Run the checks again on every script/cibuild (closes #54)

On an unchanged tree docker served every check step of the Dockerfile
from its build cache, so a second script/cibuild ran no lint, tests or
build and still succeeded.

script/cibuild now passes the current time as the CHECK_EPOCH build
argument. The lint and build stages each declare it after their module
download and before `COPY . .`. A build argument whose value changes
makes every RUN step after its declaration miss the cache, so the
checks run on each build while the base images, the apk install and the
module downloads stay cached.

Model: opus-5-5

Dockerfile

@@ -6,6 +6,11 @@ WORKDIR /src
 COPY go.mod go.sum ./
 RUN go mod download
 
+# script/cibuild sets CHECK_EPOCH to the current time, so the RUN steps
+# below run again on each build, an unchanged tree included, while the
+# steps above stay cached. ARG is per stage: the build stage declares it too.
+ARG CHECK_EPOCH
+
 COPY . .
 
 RUN make fmt-check
@@ -25,6 +30,9 @@ WORKDIR /build
 COPY go.mod go.sum ./
 RUN go mod download
 
+# As in the lint stage: the RUN steps below run again on each script/cibuild.
+ARG CHECK_EPOCH
+
 COPY . .
 
 RUN make test

README.md

@@ -523,7 +523,8 @@ them. We provide:
 - `script/docker` — build the Docker image tagged with the project name
 - `script/cibuild` — CI entrypoint: `docker build --ulimit
   memlock=-1:-1 .` (memguard needs mlock; the Dockerfile runs the
-  checks)
+  checks), with a new `CHECK_EPOCH` build argument on every run so the
+  checks run again on an unchanged tree
 - `script/precommit` — pre-commit checks: `go mod tidy` verification,
   then `script/check`
 - `script/install-precommit` — install the git pre-commit hook that

TODO.md

@@ -25,6 +25,14 @@ Bring the repo into policy compliance in one commit:
 
 # Completed Steps
 
+- 2026-10-04: `script/cibuild` runs the checks again on an unchanged
+  tree (https://git.eeqj.de/sneak/secret/issues/54). It passes the
+  current time as the `CHECK_EPOCH` build argument, which both the lint
+  and the build stage of the `Dockerfile` declare after their module
+  download, so the `RUN` steps below the argument run again on each
+  build while the base images and module downloads stay cached. Before,
+  a second run on the same tree took every check from the build cache
+  and reported success having run nothing.
 - 2026-10-04: A failed unlocker add no longer leaves a partial unlocker
   directory (https://git.eeqj.de/sneak/secret/issues/48).
   `secret unlocker add pgp` resolves the GPG key's fingerprint once, for

script/cibuild

@@ -4,13 +4,17 @@
 # The Gitea workflow runs this on push. The memlock ulimit lets the tests
 # that lock large secrets in memory (memguard mlocks them) run; under the
 # lower limit of a plain `docker build .` they are skipped.
+# A cached build checks nothing: a new CHECK_EPOCH on every run makes the
+# Dockerfile's check steps run again on an unchanged tree, while its base
+# images and module downloads stay cached.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    docker build --ulimit memlock=-1:-1 .
+    docker build --ulimit memlock=-1:-1 \
+        --build-arg CHECK_EPOCH="$(date +%s)" .
 }
 
 main "$@"