Run every lint-class check inside Docker (closes #38)

Add a root Dockerfile.lint that carries the checks as build steps -- a
`lint` stage running `hugo --minify --printPathWarnings` and a
`fmt-check` stage running the prettier check -- and reduce script/lint
and script/fmt-check to building their stage. A successful build is a
clean check. There is no host path and deliberately no "am I already
inside a container?" branch, which would be a host lint path in
disguise.

The two stages share a `base` whose first four instructions are
byte-identical to the main Dockerfile's, so the expensive
`RUN script/bootstrap` layer that compiles the pinned Hugo from source
is a cache hit against the main image instead of a second build of the
same thing.

Resolve the resulting recursion by splitting the checks by where they
run, not with an escape hatch. `make check` runs script/lint, so the
main Dockerfile can no longer `RUN make check`: that would be
docker-in-docker inside a bare Alpine with no docker client and no
daemon socket, and script/cibuild is what CI runs on every push. The
main Dockerfile therefore runs `make test`, the production build, and
script/cibuild builds it and then calls script/lint and
script/fmt-check. CI still covers the production build, lint and the
format check, and it runs exactly what a developer runs.

script/fmt stays on the host because it rewrites the working tree,
which a container build cannot do. That makes it the authoritative
copy of the prettier version, scope and flags that the fmt-check stage
duplicates; both sides carry a keep-in-sync note. The duplication is
forced: any `RUN script/fmt-check` inside the image is the recursion
again.

Caching is waived for the checks in the shape this repo already
settled: `ARG CHECK_EPOCH` with no default, declared and guarded
separately in each stage because ARG does not cross a FROM, with the
value expanded into the checked command as well as the guard so
invalidation does not rest on BuildKit's treatment of an unreferenced
ARG. All four image-building entrypoints now generate and pass it --
script/cibuild, script/docker, script/lint, script/fmt-check.

Verified: two consecutive script/lint runs on an unchanged tree both
executed hugo for real, with script/bootstrap CACHED; a constant-epoch
counterfactual restored the false green (exit 0, lint layer CACHED, no
hugo output); an empty epoch failed closed on the guard; a broken
template failed the lint stage and an unformatted README failed the
fmt-check stage, both reverted and re-run clean; script/cibuild and
`make check` are green with all three checks demonstrably executing.

Dockerfile

@@ -1,8 +1,18 @@
-# Hugo static-site build image. The build runs `make check` (a clean
-# `hugo --minify` production build, the `--printPathWarnings` lint
-# build, then the read-only prettier docs check), so the image build
-# fails on any formatting or Hugo build error. This is what CI
-# (script/cibuild) runs on every push.
+# Hugo static-site build image. The build runs `make test` -- a clean
+# `hugo --minify` production build -- so the image build fails on any
+# template, content or config error.
+#
+# It deliberately does NOT run `make check`. `make check` runs
+# script/lint, and script/lint is a `docker build` of Dockerfile.lint,
+# so `RUN make check` here would be docker-in-docker inside a bare
+# alpine with no docker client and no daemon socket. The checks are
+# therefore split by where they run: the production build here, lint and
+# the prettier format check in Dockerfile.lint. Do not reintroduce a
+# `make check` (or a `make lint` / `make fmt-check`) line in this file.
+#
+# CI coverage is unaffected: script/cibuild builds this image and then
+# calls script/lint and script/fmt-check, so every check in `make check`
+# still runs on every push -- see script/cibuild.
 #
 # Build this only via script/cibuild or script/docker: both pass the
 # CHECK_EPOCH build argument that this file requires, and a bare
@@ -41,5 +51,5 @@ COPY . .
 ARG CHECK_EPOCH
 RUN [ -n "$CHECK_EPOCH" ] || exit 1
 
-# Run all checks - build fails if any check fails.
-RUN echo "check epoch: ${CHECK_EPOCH}" && make check
+# Run the production build - build fails if the site does not build.
+RUN echo "check epoch: ${CHECK_EPOCH}" && make test

Dockerfile.lint

@@ -0,0 +1,85 @@
+# Lint image. Every lint-class check for this repo runs here and
+# nowhere else: the checks are build steps, so a successful build IS a
+# clean lint. There is no host lint path and no "am I already in a
+# container?" bypass -- script/lint and script/fmt-check are reduced to
+# building the stage below that carries their check.
+#
+# Build this only via script/lint or script/fmt-check: both pass the
+# CHECK_EPOCH build argument that the stages here require, and a bare
+# `docker build -f Dockerfile.lint .` fails by design. See the guards.
+#
+# Why this is a separate file from the main Dockerfile, and why that
+# one no longer runs `make check`: `make check` runs script/lint, and
+# script/lint is now a `docker build`. A `RUN make check` in an image
+# would therefore be docker-in-docker inside a bare alpine with no
+# docker client and no daemon socket. The checks are split by where
+# they run instead -- the main Dockerfile runs the production build,
+# this file runs lint and the format check -- so no image ever shells
+# back into `make check`. script/cibuild drives all of them, so CI
+# coverage is unchanged.
+
+# alpine 3.21, 2026-02-28
+FROM alpine@sha256:c3f8e73fdb79deaebaa2037150150191b9dcbfba68b4a46d70103204c53f4709 AS base
+
+WORKDIR /src
+
+# Keep these four instructions byte-identical to the main Dockerfile's,
+# in the same order: Docker keys layers on the instruction chain, not on
+# the file they live in, so an identical prefix means this stage is a
+# cache hit against the main image's layers. script/bootstrap compiles
+# the pinned Hugo from source, which is by far the most expensive step
+# here, and it must not be paid twice.
+COPY script/ script/
+RUN script/bootstrap
+
+COPY . .
+
+# --- lint -------------------------------------------------------------
+#
+# The site's lint is a clean build that surfaces broken internal links
+# and template path problems: `hugo` fails on build errors and
+# --printPathWarnings reports render-target collisions.
+#
+# The flags are inlined rather than reached through `RUN script/lint`,
+# and that is forced, not lazy: script/lint is the docker build that
+# produces this stage, so calling it here is the recursion described
+# above. Keep these flags in sync with script/lint's documentation.
+FROM base AS lint
+
+# CHECK_EPOCH is a per-invocation nonce supplied by script/lint. Without
+# it an unchanged tree serves the check layer from cache: the lint never
+# executes and the build still exits 0, which is precisely the false
+# green this repo already fixed once in the main Dockerfile. Caching is
+# explicitly waived for lint, so the value is expanded into the checked
+# command as well as the guard -- two independent value-keyed
+# invalidation points, so a cache miss never depends on BuildKit's
+# treatment of an unreferenced ARG. Declared with no default: a default
+# is a constant, and a constant is a stable cache key. ARG is
+# stage-scoped, so the fmt-check stage below declares its own.
+#
+# Everything above this line still caches, so script/bootstrap is not
+# rebuilt.
+ARG CHECK_EPOCH
+RUN [ -n "$CHECK_EPOCH" ] || exit 1
+RUN echo "lint epoch: ${CHECK_EPOCH}" && hugo --minify --printPathWarnings
+
+# --- fmt-check --------------------------------------------------------
+#
+# The read-only prettier check over this repo's markdown and CSS. Same
+# version, same scope and same flags as script/fmt, which is the
+# authoritative copy and stays on the host because it writes to the
+# working tree; keep the two in sync. The exclusions live in
+# .prettierignore with the reason for each.
+#
+# Built as a sibling of `lint` rather than stacked on top of it so that
+# a --target build runs exactly one check, and so a lint failure and a
+# formatting failure are reported independently.
+FROM base AS fmt-check
+
+# Same nonce, same reasoning as the lint stage above. Declared again
+# because ARG does not cross a FROM.
+ARG CHECK_EPOCH
+RUN [ -n "$CHECK_EPOCH" ] || exit 1
+RUN echo "fmt-check epoch: ${CHECK_EPOCH}" && \
+    npx --yes "prettier@3.4.2" --check \
+    '**/*.md' '**/*.css' --tab-width 4 --prose-wrap always

README.md

@@ -39,8 +39,12 @@ build, and the formatting check:
 make check
 ```
 
+The lint build and the formatting check run inside Docker, so `make check` needs
+a working Docker daemon; there is no host fallback.
+
 `make fmt` rewrites the repo's markdown and CSS to the project's prettier
-settings; run it if `make check` fails on formatting.
+settings; run it if `make check` fails on formatting. It runs on the host,
+because it writes to your working tree.
 
 To contribute to this site, contact **sneak@sneak.berlin** for git repository
 access.
@@ -61,22 +65,41 @@ provide:
   git pre-commit hook
 - `script/test` — the correctness check: a clean `hugo --minify` production
   build
-- `script/lint` — a clean build that surfaces broken links and path collisions
+- `script/lint` — a clean build that surfaces broken links and path collisions,
+  run inside Docker: it builds the `lint` stage of `Dockerfile.lint`, where the
+  check is a build step, so a successful build is a clean lint
 - `script/fmt` — format every markdown and CSS file in the repo with prettier;
-  the exclusions live in `.prettierignore` with the reason for each
-- `script/fmt-check` — check that formatting (read-only)
+  the exclusions live in `.prettierignore` with the reason for each. The one
+  prettier entrypoint that runs on the host, because it writes to your working
+  tree
+- `script/fmt-check` — check that formatting (read-only), also inside Docker:
+  the `fmt-check` stage of `Dockerfile.lint`
 - `script/check` — run `script/test`, `script/lint`, then `script/fmt-check`;
   modifies no tracked files
 - `script/docker` — build the Docker image tagged with the project name
-- `script/cibuild` — the CI build; the Dockerfile runs `make check`
+- `script/cibuild` — the CI build: the main image (the production build), then
+  `script/lint` and `script/fmt-check`
 - `script/install-precommit` — install the git pre-commit hook that runs
   `script/check`
 
-Build the image through `script/cibuild` or `script/docker` only. Both pass a
-per-invocation `CHECK_EPOCH` build argument that the Dockerfile requires, so the
-`make check` layer can never be served from cache — without it Docker returns a
-green it did not earn. A bare `docker build .` fails closed on the Dockerfile's
-`CHECK_EPOCH` guard rather than caching its way to a false success.
+Every lint run for this repo happens inside a container. `script/lint` and
+`script/fmt-check` have no host path and no "already inside a container?"
+branch, so what a developer runs and what CI runs are the same build.
+
+That is also why the main `Dockerfile` runs `make test` rather than
+`make check`: `make check` calls `script/lint`, which is itself a
+`docker build`, so a `make check` inside an image would be docker-in-docker in a
+bare Alpine with no docker client and no daemon socket. The checks are split by
+where they run — the production build in `Dockerfile`, lint and the format check
+in `Dockerfile.lint` — and `script/cibuild` drives all three, so CI coverage is
+unchanged.
+
+Build any image through `script/cibuild`, `script/docker`, `script/lint` or
+`script/fmt-check` only. All four pass a per-invocation `CHECK_EPOCH` build
+argument that the Dockerfiles require, so a check layer can never be served from
+cache — without it Docker returns a green it did not earn. A bare `docker build`
+fails closed on the `CHECK_EPOCH` guard rather than caching its way to a false
+success.
 
 A convenience `make serve` target runs `hugo server` for local preview.
 

TODO.md

@@ -20,17 +20,64 @@ wrangler CLI install, an exact version), and the Hugo that builds the published
 site is a deliberate pinned version rather than whatever the base image's
 package repo serves. The site now ships a Cloudflare Pages `_headers` file, so
 its response security headers are declared in the repo instead of being whatever
-the edge defaults to — unverified in production until the next deploy.
+the edge defaults to — unverified in production until the next deploy. Every
+lint-class check now runs inside a container and nowhere else: `script/lint` and
+`script/fmt-check` build stages of `Dockerfile.lint`, with no host path to fall
+back to.
 
 # Next Step
 
-Move the artifact actions in `.gitea/workflows/deploy.yml` to v4 once this Gitea
-Actions instance serves the v4 artifact protocol; they are pinned on the
-deprecated v3 line because v4 fails here (#20). This touches the live deploy
-path, so it needs a real workflow run to verify rather than a local check.
+Add the missing `cibuild` and `precommit` shims to the `Makefile`, so that every
+documented entrypoint has a make target and the documented "always use make
+targets" rule is actually satisfiable
+(https://git.eeqj.de/sneak/lora.vegas/issues/34). Done when `make cibuild` and
+`make precommit` exist, are declared `.PHONY`, and the README Entrypoints
+section matches.
 
 # Completed Steps
 
+- 2026-08-10: moved every lint-class check into Docker
+  (https://git.eeqj.de/sneak/lora.vegas/issues/38). A new root `Dockerfile.lint`
+  carries the checks as build steps — a `lint` stage running
+  `hugo --minify --printPathWarnings` and a `fmt-check` stage running the
+  prettier check — on a shared `base` stage whose first four instructions are
+  byte-identical to the main `Dockerfile`'s, so the expensive
+  `RUN script/bootstrap` layer that compiles Hugo from source is a cache hit
+  against the main image rather than a second build of the same thing.
+  `script/lint` and `script/fmt-check` are now nothing but a `docker build` of
+  their stage; there is no host path and deliberately no "already inside a
+  container?" branch, which would be a host lint path in disguise. The recursion
+  this creates was resolved by splitting the checks by where they run rather
+  than by adding an escape hatch: `make check` runs `script/lint`, so the main
+  `Dockerfile` can no longer `RUN make check` — that would be docker-in-docker
+  inside a bare Alpine with no docker client and no daemon socket, and
+  `script/cibuild` is what CI runs on every push. The main `Dockerfile`
+  therefore runs `make test`, the production build, and `script/cibuild` builds
+  it and then calls `script/lint` and `script/fmt-check`, so CI still covers all
+  three and cannot drift from what a developer runs. `script/fmt` stays on the
+  host because it rewrites the working tree, which makes it the authoritative
+  copy of the prettier version and flags that the `fmt-check` stage duplicates;
+  both sides carry a keep-in-sync note, and that duplication is forced, since
+  any `RUN script/fmt-check` inside the image is the recursion again. Caching is
+  waived for the checks exactly as the main `Dockerfile` already does it:
+  `ARG CHECK_EPOCH` with no default, declared and guarded separately in each
+  stage because `ARG` does not cross a `FROM`, with the value expanded into the
+  checked command as well as the guard. All four image-building entrypoints now
+  generate and pass it — `script/cibuild`, `script/docker`, `script/lint`,
+  `script/fmt-check` — which is the failure mode this repo already hit once, a
+  Dockerfile guard asserting a property one entrypoint did not supply. Verified
+  rather than assumed: two consecutive `script/lint` runs on an unchanged tree
+  both executed hugo for real (second run 2.9s wall, `RUN script/bootstrap`
+  `CACHED`, distinct epoch echoed, `Total in 37 ms` printed), a constant-epoch
+  counterfactual restored the false green (exit 0 in 0.25s, lint layer `CACHED`,
+  no hugo output at all), an empty epoch failed closed on the guard, a broken
+  template failed the lint stage with hugo's own render error, and an over-long
+  line appended to `README.md` failed the fmt-check stage with
+  `[warn] README.md`; both violations were reverted and re-run clean. Not
+  changed here, and still true: the lint stage fails on hugo build errors but
+  not on render-target collisions, which `--printPathWarnings` only prints
+  (https://git.eeqj.de/sneak/lora.vegas/issues/25) — containerising the run
+  neither fixes nor worsens that
 - 2026-08-10: added the `LICENSE` file and made the README say what it says
   (closes #10). The repo is public (`private: false` on the Gitea API, verified
   rather than assumed), so the owner's standing policy — MIT on any public repo
@@ -226,8 +273,40 @@ path, so it needs a real workflow run to verify rather than a local check.
 
 # Future Steps
 
+Startable work first. Everything under "Blocked" waits on somebody or something
+outside this repo, so nothing there may be picked up as the Next Step.
+
+- Make the prettier scope's exclusion of dot-directories explicit instead of
+  leaning on `.gitignore` (https://git.eeqj.de/sneak/lora.vegas/issues/33)
+- Fix the README's SSH-only clone URL, and add the two entrypoints the
+  Entrypoints section omits, `script/precommit` and `script/projectname`
+  (https://git.eeqj.de/sneak/lora.vegas/issues/36)
+- Drop the Go toolchain and module cache from the check image's final layer;
+  they are needed to build hugo and dead weight afterwards
+  (https://git.eeqj.de/sneak/lora.vegas/issues/28)
+- Add a timeout guard to `script/test` and `script/lint` so a wedged build fails
+  instead of hanging (https://git.eeqj.de/sneak/lora.vegas/issues/16)
+- Sync the reformat of `REPO_POLICIES.md` back upstream to `prompts` so the
+  canonical copy is clean under the shared prettier settings and future syncs
+  are a straight byte copy
+- Keep mesh channel and signal group listings current
+
+## Blocked
+
+- Decide whether `script/lint` should fail on render-target collisions rather
+  than only print them; `--printPathWarnings` exits 0 today, so the signal is
+  reported and not enforced. Owner call, since it changes what the gate rejects
+  (https://git.eeqj.de/sneak/lora.vegas/issues/25)
+- Move the artifact actions in `.gitea/workflows/deploy.yml` to v4 once this
+  Gitea Actions instance serves the v4 artifact protocol; they are pinned on the
+  deprecated v3 line because v4 fails here
+  (https://git.eeqj.de/sneak/lora.vegas/issues/20). This touches the live deploy
+  path, so it needs a real workflow run to verify rather than a local check
 - Move the deploy container to a pinned node 22 so the wrangler pin can advance
-  past 4.86.0 (#21)
+  past 4.86.0 (https://git.eeqj.de/sneak/lora.vegas/issues/21)
+- Delete the stale remote branches `feat/initial-site` and `security-audit`;
+  only the owner can remove them
+  (https://git.eeqj.de/sneak/lora.vegas/issues/15)
 - After the next deploy, confirm the `_headers` file actually took effect, on
   both `https://lora.vegas/` and `https://www.lora.vegas/`: `curl -sSI` against
   each must show `strict-transport-security` or `content-security-policy`.
@@ -237,12 +316,10 @@ path, so it needs a real workflow run to verify rather than a local check.
   `includeSubDomains` rests on `www.lora.vegas` being served by this same Pages
   project, which was established behaviourally from identical response bodies
   rather than from the Cloudflare dashboard. If `www` turns out not to be
-  covered, the `includeSubDomains` decision has to be revisited (#14)
+  covered, the `includeSubDomains` decision has to be revisited
+  (https://git.eeqj.de/sneak/lora.vegas/issues/14)
 - Decide the HSTS `includeSubDomains` and `preload` posture for `lora.vegas`.
   Both are owner calls: neither can be walked back inside the max-age window,
-  and `includeSubDomains` binds hostnames this repo does not control (#14)
-- Sync the reformat of `REPO_POLICIES.md` back upstream to `prompts` so the
-  canonical copy is clean under the shared prettier settings and future syncs
-  are a straight byte copy
+  and `includeSubDomains` binds hostnames this repo does not control
+  (https://git.eeqj.de/sneak/lora.vegas/issues/14)
 - Verify the Cloudflare Pages deploy still works after the workflow changes
-- Keep mesh channel and signal group listings current

script/check

@@ -3,6 +3,11 @@
 # scripts-to-rule-them-all. Must not modify any tracked files. Runs the
 # canonical order: the clean production build, then the lint build that
 # reports path warnings, then the read-only formatting check.
+#
+# The last two run inside Docker (they build stages of Dockerfile.lint),
+# so this script needs a working docker daemon. That is deliberate:
+# every lint run for this repo happens in a container, and there is no
+# host fallback to drop back to.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"

script/cibuild

@@ -1,17 +1,32 @@
 #!/bin/sh
-# script/cibuild: run the CI build. The Dockerfile runs `make check`,
-# so a successful build implies all checks pass. The Gitea workflow
-# runs this on push.
+# script/cibuild: run the CI build. The Gitea workflow runs this on
+# push, and it is the single entrypoint that covers everything:
 #
-# That implication only holds because of CHECK_EPOCH. Docker keys the
-# `RUN make check` layer on content, so on an unchanged tree it is
-# served from cache: the checks never execute and the build still exits
-# 0. Passing a value that differs on every invocation invalidates that
-# layer and everything below it, while the script/bootstrap toolchain
-# layer above it keeps caching.
+#   1. the main Dockerfile, which runs the clean `hugo --minify`
+#      production build (`make test`)
+#   2. script/lint, which builds Dockerfile.lint's `lint` stage
+#   3. script/fmt-check, which builds Dockerfile.lint's `fmt-check`
+#      stage
+#
+# Steps 2 and 3 are delegated to the same scripts a developer runs, so
+# CI cannot drift from `make check`. They are separate builds rather
+# than a `RUN make check` inside the main image because script/lint is
+# itself a `docker build`: shelling back into `make check` from an image
+# would be docker-in-docker inside a bare alpine with no docker client
+# and no daemon socket. See Dockerfile.lint for the full reasoning.
+#
+# The main image build below only implies a passing production build
+# because of CHECK_EPOCH. Docker keys the `RUN make test` layer on
+# content, so on an unchanged tree it is served from cache: the build
+# never executes and the image build still exits 0. Passing a value that
+# differs on every invocation invalidates that layer and everything
+# below it, while the script/bootstrap toolchain layer above it keeps
+# caching. script/lint and script/fmt-check each do the same for their
+# own stage.
 set -eu
 
-ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
@@ -25,6 +40,9 @@ main() {
     # 0, so `$$` is appended to cover that degradation.
     epoch="$(date +%s%N)$$"
     docker build --build-arg CHECK_EPOCH="$epoch" .
+
+    "$SCRIPT_DIR/lint"
+    "$SCRIPT_DIR/fmt-check"
 }
 
 main "$@"

script/fmt

@@ -6,6 +6,12 @@
 # the reason next to each entry: the Hugo layout templates, which are
 # Go templates and not HTML, and content/, whose reformatting was
 # measured to change the rendered page.
+#
+# This runs on the host, unlike the read-only check: it rewrites the
+# working tree, which a container build cannot do. It is therefore the
+# authoritative copy of the prettier version, scope and flags -- the
+# fmt-check stage of Dockerfile.lint duplicates them and must be kept in
+# sync with this file.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"

script/fmt-check

@@ -1,17 +1,27 @@
 #!/bin/sh
 # script/fmt-check: check the formatting of this repo's markdown and
-# CSS (read-only). Same scope and same settings as script/fmt - keep
-# the two in sync - but fails instead of writing.
+# CSS (read-only). Like script/lint, it runs only in Docker: it builds
+# the `fmt-check` stage of Dockerfile.lint, where prettier runs as a
+# build step. Leaving prettier to run on the host here would have left
+# `make check` with a host lint path, which is the thing being removed.
+#
+# The version, scope and flags live in Dockerfile.lint and must stay in
+# sync with script/fmt, which is the authoritative copy and stays on the
+# host because it writes to the working tree.
+#
+# Dockerfile.lint requires the CHECK_EPOCH build argument, generated
+# here exactly as script/cibuild generates it -- see that script for why
+# the check layer must not be allowed to cache, and why the value is
+# built in an assignment rather than inline.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
-PRETTIER_VERSION="3.4.2"
-
 main() {
     cd "$ROOT"
-    npx --yes "prettier@${PRETTIER_VERSION}" --check \
-        '**/*.md' '**/*.css' --tab-width 4 --prose-wrap always
+    epoch="$(date +%s%N)$$"
+    docker build -f Dockerfile.lint --target fmt-check \
+        --build-arg CHECK_EPOCH="$epoch" .
 }
 
 main "$@"

script/lint

@@ -1,15 +1,26 @@
 #!/bin/sh
-# script/lint: this Hugo site has no dedicated linter, so the lint gate
-# is a clean build that surfaces broken internal links and template
-# path problems. It is a real check: `hugo` fails on build errors, and
-# --printPathWarnings reports render-target collisions.
+# script/lint: run the lint. This Hugo site has no dedicated linter, so
+# the lint gate is a clean build that surfaces broken internal links and
+# template path problems -- but where it runs is not negotiable: every
+# lint run happens inside a Docker container, so this script does
+# nothing except build the `lint` stage of Dockerfile.lint. The check is
+# a build step there, so a successful build is a clean lint. There is
+# deliberately no host fallback and no "already inside a container?"
+# branch: either would be a host lint path wearing a disguise.
+#
+# Dockerfile.lint requires the CHECK_EPOCH build argument, generated
+# here exactly as script/cibuild generates it -- see that script for why
+# the check layer must not be allowed to cache, and why the value is
+# built in an assignment rather than inline.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    hugo --minify --printPathWarnings
+    epoch="$(date +%s%N)$$"
+    docker build -f Dockerfile.lint --target lint \
+        --build-arg CHECK_EPOCH="$epoch" .
 }
 
 main "$@"