Run golangci-lint only in docker, on every run (closes #55)

script/lint builds the new Dockerfile.lint, where golangci-lint runs as
a build step. The lint stage is rebuilt on every run, so an unchanged
tree is linted too; the module download stays cached. script/bootstrap
no longer installs golangci-lint. The Dockerfile lint stage calls
golangci-lint directly, since make lint now starts a docker build.
golangci-lint config verify is not run: it fetches its schema live over
unpinned HTTPS.

Model: opus-5-5

Dockerfile

@@ -9,7 +9,8 @@ RUN go mod download
 COPY . .
 
 RUN make fmt-check
-RUN make lint
+# Not make lint: script/lint is a docker build, which cannot run in here.
+RUN golangci-lint run --config .golangci.yml ./...
 
 # Build stage — tests and compilation
 # golang 1.24.13-alpine (2026-03-10)

Dockerfile.lint

@@ -0,0 +1,19 @@
+# Lint image, built by script/lint: golangci-lint runs as a build step, so a
+# successful build is a clean lint. Works where the docker daemon is remote
+# and bind mounts are impossible.
+
+# golangci/golangci-lint:v2.12.2 (Debian-based), 2026-08-07
+FROM golangci/golangci-lint:v2.12.2@sha256:5cceeef04e53efe1470638d4b4b4f5ceefd574955ab3941b2d9a68a8c9ad5240 AS deps
+
+WORKDIR /src
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+# script/lint rebuilds this stage on every run, by this name; the module
+# download above stays cached.
+FROM deps AS lint
+
+COPY . .
+
+RUN golangci-lint run --config .golangci.yml ./...

README.md

@@ -496,15 +496,18 @@ standard: normalized scripts in `script/` are the entrypoints for the
 development workflow, and the Makefile targets are thin shims that call
 them. We provide:
 
-- `script/bootstrap` — install all dependencies (Go, golangci-lint, Go
-  module download), idempotently
+- `script/bootstrap` — install all dependencies (Go, Go module
+  download), idempotently; golangci-lint is not installed, it runs in
+  docker
 - `script/setup` — make a fresh clone ready for development: runs
   `script/bootstrap`, then `script/install-precommit`
 - `script/projectname` — output the project name (`secret`); used by
   other scripts such as `script/docker`
 - `script/test` — run `go vet` and the test suite (verbose rerun on
   failure)
-- `script/lint` — run `golangci-lint`
+- `script/lint` — run `golangci-lint` in docker only: builds
+  `Dockerfile.lint`, where the linter is a build step that runs on every
+  call, also on an unchanged tree
 - `script/fmt` — format all Go code (writes)
 - `script/fmt-check` — check formatting without writing
 - `script/check` — run `script/test`, `script/lint`, and

TODO.md

@@ -25,6 +25,13 @@ Bring the repo into policy compliance in one commit:
 
 # Completed Steps
 
+- 2026-10-04: Lint runs only in docker: `script/lint` builds
+  `Dockerfile.lint`, where golangci-lint is a build step rebuilt on
+  every run (`--no-cache-filter`), so an unchanged tree is linted too;
+  the module download stays cached. `script/bootstrap` no longer
+  installs golangci-lint, and the `Dockerfile` lint stage calls it
+  directly instead of `make lint`. `golangci-lint config verify` is not
+  run: it fetches its schema live over unpinned HTTPS.
 - 2026-10-04: A PGP unlocker whose metadata has no usable GPG key ID
   no longer panics: `GetID()` warns with the unlocker's directory and
   returns `pgp-unknown`. `ListUnlockers` skips, with a warning, an

script/bootstrap

@@ -6,6 +6,7 @@
 # make, node, yarn, go, or python). Node is used directly if installed;
 # otherwise a pinned version is installed via nvm (installing nvm
 # itself first, from a hash-verified release archive, never curl | sh).
+# golangci-lint is never installed: script/lint runs it in docker.
 #
 # Uncomment the language sections in main() that apply to this repo.
 set -eu
@@ -136,12 +137,6 @@ main() {
 
     # ---- Go repos ----
     if missing go; then pkg_install go golang go go; fi
-    # golangci-lint: packaged in nix, brew, and apk. On apt there is no
-    # package: download a specific release archive from GitHub and
-    # verify its hash (verify_sha256), never curl | sh.
-    if missing golangci-lint; then
-        pkg_install golangci-lint golangci-lint golangci-lint golangci-lint
-    fi
     go mod download
 
     # ---- Python repos ----

script/lint

@@ -1,14 +1,24 @@
 #!/bin/sh
-# script/lint: run the linter.
+# script/lint: run the linter, in docker only. Builds Dockerfile.lint,
+# where golangci-lint runs as a build step.
+#
+# A cached build lints nothing, so --no-cache-filter rebuilds the lint
+# stage on every run, an unchanged tree included. It ignores a stage name
+# that does not exist, so --target names the same stage: a rename then
+# fails the build instead of serving the lint from cache. cacheonly keeps
+# no image; only the build's success matters.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    # CGO is required (Makefile exports this too)
-    export CGO_ENABLED=1
-    golangci-lint run --timeout 5m
+    docker build \
+        --progress=plain \
+        --target lint \
+        --no-cache-filter=lint \
+        --output=type=cacheonly \
+        -f Dockerfile.lint .
 }
 
 main "$@"