Stamp Docker image version from the host; flush profiles on error exit (closes #75)

Docker images reported commit unknown because the build ran git inside the container while .dockerignore excludes .git, and VERSION was never overridden. script/docker and script/cibuild now compute version, commit and date on the host and pass them as build args; the Dockerfile runs no git and falls back to dev and unknown, never empty, on a bare docker build.

Profiling a failing command gave a truncated or missing profile: Entry and each command goroutine called os.Exit(1), skipping the deferred profile writers in main. Entry now returns a status that main exits with after its defers run, and command goroutines report failure through one RunOperation helper, which also restores PID-lock release and graceful shutdown on failure.

model: claude-opus-4-8 (implementation, review); claude-fable-5-1 (merge)

Co-authored-by: clawbot <clawbot@noreply.example.org>

script/cibuild

@@ -56,8 +56,23 @@ main() {
     docker build --output=type=cacheonly \
         --build-arg CHECK_EPOCH="$epoch" -f Dockerfile.lint .
 
+    # Version, commit and build date are computed here on the host, the
+    # same way script/docker does, and passed into the product build so
+    # the CI-built image reports its real source. The build context
+    # excludes .git (see .dockerignore), so the build cannot derive them
+    # itself; without these it would stamp the Dockerfile's dev/unknown
+    # fallbacks. VERSION comes from script/version, the source of truth
+    # shared with the Makefile.
+    version="$("$ROOT/script/version")"
+    commit="$(git rev-parse HEAD 2>/dev/null || echo unknown)"
+    commit_date="$(git show -s --format=%cs HEAD 2>/dev/null || echo unknown)"
+
     epoch="$(date +%s%N)$$"
-    docker build --build-arg CHECK_EPOCH="$epoch" .
+    docker build --build-arg CHECK_EPOCH="$epoch" \
+        --build-arg VERSION="$version" \
+        --build-arg COMMIT="$commit" \
+        --build-arg COMMIT_DATE="$commit_date" \
+        .
 }
 
 main "$@"