README.md

@@ -116,10 +116,14 @@ alpine. We provide:
   `script/bootstrap`, then `script/install-precommit`
 - `script/projectname` — output the project name (our own extension); used by
   `script/docker` for the image tag
-- `script/test` — `docker build --no-cache --target test -t prompts-test .`,
+- `script/test` —
-  building the `test` phase of the `Dockerfile` (no tests defined here)
+  `docker build --no-cache --target test --output type=cacheonly .`, building
-- `script/lint` — `docker build --no-cache --target lint -t prompts-lint .`,
+  the `test` phase of the `Dockerfile` without writing an image (no tests
-  building the `lint` phase, which runs prettier over the markdown files
+  defined here)
+- `script/lint` —
+  `docker build --no-cache --target lint --output type=cacheonly .`, building
+  the `lint` phase, which runs prettier over the markdown files, without writing
+  an image
 - `script/fmt` — format all markdown files with prettier (writes; native, not in
   a container)
 - `script/fmt-check` — check formatting (read-only; native)

TODO.md

@@ -21,6 +21,14 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-10-07: `script/lint` and `script/test` now build with
+  `--output type=cacheonly` in place of a tag (issue 123), so they still run
+  their phase uncached and fail on a failing step but write no image. Nothing
+  used those images, and writing one out cost about 16 seconds of a Go
+  repository's test build. `script/cibuild` and `script/docker` keep their tags.
+  `REPO_POLICIES.md`, both checklists and the README no longer say the gate
+  builds are tagged. Not yet tried on the shared runner. Repositories pick this
+  up on their next re-vendor.
 - 2026-10-07: The canonical `.gitea/workflows/check.yml` now sets
   `timeout-minutes: 20` on its `check` job (issue 120), so a hung build frees
   the shared runner instead of holding it until the runner's own limit.

prompts/EXISTING_REPO_CHECKLIST.md

@@ -132,16 +132,19 @@ with your task.
       `script/install-precommit`, shimmed by `make hooks`) runs it
 - [ ] README has an **Entrypoints** section documenting the `script/`
       entrypoints and linking the standard
-- [ ] `script/lint` and `script/test` build their phase by name
+- [ ] `script/lint` and `script/test` each run
-      (`docker build --no-cache --target <phase> -t <name>-<phase> .`), and no
+      `docker build --no-cache --target <phase> --output type=cacheonly .`,
-      host invocation anywhere in the repo can produce a lint verdict — grep for
+      which builds their phase by name and writes no image, and no host
-      the linter's own name across `script/`, the `Makefile` and CI config, not
+      invocation anywhere in the repo can produce a lint verdict — grep for the
-      just `script/lint`. A second path is likeliest here: a `make lint-fast`,
+      linter's own name across `script/`, the `Makefile` and CI config, not just
-      an older host-versus-container branch, or a CI step calling the binary
+      `script/lint`. A second path is likeliest here: a `make lint-fast`, an
+      older host-versus-container branch, or a CI step calling the binary
       directly. `script/fmt` and `script/fmt-check` are expected hits and stay
       on the host.
-- [ ] Every `docker build` in `script/` is tagged — an untagged one leaves a
+- [ ] No `docker build` in `script/` leaves a dangling image behind:
-      dangling image behind on every run, on every host and CI runner
+      `script/lint` and `script/test` write no image, and `script/docker` and
+      `script/cibuild` tag theirs. A build that writes an untagged image leaves
+      one behind on every run, on every host and CI runner.
 - [ ] `script/cibuild` runs `script/bootstrap` before `script/check`, and builds
       the image with `--no-cache`. Without the bootstrap the CI run dies in
       `script/fmt-check`, which runs the formatter on the host and finds nothing

prompts/NEW_REPO_CHECKLIST.md

@@ -143,11 +143,14 @@ are thin shims calling them. Model scripts:
       it
 - [ ] `script/setup` / `make setup` — readies a fresh clone: runs `bootstrap`,
       then `install-precommit`, plus repo-specific init
-- [ ] `script/test` / `make test` — `docker build --no-cache --target test .`,
+- [ ] `script/test` / `make test` —
-      tagged; the phase runs real tests, not a no-op (90-second timeout,
+      `docker build --no-cache --target test --output type=cacheonly .`, which
-      60-second hard cap on wall time)
+      writes no image; the phase runs real tests, not a no-op (90-second
-- [ ] `script/lint` / `make lint` — `docker build --no-cache --target lint .`,
+      timeout, 60-second hard cap on wall time)
-      tagged. No lint verdict may come from a host invocation of the linter.
+- [ ] `script/lint` / `make lint` —
+      `docker build --no-cache --target lint --output type=cacheonly .`, which
+      writes no image. No lint verdict may come from a host invocation of the
+      linter.
 - [ ] `script/fmt` / `make fmt` — formats code (writes; native, never in a
       container)
 - [ ] `script/fmt-check` / `make fmt-check` — checks formatting (read-only;
@@ -169,8 +172,9 @@ are thin shims calling them. Model scripts:
       `script/bootstrap` leaves the node and yarn it installs off the `PATH` of
       the shell that called it, so a bare `yarn` exits 127 on a runner carrying
       nothing but docker and git.
-- [ ] Every `docker build` in `script/` is tagged, so no invocation leaves a
+- [ ] No `docker build` in `script/` leaves a dangling image behind:
-      dangling image behind
+      `script/lint` and `script/test` write no image, and `script/docker` and
+      `script/cibuild` tag theirs
 - [ ] `script/precommit` — called by the pre-commit hook; runs `script/check`
 - [ ] `script/install-precommit` — installs the pre-commit hook that runs
       `script/precommit`

prompts/REPO_POLICIES.md

@@ -118,9 +118,8 @@ style conventions are in separate documents:
   and nothing else:
 
     ```sh
-    tag="$(script/projectname)"
+    docker build --no-cache --target lint --output type=cacheonly .
-    docker build --no-cache --target lint -t "$tag-lint" .
+    docker build --no-cache --target test --output type=cacheonly .
-    docker build --no-cache --target test -t "$tag-test" .
     ```
 
     **A stage that is not the last one in the file is built only when the final
@@ -130,12 +129,15 @@ style conventions are in separate documents:
     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
+    **The gate builds write no image.** With `--output type=cacheonly` the phase
-    `script/cibuild` and `script/docker`. An untagged build leaves a dangling
+    runs and a failing step fails the build, but the result is not exported.
-    image behind on every invocation, on every developer host and every CI
+    Nothing uses those images, and writing one out is slow: a Go test phase's
-    runner; a tagged one replaces the previous image. Each script assigns the
+    image holds the toolchain and every compiled package. A build given neither
-    tag on its own line before the build, so `set -e` stops it where
+    `--output` nor `-t` writes an untagged image and leaves it dangling, on
-    `script/projectname` fails.
+    every developer host and every CI runner. `script/cibuild` and
+    `script/docker` build the image that ships and tag it, so each build
+    replaces the previous image; each assigns the tag on its own line before the
+    build, so `set -e` stops it where `script/projectname` fails.
 
     Inside a phase the tool is invoked directly — `golangci-lint`, `go test`,
     `eslint`, `prettier` — never through `make lint` or `script/test`, which are

script/lint

@@ -6,8 +6,8 @@
 #
 # 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
+# that did not run. --output type=cacheonly writes no image, since
-# instead of leaving a dangling one behind.
+# nothing uses one.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
@@ -15,13 +15,9 @@ ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    # The tag gets its own line: a failing command substitution inside
-    # an argument does not trip `set -e`, so the inline form degrades
-    # silently to an empty constant.
-    tag="$("$SCRIPT_DIR/projectname")"
     docker build --no-cache \
         --target lint \
-        -t "$tag-lint" .
+        --output type=cacheonly .
 }
 
 main "$@"

script/test

@@ -2,8 +2,8 @@
 # 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
+# named, and --no-cache because a cached test layer is a test that did
-# run, and a tag so each build replaces the previous image.
+# not run. --output type=cacheonly writes no image, since nothing uses one.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
@@ -11,13 +11,9 @@ ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    # The tag gets its own line: a failing command substitution inside
-    # an argument does not trip `set -e`, so the inline form degrades
-    # silently to an empty constant.
-    tag="$("$SCRIPT_DIR/projectname")"
     docker build --no-cache \
         --target test \
-        -t "$tag-test" .
+        --output type=cacheonly .
 }
 
 main "$@"