses to connect to a local
+// server.
+func TestNewUsesCheckedDialerWithoutDialContext(t *testing.T) {
+	t.Parallel()
+
+	srv := startUpstream(t)
+	transport := transportOf(t, New(DefaultConfig()))
+
+	addr := srv.Listener.Addr().String()
+
+	_, err := transport.DialContext(testContext(t), "tcp", addr)
+	if !errors.Is(err, ErrSSRFBlocked) {
+		t.Fatalf("DialContext(%s) error = %v, want ErrSSRFBlocked", addr, err)
+	}
+}
+
+// TestDialContextReplacesOnlyTheDialer checks that a fetcher built with
+// DialContext connects through it, while the URL check still refuses a
+// loopback URL and the redirect check a redirect to a link-local address.
+func TestDialContextReplacesOnlyTheDialer(t *testing.T) {
+	t.Parallel()
+
+	srv := startUpstream(t)
+	dialer := &recordingDialer{target: srv.Listener.Addr().String()}
+
+	cfg := DefaultConfig()
+	cfg.AllowHTTP = true
+	cfg.DialContext = dialer.dialContext
+	f := New(cfg)
+
+	if body := fetchBody(t, f, "/image"); body != imagePayload {
+		t.Errorf("body = %q, want %q", body, imagePayload)
+	}
+
+	_, err := f.Fetch(testContext(t), "http://127.0.0.1/image")
+	if !errors.Is(err, ErrSSRFBlocked) {
+		t.Errorf("Fetch(loopback URL) error = %v, want ErrSSRFBlocked", err)
+	}
+
+	_, err = f.Fetch(testContext(t), upstreamURL("/redirect/private"))
+	if !errors.Is(err, ErrSSRFBlocked) {
+		t.Errorf("Fetch(/redirect/private) error = %v, want ErrSSRFBlocked", err)
+	}
+
+	// The upstream server is reached through DialContext, and nothing else
+	// is asked of it.
+	dialed := dialer.dialedAddrs()
+	if len(dialed) == 0 {
+		t.Error("DialContext was never called")
+	}
+
+	for _, addr := range dialed {
+		if addr != net.JoinHostPort(testPublicHost, "80") {
+			t.Errorf("DialContext was asked to connect to %s", addr)
+		}
+	}
+}

internal/httpfetcher/httpfetcher.go

@@ -137,6 +137,11 @@ type Config struct {
 	// BlockedNetworks are operator-supplied CIDR ranges refused by the
 	// dialer, in addition to the always-enforced built-in ranges.
 	BlockedNetworks []netip.Prefix
+	// DialContext, when set, makes the fetcher's connections in place of
+	// the dialer that refuses internal addresses; the URL and redirect
+	// checks still run. Only tests set it, to reach a local server; the
+	// config file and the environment cannot.
+	DialContext func(ctx context.Context, network, addr string) (net.Conn, error)
 }
 
 // DefaultConfig returns a Config with sensible defaults.
@@ -190,13 +195,19 @@ func New(config *Config) *HTTPFetcher {
 		config = DefaultConfig()
 	}
 
-	// Create transport with SSRF-safe dialer. The dialer re-resolves and
-	// re-checks at connect time (closing the DNS-rebinding window) against
-	// both the built-in ranges and the operator-supplied blocklist.
-	transport := &http.Transport{
-		DialContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
+	// Unless config.DialContext replaces it, the transport connects with
+	// the SSRF-safe dialer, which re-resolves and re-checks at connect time
+	// (closing the DNS-rebinding window) against both the built-in ranges
+	// and the operator-supplied blocklist.
+	dialContext := config.DialContext
+	if dialContext == nil {
+		dialContext = func(ctx context.Context, network, addr string) (net.Conn, error) {
 			return dialSSRFSafe(ctx, network, addr, config.BlockedNetworks)
-		},
+		}
+	}
+
+	transport := &http.Transport{
+		DialContext:         dialContext,
 		TLSHandshakeTimeout: DefaultTLSTimeout,
 		MaxIdleConns:        DefaultMaxIdleConns,
 		IdleConnTimeout:     DefaultIdleConnTimeout,

internal/imgcache/imgcache.go

@@ -22,6 +22,11 @@ const (
 	FormatWebP     ImageFormat = "webp"
 	FormatAVIF     ImageFormat = "avif"
 	FormatGIF      ImageFormat = "gif"
+
+	// FormatAuto stands for AVIF, WebP or JPEG, chosen for each request
+	// from its Accept header once the URL's signature or token has been
+	// checked; it is never processed or cached as itself.
+	FormatAuto ImageFormat = "auto"
 )
 
 // Size represents requested image dimensions

internal/imgcache/service.go

@@ -42,7 +42,8 @@ type Service struct {
 type ServiceConfig struct {
 	// Cache is the cache instance
 	Cache *Cache
-	// FetcherConfig configures the upstream fetcher (ignored if Fetcher is set)
+	// FetcherConfig configures the upstream fetcher built when Fetcher is
+	// not set. Its AllowHTTP and MaxResponseSize are used either way.
 	FetcherConfig *httpfetcher.Config
 	// Fetcher is an optional custom fetcher (for testing)
 	Fetcher httpfetcher.Fetcher

internal/imgcache/urlparser.go

@@ -277,6 +277,8 @@ func parseFormat(s string) (ImageFormat, error) {
 		return FormatAVIF, nil
 	case "gif":
 		return FormatGIF, nil
+	case "auto":
+		return FormatAuto, nil
 	default:
 		return "", fmt.Errorf("%w: %s", ErrInvalidFormat, s)
 	}

internal/imgcache/urlparser_internal_test.go

@@ -111,6 +111,21 @@ func TestParseImageURL(t *testing.T) {
 	}
 }
 
+// TestParseImageURL_AutoFormat verifies that the format auto in an image URL
+// parses as FormatAuto.
+func TestParseImageURL_AutoFormat(t *testing.T) {
+	t.Parallel()
+
+	got, err := ParseImageURL("/v1/image/example.com/photo.jpg/200x200.auto")
+	if err != nil {
+		t.Fatalf("ParseImageURL() error = %v", err)
+	}
+
+	if got.Format != FormatAuto {
+		t.Errorf("Format = %q, want %q", got.Format, FormatAuto)
+	}
+}
+
 func TestParseImageURL_Errors(t *testing.T) {
 	t.Parallel()
 

internal/loadtestorigin/loadtestorigin.go

@@ -0,0 +1,87 @@
+// Package loadtestorigin is the upstream host script/loadtest points pixad
+// at, run by cmd/loadtest-origin. It answers every request, whatever its path,
+// with the same generated JPEG, so each new path is a new source image for
+// pixad to fetch, and it logs one line per request, so its log counts pixad's
+// fetches.
+package loadtestorigin
+
+import (
+	"bytes"
+	"image"
+	"image/color"
+	"image/jpeg"
+	"log/slog"
+	"math"
+	"net/http"
+	"os"
+	"time"
+)
+
+const (
+	listenAddress     = ":80"
+	readHeaderTimeout = 10 * time.Second
+	imageWidth        = 1600
+	imageHeight       = 1200
+	jpegQuality       = 85
+)
+
+// Run makes the image and serves it on port 80 until the server fails, then
+// exits the process with status 1.
+func Run() {
+	photo, err := makeJPEG()
+	if err != nil {
+		slog.Error("cannot make the image", "error", err)
+		os.Exit(1)
+	}
+
+	server := &http.Server{
+		Addr:              listenAddress,
+		Handler:           newHandler(photo),
+		ReadHeaderTimeout: readHeaderTimeout,
+	}
+
+	err = server.ListenAndServe()
+	slog.Error("server stopped", "error", err)
+	os.Exit(1)
+}
+
+// newHandler answers every request with photo and logs the request's path.
+func newHandler(photo []byte) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		slog.Info("request", "path", r.URL.Path)
+		w.Header().Set("Content-Type", "image/jpeg")
+		_, _ = w.Write(photo)
+	})
+}
+
+// makeJPEG draws colour gradients crossed with a fine pattern, so the image
+// has detail to decode and does not compress to almost nothing.
+func makeJPEG() ([]byte, error) {
+	img := image.NewRGBA(image.Rect(0, 0, imageWidth, imageHeight))
+
+	// red and green count up from 0 to 255 and wrap around, along each row
+	// and down the image.
+	var green uint8
+
+	for y := range imageHeight {
+		var red uint8
+
+		for x := range imageWidth {
+			img.SetRGBA(x, y, color.RGBA{
+				R: red, G: green, B: red ^ green, A: math.MaxUint8,
+			})
+			red++
+		}
+
+		green++
+	}
+
+	var buf bytes.Buffer
+
+	err := jpeg.Encode(&buf, img, &jpeg.Options{Quality: jpegQuality})
+	if err != nil {
+		return nil, err
+	}
+
+	return buf.Bytes(), nil
+}

internal/loadtestorigin/loadtestorigin_internal_test.go

@@ -0,0 +1,51 @@
+package loadtestorigin
+
+import (
+	"bytes"
+	"image/jpeg"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+// TestEveryPathServesTheSameJPEG checks that the origin answers any path with
+// 200 and the same JPEG, so every new path script/loadtest asks pixad for is
+// a valid source image.
+func TestEveryPathServesTheSameJPEG(t *testing.T) {
+	t.Parallel()
+
+	photo, err := makeJPEG()
+	if err != nil {
+		t.Fatalf("makeJPEG: %v", err)
+	}
+
+	size, err := jpeg.DecodeConfig(bytes.NewReader(photo))
+	if err != nil {
+		t.Fatalf("the image does not decode as a JPEG: %v", err)
+	}
+
+	if size.Width != imageWidth || size.Height != imageHeight {
+		t.Errorf("the image is %dx%d, want %dx%d",
+			size.Width, size.Height, imageWidth, imageHeight)
+	}
+
+	handler := newHandler(photo)
+
+	for _, path := range []string{"/", "/miss/1.jpg", "/herd/2.jpg"} {
+		rec := httptest.NewRecorder()
+		handler.ServeHTTP(rec, httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, path, nil))
+
+		if rec.Code != http.StatusOK {
+			t.Errorf("%s: status = %d, want %d", path, rec.Code, http.StatusOK)
+		}
+
+		if ct := rec.Header().Get("Content-Type"); ct != "image/jpeg" {
+			t.Errorf("%s: Content-Type = %q, want image/jpeg", path, ct)
+		}
+
+		if !bytes.Equal(rec.Body.Bytes(), photo) {
+			t.Errorf("%s: the body is not the image", path)
+		}
+	}
+}

internal/server/format_auto_internal_test.go

@@ -0,0 +1,46 @@
+package server
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"slices"
+	"testing"
+)
+
+// TestFormatAutoVaryNextToOrigin requests an image URL with the format auto
+// through the server's routes and verifies that the answer carries
+// Vary: Accept next to the Vary: Origin the CORS middleware sends.
+func TestFormatAutoVaryNextToOrigin(t *testing.T) {
+	t.Parallel()
+
+	source := encodeTestPNG(t, 64, 48)
+
+	upstream := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, _ *http.Request) {
+			w.Header().Set("Content-Type", "image/png")
+			_, _ = w.Write(source)
+		}))
+	t.Cleanup(upstream.Close)
+
+	s, _, _ := startImageProxy(t, upstream)
+
+	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet,
+		"/v1/image/"+upstreamHost+"/photo.png/32x24.auto", nil)
+	req.Header.Set("Origin", "https://app.example.com")
+	req.Header.Set("Accept", "image/webp")
+
+	rec := httptest.NewRecorder()
+	s.ServeHTTP(rec, req)
+
+	vary := rec.Header().Values("Vary")
+	t.Logf("status %d, Content-Type %s, Vary %v",
+		rec.Code, rec.Header().Get("Content-Type"), vary)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusOK)
+	}
+
+	if want := []string{"Origin", "Accept"}; !slices.Equal(vary, want) {
+		t.Errorf("Vary = %v, want %v", vary, want)
+	}
+}

internal/server/image_proxy_internal_test.go

@@ -0,0 +1,302 @@
+package server
+
+import (
+	"bytes"
+	"context"
+	"crypto/sha256"
+	"database/sql"
+	"encoding/hex"
+	"image"
+	"image/color"
+	"image/jpeg"
+	"image/png"
+	"io"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"sync/atomic"
+	"testing"
+
+	"go.uber.org/fx"
+	"go.uber.org/fx/fxtest"
+
+	"sneak.berlin/go/pixa/internal/config"
+	"sneak.berlin/go/pixa/internal/database"
+	"sneak.berlin/go/pixa/internal/globals"
+	"sneak.berlin/go/pixa/internal/handlers"
+	"sneak.berlin/go/pixa/internal/healthcheck"
+	"sneak.berlin/go/pixa/internal/httpfetcher"
+	"sneak.berlin/go/pixa/internal/logger"
+	"sneak.berlin/go/pixa/internal/middleware"
+)
+
+// upstreamHost is the upstream host of the image URLs below. It is a
+// documentation address (RFC 5737), which the fetcher's URL check accepts as
+// public; the fetcher's dial function connects it to the test upstream server.
+const upstreamHost = "192.0.2.10"
+
+// TestImageProxyFlow requests images through pixa's router, handlers,
+// upstream fetcher, image processor, disk cache and database, with only the
+// upstream origin replaced by a local test server. The first request for a URL
+// is fetched and converted; the second is served from the cache without
+// another upstream request. The source and the converted image are then on
+// disk, with their rows in the database.
+func TestImageProxyFlow(t *testing.T) {
+	t.Parallel()
+
+	source := encodeTestPNG(t, 64, 48)
+
+	tests := []struct {
+		name          string
+		sizeFormat    string // the <size>.<format> part of the image URL
+		contentType   string
+		decodeConfig  func(io.Reader) (image.Config, error)
+		width, height int
+	}{
+		{"resize and convert to JPEG", "32x24.jpeg", "image/jpeg",
+			jpeg.DecodeConfig, 32, 24},
+		{"orig", "orig.orig", "image/png", png.DecodeConfig, 64, 48},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			var upstreamRequests atomic.Int32
+
+			upstream := httptest.NewServer(http.HandlerFunc(
+				func(w http.ResponseWriter, _ *http.Request) {
+					upstreamRequests.Add(1)
+					w.Header().Set("Content-Type", "image/png")
+					_, _ = w.Write(source)
+				}))
+			t.Cleanup(upstream.Close)
+
+			s, db, stateDir := startImageProxy(t, upstream)
+			target := "/v1/image/" + upstreamHost + "/photo.png/" + tt.sizeFormat
+
+			first := getImage(t, s, target)
+
+			if got := first.Header().Get("X-Pixa-Cache"); got != "MISS" {
+				t.Errorf("first X-Pixa-Cache = %q, want MISS", got)
+			}
+
+			if got := first.Header().Get("Content-Type"); got != tt.contentType {
+				t.Errorf("Content-Type = %q, want %q", got, tt.contentType)
+			}
+
+			decoded, err := tt.decodeConfig(bytes.NewReader(first.Body.Bytes()))
+			if err != nil {
+				t.Fatalf("decoding the image: %v", err)
+			}
+
+			if decoded.Width != tt.width || decoded.Height != tt.height {
+				t.Errorf("image is %dx%d, want %dx%d",
+					decoded.Width, decoded.Height, tt.width, tt.height)
+			}
+
+			second := getImage(t, s, target)
+
+			if got := second.Header().Get("X-Pixa-Cache"); got != "HIT" {
+				t.Errorf("second X-Pixa-Cache = %q, want HIT", got)
+			}
+
+			if !bytes.Equal(second.Body.Bytes(), first.Body.Bytes()) {
+				t.Error("the second response is not the image the first served")
+			}
+
+			if got := upstreamRequests.Load(); got != 1 {
+				t.Errorf("upstream received %d requests, want 1", got)
+			}
+
+			checkSourceCached(t, db, stateDir, source)
+			checkVariantCached(t, db, stateDir, first.Body.Bytes(), tt.contentType)
+		})
+	}
+}
+
+// startImageProxy starts the components pixad's fx app builds, from a config
+// with a fresh state directory and upstreamHost on the allowlist, and with an
+// upstream fetcher that connects every upstream address to upstream. It
+// returns the server with its routes, the database and the state directory.
+func startImageProxy(
+	t *testing.T, upstream *httptest.Server,
+) (*Server, *sql.DB, string) {
+	t.Helper()
+
+	stateDir := t.TempDir()
+	cfg := &config.Config{
+		SigningKey:     testSigningKey,
+		StateDir:       stateDir,
+		DBURL:          "file:" + filepath.Join(stateDir, "state.sqlite3"),
+		AllowlistHosts: []string{upstreamHost},
+		// The test upstream server has no TLS.
+		AllowHTTP: true,
+		// A limit of its own, so the cache does not size itself from the
+		// host's free disk space.
+		CacheMaxBytes:           64 << 20,
+		CacheMaxBytesExplicit:   true,
+		UpstreamMaxResponseSize: config.DefaultUpstreamMaxResponseSize,
+		DownstreamTimeout:       config.DefaultDownstreamTimeout,
+	}
+
+	fetcherCfg := httpfetcher.DefaultConfig()
+	fetcherCfg.AllowHTTP = true
+	fetcherCfg.DialContext = func(
+		ctx context.Context, network, _ string,
+	) (net.Conn, error) {
+		var dialer net.Dialer
+
+		return dialer.DialContext(ctx, network, upstream.Listener.Addr().String())
+	}
+	fetcher := httpfetcher.New(fetcherCfg)
+
+	var (
+		h  *handlers.Handlers
+		mw *middleware.Middleware
+		db *database.Database
+	)
+
+	app := fxtest.New(t,
+		fx.Supply(cfg),
+		fx.Provide(
+			globals.New,
+			logger.New,
+			database.New,
+			healthcheck.New,
+			handlers.New,
+			middleware.New,
+			func() httpfetcher.Fetcher { return fetcher },
+		),
+		fx.Populate(&h, &mw, &db),
+	)
+	app.RequireStart()
+	t.Cleanup(app.RequireStop)
+
+	// Requests go straight to the router, as in newTestServer; the server's
+	// own start hook, which listens on a port, is left out.
+	s := &Server{config: cfg, mw: mw, h: h}
+	s.SetupRoutes()
+
+	return s, db.DB(), stateDir
+}
+
+// getImage sends a GET for target to s and fails unless it answers 200.
+func getImage(t *testing.T, s *Server, target string) *httptest.ResponseRecorder {
+	t.Helper()
+
+	rec := httptest.NewRecorder()
+	s.ServeHTTP(rec, httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, target, nil))
+	t.Logf("GET %s: %d, X-Pixa-Cache %s",
+		target, rec.Code, rec.Header().Get("X-Pixa-Cache"))
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("GET %s status = %d, want %d; body %s",
+			target, rec.Code, http.StatusOK, rec.Body.String())
+	}
+
+	return rec
+}
+
+// checkSourceCached checks that source is stored under its SHA-256 in
+// cache/sources, recorded in source_content, and that the source URL's row in
+// source_metadata points at it.
+func checkSourceCached(t *testing.T, db *sql.DB, stateDir string, source []byte) {
+	t.Helper()
+
+	sum := sha256.Sum256(source)
+	hash := hex.EncodeToString(sum[:])
+
+	checkFile(t, filepath.Join(stateDir, "cache", "sources", hash[0:2], hash[2:4], hash),
+		source)
+
+	var rows int
+
+	err := db.QueryRowContext(t.Context(),
+		"SELECT COUNT(*) FROM source_content WHERE content_hash = ?", hash,
+	).Scan(&rows)
+	if err != nil || rows != 1 {
+		t.Errorf("source_content rows for the source = %d (error %v), want 1",
+			rows, err)
+	}
+
+	var metadataHash string
+
+	err = db.QueryRowContext(t.Context(),
+		`SELECT content_hash FROM source_metadata
+			WHERE source_host = ? AND source_path = ?`,
+		upstreamHost, "/photo.png",
+	).Scan(&metadataHash)
+	if err != nil || metadataHash != hash {
+		t.Errorf("source_metadata content_hash = %q (error %v), want %q",
+			metadataHash, err, hash)
+	}
+}
+
+// checkVariantCached checks that the converted image served is recorded in
+// variant_content with contentType, and stored under its cache key in
+// cache/variants.
+func checkVariantCached(
+	t *testing.T, db *sql.DB, stateDir string, served []byte, contentType string,
+) {
+	t.Helper()
+
+	var cacheKey, storedType string
+
+	err := db.QueryRowContext(t.Context(),
+		"SELECT cache_key, content_type FROM variant_content",
+	).Scan(&cacheKey, &storedType)
+	if err != nil {
+		t.Fatalf("variant_content row: %v", err)
+	}
+
+	if storedType != contentType {
+		t.Errorf("variant_content content_type = %q, want %q",
+			storedType, contentType)
+	}
+
+	checkFile(t, filepath.Join(stateDir, "cache", "variants",
+		cacheKey[0:2], cacheKey[2:4], cacheKey), served)
+}
+
+// checkFile checks that the file at path holds want.
+func checkFile(t *testing.T, path string, want []byte) {
+	t.Helper()
+
+	//nolint:gosec // G304: a path under the test's state directory
+	got, err := os.ReadFile(path)
+	if err != nil {
+		t.Errorf("reading %s: %v", path, err)
+
+		return
+	}
+
+	if !bytes.Equal(got, want) {
+		t.Errorf("%s holds %d bytes that are not the %d expected",
+			path, len(got), len(want))
+	}
+}
+
+// encodeTestPNG returns an opaque width x height PNG of one color.
+func encodeTestPNG(t *testing.T, width, height int) []byte {
+	t.Helper()
+
+	img := image.NewRGBA(image.Rect(0, 0, width, height))
+	for y := range height {
+		for x := range width {
+			img.Set(x, y, color.RGBA{R: 200, G: 40, B: 40, A: 255})
+		}
+	}
+
+	var buf bytes.Buffer
+
+	err := png.Encode(&buf, img)
+	if err != nil {
+		t.Fatalf("encoding the test PNG: %v", err)
+	}
+
+	return buf.Bytes()
+}

internal/templates/generator.html

@@ -95,6 +95,7 @@
                     </label>
                     <select id="format" name="format">
                         <option value="orig" {{if eq .FormFormat "orig"}}selected{{end}}>Original</option>
+                        <option value="auto" {{if eq .FormFormat "auto"}}selected{{end}}>Auto (AVIF, WebP or JPEG)</option>
                         <option value="jpeg" {{if eq .FormFormat "jpeg"}}selected{{end}}>JPEG</option>
                         <option value="png" {{if eq .FormFormat "png"}}selected{{end}}>PNG</option>
                         <option value="webp" {{if eq .FormFormat "webp"}}selected{{end}}>WebP</option>

package.json

@@ -0,0 +1,6 @@
+{
+  "license": "GPL-3.0",
+  "devDependencies": {
+    "prettier": "3.8.1"
+  }
+}

script/bootstrap

@@ -3,16 +3,33 @@
 # this repo. Idempotent: every install is guarded by a check so already
 # installed tools are skipped. Base tooling comes from nix, apt, brew,
 # or apk (detected in that order); assumes NOTHING is present (not git,
-# make, or go). The linter is never installed on the host: golangci-lint
-# runs only inside a container, Dockerfile.lint or the Dockerfile lint
-# stage (see script/lint). A C compiler and the CGO image libraries
-# (pkg-config, vips, libheif) are installed for the govips bindings.
-# Both Dockerfiles run this script too, so their build dependencies are
-# the ones listed here.
+# make, or go). Node is used directly if installed; otherwise it is
+# installed at a pinned version via nvm (installing nvm itself first,
+# from a hash-verified release archive, never curl | sh). The linter is
+# never installed on the host: golangci-lint runs only in the lint phase
+# of the Dockerfile (see script/lint).
+#
+#   script/bootstrap         git, make, Go, and Node, Yarn and the
+#                            prettier in yarn.lock for script/fmt and
+#                            script/fmt-check: all the host needs, as
+#                            the checks compile pixa in Docker
+#   script/bootstrap --cgo   git, make, Go, and a C compiler and the
+#                            CGO image libraries (pkg-config, vips,
+#                            libheif) for the govips bindings instead
+#                            of Node: to compile pixa, in the
+#                            Dockerfile's test phase and build stage,
+#                            which format nothing
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# Pinned versions, 2026-07-06
+NODE_VERSION="22.17.0"
+NVM_VERSION="0.40.3"
+# sha256 of https://github.com/nvm-sh/nvm/archive/refs/tags/v0.40.3.tar.gz
+NVM_SHA256="5f4d6aaa04a177dc93c985e31dbc411ab6b8c6e1e21d8015dbc1372625fcd1d0"
+YARN_VERSION="1.22.22"
+
 PKGMGR=""
 SUDO=""
 
@@ -35,6 +52,10 @@ detect_pkgmgr() {
         if [ "$(id -u)" != "0" ]; then
             SUDO="sudo"
         fi
+        # This runs before the first install only. A fresh image, such
+        # as a CI runner's, has no package lists, and apt-get install
+        # finds no package without them.
+        $SUDO apt-get update
     fi
 }
 
@@ -53,6 +74,69 @@ missing() {
     ! command -v "$1" >/dev/null 2>&1
 }
 
+# verify_sha256 <file> <expected-hash>
+verify_sha256() {
+    if command -v sha256sum >/dev/null 2>&1; then
+        actual="$(sha256sum "$1" | cut -d' ' -f1)"
+    else
+        actual="$(shasum -a 256 "$1" | cut -d' ' -f1)"
+    fi
+    if [ "$actual" != "$2" ]; then
+        echo "bootstrap: sha256 mismatch for $1" >&2
+        echo "  expected: $2" >&2
+        echo "  actual:   $actual" >&2
+        exit 1
+    fi
+}
+
+# nvm is a bash script; run a command in a bash with nvm loaded
+nvm_sh() {
+    bash -c ". \"\$HOME/.nvm/nvm.sh\" && $*"
+}
+
+ensure_nvm() {
+    [ -s "$HOME/.nvm/nvm.sh" ] && return 0
+    # nvm prerequisites; nvm itself requires bash
+    if missing bash; then pkg_install bash bash bash bash; fi
+    if missing curl; then pkg_install curl curl curl curl; fi
+    if missing git; then pkg_install git git git git; fi
+    tmp="$(mktemp -d)"
+    curl -fsSL -o "$tmp/nvm.tar.gz" \
+        "https://github.com/nvm-sh/nvm/archive/refs/tags/v${NVM_VERSION}.tar.gz"
+    verify_sha256 "$tmp/nvm.tar.gz" "$NVM_SHA256"
+    mkdir -p "$HOME/.nvm"
+    tar -xzf "$tmp/nvm.tar.gz" -C "$HOME/.nvm" --strip-components=1
+    rm -rf "$tmp"
+}
+
+ensure_node() {
+    if ! missing node; then return 0; fi
+    ensure_nvm
+    nvm_sh "nvm install $NODE_VERSION"
+}
+
+ensure_yarn() {
+    if ! missing yarn; then return 0; fi
+    if ! missing corepack; then
+        corepack enable
+        corepack prepare "yarn@$YARN_VERSION" --activate
+    elif [ -s "$HOME/.nvm/nvm.sh" ]; then
+        nvm_sh "nvm use $NODE_VERSION >/dev/null && corepack enable && \
+            corepack prepare yarn@$YARN_VERSION --activate"
+    else
+        npm install -g "yarn@$YARN_VERSION"
+    fi
+}
+
+install_js_deps() {
+    if missing yarn && [ -s "$HOME/.nvm/nvm.sh" ]; then
+        nvm_sh "nvm use $NODE_VERSION >/dev/null && cd \"$ROOT\" && \
+            yarn install --frozen-lockfile"
+    else
+        yarn install --frozen-lockfile
+    fi
+}
+
 # CGO dependencies for govips (image processing)
 ensure_cgo_deps() {
     # cgo compiles with gcc on Linux; build-base and build-essential
@@ -71,7 +155,16 @@ ensure_cgo_deps() {
     fi
 }
 
+usage() {
+    echo "usage: script/bootstrap [--cgo]" >&2
+    exit 2
+}
+
 main() {
+    case "$*" in
+        "" | --cgo) ;;
+        *) usage ;;
+    esac
     cd "$ROOT"
 
     # Base tooling
@@ -81,8 +174,15 @@ main() {
     # Go toolchain
     if missing go; then pkg_install go golang go go; fi
 
-    # CGO image libraries
+    # CGO image libraries where pixa is compiled; elsewhere Node, Yarn
+    # and prettier
+    if [ "$*" = "--cgo" ]; then
         ensure_cgo_deps
+    else
+        ensure_node
+        ensure_yarn
+        install_js_deps
+    fi
 
     go mod download
 

script/check

@@ -1,7 +1,8 @@
 #!/bin/sh
 # script/check: run all checks (test, lint, fmt-check). Our own
-# extension to scripts-to-rule-them-all. Must not modify any files.
-# Generic: usually needs no adaptation.
+# extension to scripts-to-rule-them-all. test and lint are Docker
+# phases; fmt-check is native, because a formatter writes the working
+# tree. Must not modify any files.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"

script/cibuild

@@ -1,18 +1,29 @@
 #!/bin/sh
-# script/cibuild: run the CI build. The Dockerfile runs the checks
-# (make fmt-check, lint, test) as build steps. This script passes a new
-# CHECK_EPOCH on every run, so Docker runs those steps instead of
-# reusing cached results: a successful run means the checks ran and
-# passed on this tree. Generic: needs no adaptation. The Gitea workflow
-# runs this on push.
+# script/cibuild: run the CI build. It bootstraps first: a CI runner
+# checks out and runs this and nothing else, and script/fmt-check runs
+# the formatter on the host, which a pristine checkout cannot do.
+# --no-cache for the same reason as script/docker: the gate phases the
+# final stage depends on are RUN steps, and a cached one is a check that
+# did not run.
 set -eu
 
-ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    epoch="$(date +%s)$$"
-    docker build --build-arg CHECK_EPOCH="$epoch" .
+    "$SCRIPT_DIR/bootstrap"
+    "$SCRIPT_DIR/check"
+    # Own line: a failing command substitution inside an argument does
+    # not trip `set -e`, so the inline form degrades silently to an
+    # empty constant. VERSION is computed here because .dockerignore
+    # excludes .git, so `git describe` in a build stage yields an empty
+    # version without failing.
+    version="$(git describe --tags --always --dirty 2>/dev/null || true)"
+    [ -n "$version" ] || version="unknown"
+    docker build --no-cache \
+        --build-arg VERSION="$version" \
+        -t "$("$SCRIPT_DIR/projectname")" .
 }
 
 main "$@"

script/docker

@@ -1,9 +1,8 @@
 #!/bin/sh
 # script/docker: build the Docker image tagged with the project name.
-# Identical in all repos; the tag comes from script/projectname. Like
-# script/cibuild, it passes a new CHECK_EPOCH, so the build runs the
-# checks instead of reusing cached results. Generic: needs no
-# adaptation.
+# Identical in all repos; the tag comes from script/projectname.
+# --no-cache because the gate phases the final stage depends on are RUN
+# steps, and a cached one is a check that did not run.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
@@ -11,8 +10,15 @@ ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    epoch="$(date +%s)$$"
-    docker build --build-arg CHECK_EPOCH="$epoch" \
+    # Own line: a failing command substitution inside an argument does
+    # not trip `set -e`, so the inline form degrades silently to an
+    # empty constant. VERSION is computed here because .dockerignore
+    # excludes .git, so `git describe` in a build stage yields an empty
+    # version without failing.
+    version="$(git describe --tags --always --dirty 2>/dev/null || true)"
+    [ -n "$version" ] || version="unknown"
+    docker build --no-cache \
+        --build-arg VERSION="$version" \
         -t "$("$SCRIPT_DIR/projectname")" .
 }
 

script/fmt

@@ -4,11 +4,31 @@ set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# Must match the pin in script/bootstrap.
+NODE_VERSION="22.17.0"
+
+# script/bootstrap installs node and yarn under nvm and leaves neither
+# on the PATH of the shell that called it, so resolve the pinned
+# toolchain here the way bootstrap's own install step does. nvm is a
+# bash script, hence the subshell.
+run_yarn() {
+    if command -v yarn >/dev/null 2>&1; then
+        exec yarn "$@"
+    fi
+    if [ ! -s "$HOME/.nvm/nvm.sh" ]; then
+        echo "fmt: no yarn; run script/bootstrap first" >&2
+        exit 1
+    fi
+    exec bash -c '. "$HOME/.nvm/nvm.sh" && nvm use "$1" >/dev/null &&
+        shift && exec yarn "$@"' bash "$NODE_VERSION" "$@"
+}
+
 main() {
     cd "$ROOT"
     echo "Formatting code..."
     # shellcheck disable=SC2046 # word splitting of file list is wanted
     gofmt -w $(find . -name '*.go' -not -path './vendor/*')
+    run_yarn run prettier --write '**/*.md' --tab-width 4 --prose-wrap always
 }
 
 main "$@"

script/fmt-check

@@ -5,6 +5,25 @@ set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# Must match the pin in script/bootstrap.
+NODE_VERSION="22.17.0"
+
+# script/bootstrap installs node and yarn under nvm and leaves neither
+# on the PATH of the shell that called it, so resolve the pinned
+# toolchain here the way bootstrap's own install step does. nvm is a
+# bash script, hence the subshell.
+run_yarn() {
+    if command -v yarn >/dev/null 2>&1; then
+        exec yarn "$@"
+    fi
+    if [ ! -s "$HOME/.nvm/nvm.sh" ]; then
+        echo "fmt-check: no yarn; run script/bootstrap first" >&2
+        exit 1
+    fi
+    exec bash -c '. "$HOME/.nvm/nvm.sh" && nvm use "$1" >/dev/null &&
+        shift && exec yarn "$@"' bash "$NODE_VERSION" "$@"
+}
+
 main() {
     cd "$ROOT"
     echo "Checking formatting..."
@@ -13,6 +32,7 @@ main() {
         gofmt -l . | grep -v '^vendor/'
         exit 1
     fi
+    run_yarn run prettier --check '**/*.md' --tab-width 4 --prose-wrap always
 }
 
 main "$@"

script/install-precommit

@@ -1,13 +1,13 @@
 #!/bin/sh
 # script/install-precommit: install the git pre-commit hook that runs
 # script/precommit. Our own extension to scripts-to-rule-them-all.
-# Generic: needs no adaptation.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
+    hook=".git/hooks/pre-commit"
     printf '#!/bin/sh\nset -e\nscript/precommit\n' > .git/hooks/pre-commit
     chmod +x .git/hooks/pre-commit
     echo "pre-commit hook installed: runs script/precommit"

script/lint

@@ -1,37 +1,23 @@
 #!/bin/sh
-# script/lint: run golangci-lint over the whole tree. This is the only
-# way the linter is run, everywhere; it is never installed on the host.
+# script/lint: run the linter. Linting is a phase of the Dockerfile and
+# this builds that phase alone; the linter is never installed or run on
+# a developer host, where a shared result cache and a host-global lock
+# make its answer untrustworthy.
 #
-# Inside a container it runs the linter. Anywhere else it builds
-# Dockerfile.lint, whose last step runs this script again inside that
-# container.
-#
-# Dockerfile.lint and the Dockerfile lint stage set container=docker
-# (the systemd convention for marking a container) to say where we are.
-# /.dockerenv cannot: it is missing inside build steps, and present on
-# hosts that are themselves containers.
+# The phase is not the last stage in the file, so it is built only when
+# --target names it. --no-cache because a cached lint layer is a lint
+# that did not run. The tag makes each build replace the previous image
+# instead of leaving a dangling one behind.
 set -eu
 
-ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    if [ "${container:-}" = docker ]; then
-        # `golangci-lint config verify` is not run: it fetches its JSON
-        # schema over an unpinned live HTTPS call, which REPO_POLICIES.md
-        # forbids.
-        echo "Running linter..."
-        golangci-lint run --config .golangci.yml ./...
-    else
-        # A new CACHEBUST on every run means the lint step is never
-        # served from cache (see Dockerfile.lint). The cacheonly output
-        # leaves no image behind.
-        docker build \
-            --progress=plain \
-            --build-arg CACHEBUST="$(date +%s)-$$" \
-            --output=type=cacheonly \
-            -f Dockerfile.lint .
-    fi
+    docker build --no-cache \
+        --target lint \
+        -t "$("$SCRIPT_DIR/projectname")-lint" .
 }
 
 main "$@"

script/loadtest

@@ -0,0 +1,177 @@
+#!/bin/sh
+# script/loadtest: measure pixad's throughput, latency and peak memory.
+#
+#   script/loadtest [duration [clients]]    (defaults: 10s and 4)
+#
+# A benchmark, not a check: script/check does not run it. It needs Docker
+# and Go. It builds the image with script/docker and builds vegeta, the
+# load tool, from a pinned commit. Each scenario then gets a new pixad
+# container and a new origin container (cmd/loadtest-origin, which answers
+# every path with the same JPEG), and vegeta sends requests for <duration>
+# from <clients> clients at once, each asking for an image resized to
+# 400x300 WebP:
+#
+#   hit   the same image every time, put in the cache first
+#   miss  a new source image every time
+#   herd  each new source image once per client in a row, so that all
+#         clients ask for it at the same time
+#
+# For each, it prints vegeta's report, pixad's peak resident memory and
+# how many requests reached the origin. README.md says how to read them.
+set -eu
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
+
+# vegeta v12.13.0, 2026-10-04
+VEGETA_COMMIT=4b240c3089fa4aa10816542d64a74294d974211f
+
+# pixad refuses upstream hosts with private or local addresses, so the
+# containers share a network in 203.0.113.0/24, a range set aside for
+# documentation (RFC 5737) that pixad does not refuse and that is never
+# routed on the internet.
+SUBNET=203.0.113.0/24
+
+usage() {
+    echo "usage: script/loadtest [duration [clients]]" >&2
+    exit 2
+}
+
+main() {
+    duration="${1:-10s}"
+    clients="${2:-4}"
+    # The duration is a whole number, not zero (vegeta takes 0 to mean no
+    # end), followed by ms, s, m or h.
+    case "$duration" in
+        *ms) number="${duration%ms}" ;;
+        *s | *m | *h) number="${duration%?}" ;;
+        *) usage ;;
+    esac
+    case "$number" in
+        "" | *[!0-9]*) usage ;;
+    esac
+    [ "$number" -gt 0 ] || usage
+    # The number of clients is a whole number that does not start with 0,
+    # which also refuses zero: vegeta reads a leading 0 as octal.
+    case "$clients" in
+        *[!0-9]* | 0*) usage ;;
+    esac
+
+    cd "$ROOT"
+    run="pixa-loadtest-$$"
+    tmp="$(mktemp -d)"
+    trap cleanup EXIT
+    trap 'exit 1' HUP INT TERM
+
+    "$SCRIPT_DIR/docker"
+    # The image's ID, so a build elsewhere that moves the tag does not
+    # change what a later scenario starts.
+    image="$(docker image inspect --format '{{.Id}}' \
+        "$("$SCRIPT_DIR/projectname")")"
+
+    GOBIN="$tmp" go install "github.com/tsenart/vegeta/v12@$VEGETA_COMMIT"
+    # The origin runs in a container, so it is built for the Docker host.
+    CGO_ENABLED=0 GOOS=linux \
+        GOARCH="$(docker version --format '{{.Server.Arch}}')" \
+        go build -o "$tmp/loadtest-origin" ./cmd/loadtest-origin
+
+    docker network create --subnet "$SUBNET" "$run" >/dev/null
+
+    start_containers
+    # Put the image the hit scenario asks for in the cache.
+    docker exec "$run-pixad" wget -q -O /dev/null \
+        "http://localhost:8080/v1/image/origin/hit.jpg/400x300.webp"
+    attack hit hit_targets
+    stop_containers
+
+    start_containers
+    attack miss miss_targets
+    stop_containers
+
+    start_containers
+    attack herd herd_targets
+    stop_containers
+}
+
+# start_containers starts a new origin and a new pixad, and waits up to 30
+# seconds for pixad's health check to pass.
+start_containers() {
+    docker run -d --name "$run-origin" \
+        --network "$run" --network-alias origin \
+        -v "$tmp/loadtest-origin:/usr/local/bin/loadtest-origin:ro" \
+        --entrypoint /usr/local/bin/loadtest-origin "$image" >/dev/null
+    docker run -d --name "$run-pixad" \
+        --network "$run" -p 127.0.0.1::8080 --health-interval=1s \
+        -e PIXA_SIGNING_KEY="$(head -c 32 /dev/urandom | base64)" \
+        -e PIXA_ALLOWLIST_HOSTS=origin -e PIXA_ALLOW_HTTP=true \
+        "$image" >/dev/null
+
+    waited=0
+    until [ "$(docker inspect --format '{{.State.Health.Status}}' \
+        "$run-pixad")" = healthy ]; do
+        if [ "$waited" -ge 30 ]; then
+            echo "loadtest: pixad not healthy after 30 seconds; its log:" >&2
+            docker logs "$run-pixad" >&2
+            exit 1
+        fi
+        sleep 1
+        waited=$((waited + 1))
+    done
+    pixa="http://$(docker port "$run-pixad" 8080/tcp)"
+}
+
+stop_containers() {
+    docker rm -f "$run-pixad" "$run-origin" >/dev/null
+}
+
+# attack <scenario> <targets>: send the requests <targets> prints and
+# report on them.
+attack() {
+    echo
+    echo "== $1: $clients clients for $duration"
+    "$2" | "$tmp/vegeta" attack -lazy -rate 0 -workers "$clients" \
+        -max-workers "$clients" -duration "$duration" -max-body 0 |
+        "$tmp/vegeta" report
+    # pixad is process 1 in its container: the entrypoint execs it.
+    echo "pixad peak memory (VmHWM):" \
+        "$(docker exec "$run-pixad" awk '/^VmHWM:/ { print $2, $3 }' \
+            /proc/1/status)"
+    echo "requests to the origin:" \
+        "$(docker logs "$run-origin" 2>&1 | grep -c ' request ')"
+}
+
+# The targets functions print vegeta targets until vegeta stops reading.
+
+hit_targets() {
+    while :; do
+        echo "GET $pixa/v1/image/origin/hit.jpg/400x300.webp"
+    done
+}
+
+miss_targets() {
+    i=0
+    while :; do
+        i=$((i + 1))
+        echo "GET $pixa/v1/image/origin/miss/$i.jpg/400x300.webp"
+    done
+}
+
+herd_targets() {
+    i=0
+    while :; do
+        i=$((i + 1))
+        n=0
+        while [ "$n" -lt "$clients" ]; do
+            n=$((n + 1))
+            echo "GET $pixa/v1/image/origin/herd/$i.jpg/400x300.webp"
+        done
+    done
+}
+
+cleanup() {
+    docker rm -f "$run-pixad" "$run-origin" >/dev/null 2>&1 || :
+    docker network rm "$run" >/dev/null 2>&1 || :
+    rm -rf "$tmp"
+}
+
+main "$@"

script/setup

@@ -1,7 +1,6 @@
 #!/bin/sh
 # script/setup: set up the repo for development after a fresh clone:
-# installs dependencies (script/bootstrap) and the git pre-commit hook.
-# Add any repo-specific initialization (db init, .env template) here.
+# installs dependencies and the git pre-commit hook.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"

script/test

@@ -1,27 +1,19 @@
 #!/bin/sh
-# script/test: run the test suite. CGO dependencies (pkg-config, vips,
-# libheif) come from nix-shell when not already available (e.g. inside
-# a Docker build or an existing nix-shell).
+# script/test: run the test suite. Testing is a phase of the Dockerfile
+# and this builds that phase alone, on the same terms as script/lint:
+# --target because a phase that is not the last stage is built only when
+# named, --no-cache because a cached test layer is a test that did not
+# run, and a tag so each build replaces the previous image.
 set -eu
 
-ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
-
-run_with_cgo_deps() {
-    if command -v pkg-config >/dev/null 2>&1; then
-        sh -c "$1"
-    else
-        nix-shell -p pkg-config vips libheif git --run "$1"
-    fi
-}
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    echo "Running tests..."
-    # Run without -v first for clean output on success; on failure rerun
-    # with -v for full diagnostics, then exit non-zero (REPO_POLICIES.md
-    # conditional-verbose-rerun pattern). The first run already proved the
-    # tests broken, so the build fails even if the rerun happens to pass.
-    run_with_cgo_deps "CGO_ENABLED=1 go test -timeout 30s -race -cover ./... || { echo '--- Rerunning with -v for details ---'; CGO_ENABLED=1 go test -timeout 30s -race -v ./...; exit 1; }"
+    docker build --no-cache \
+        --target test \
+        -t "$("$SCRIPT_DIR/projectname")-test" .
 }
 
 main "$@"

yarn.lock

@@ -0,0 +1,8 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+
+prettier@3.8.1:
+  version "3.8.1"
+  resolved "https://registry.yarnpkg.com/prettier/-/prettier-3.8.1.tgz#edf48977cf991558f4fcbd8a3ba6015ba2a3a173"
+  integrity sha512-UOnG6LftzbdaHZcKoPFtOcCKztrQ57WkHDeRD9t/PTQtmT0NHSeWWepj6pS0z/N7+08BHFDQVUrfmfMRcZwbMg==