Assign the image tag on its own line in script/ (closes #101)

script/cibuild, script/docker, script/lint and script/test passed the
tag from script/projectname inline to docker build, where a failing
command substitution does not trip set -e. Each now assigns it to `tag`
on its own line first, so the script stops where script/projectname
fails. The comment above it says why; the REPO_POLICIES.md snippets show
the same form.

Model: opus-5-5

TODO.md

@@ -21,6 +21,13 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-10-05: `script/cibuild`, `script/docker`, `script/lint` and `script/test`
+  now assign the image tag from `script/projectname` on its own line before the
+  `docker build` (issue 101), so `set -e` stops the script where
+  `script/projectname` fails instead of running `docker build` with a broken
+  tag. The comment above it in each script says why, and the snippets in
+  `REPO_POLICIES.md` show the same form. Repositories pick this up on their next
+  re-vendor.
 - 2026-10-04: Went through the fleet findings recorded on 2026-08-09 (issue 62)
   and added the two rules `REPO_POLICIES.md` did not yet state: a new or changed
   check is proven by planting a defect it must catch; and a change to a separate

prompts/REPO_POLICIES.md

@@ -118,8 +118,9 @@ style conventions are in separate documents:
   and nothing else:
 
     ```sh
-    docker build --no-cache --target lint -t "$(script/projectname)-lint" .
-    docker build --no-cache --target test -t "$(script/projectname)-test" .
+    tag="$(script/projectname)"
+    docker build --no-cache --target lint -t "$tag-lint" .
+    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
@@ -132,7 +133,9 @@ style conventions are in separate documents:
     **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.
+    runner; a tagged one replaces the previous image. Each script 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
@@ -434,13 +437,15 @@ style conventions are in separate documents:
   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.
+    # The version and the tag each get their 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"
+    tag="$(script/projectname)"
     docker build --no-cache \
         --build-arg VERSION="$version" \
-        -t "$(script/projectname)" .
+        -t "$tag" .
     ```
 
     `--always` makes an untagged repo yield an abbreviated commit hash rather

script/cibuild

@@ -14,15 +14,17 @@ main() {
     cd "$ROOT"
     "$SCRIPT_DIR/bootstrap"
     "$SCRIPT_DIR/check"
-    # Own line: a failing command substitution inside an argument does
-    # not trip `set -e`, so the inline form degrades silently to an
-    # empty constant. The VERSION build argument takes precedence over
-    # the version a build stage derives from the .git in the context.
+    # The version and the tag each get their own line: a failing
+    # command substitution inside an argument does not trip `set -e`,
+    # so the inline form degrades silently to an empty constant. The
+    # VERSION build argument takes precedence over the version a build
+    # stage derives from the .git in the context.
     version="$(git describe --tags --always --dirty 2>/dev/null || true)"
     [ -n "$version" ] || version="unknown"
+    tag="$("$SCRIPT_DIR/projectname")"
     docker build --no-cache \
         --build-arg VERSION="$version" \
-        -t "$("$SCRIPT_DIR/projectname")" .
+        -t "$tag" .
 }
 
 main "$@"

script/docker

@@ -10,15 +10,17 @@ ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    # Own line: a failing command substitution inside an argument does
-    # not trip `set -e`, so the inline form degrades silently to an
-    # empty constant. The VERSION build argument takes precedence over
-    # the version a build stage derives from the .git in the context.
+    # The version and the tag each get their own line: a failing
+    # command substitution inside an argument does not trip `set -e`,
+    # so the inline form degrades silently to an empty constant. The
+    # VERSION build argument takes precedence over the version a build
+    # stage derives from the .git in the context.
     version="$(git describe --tags --always --dirty 2>/dev/null || true)"
     [ -n "$version" ] || version="unknown"
+    tag="$("$SCRIPT_DIR/projectname")"
     docker build --no-cache \
         --build-arg VERSION="$version" \
-        -t "$("$SCRIPT_DIR/projectname")" .
+        -t "$tag" .
 }
 
 main "$@"

script/lint

@@ -15,9 +15,13 @@ ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
+    # The tag gets its own line: a failing command substitution inside
+    # an argument does not trip `set -e`, so the inline form degrades
+    # silently to an empty constant.
+    tag="$("$SCRIPT_DIR/projectname")"
     docker build --no-cache \
         --target lint \
-        -t "$("$SCRIPT_DIR/projectname")-lint" .
+        -t "$tag-lint" .
 }
 
 main "$@"

script/test

@@ -11,9 +11,13 @@ ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
+    # The tag gets its own line: a failing command substitution inside
+    # an argument does not trip `set -e`, so the inline form degrades
+    # silently to an empty constant.
+    tag="$("$SCRIPT_DIR/projectname")"
     docker build --no-cache \
         --target test \
-        -t "$("$SCRIPT_DIR/projectname")-test" .
+        -t "$tag-test" .
 }
 
 main "$@"