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

script/docker and script/cibuild compute the version (via script/version),
commit and build date on the host and pass them as build args; the
Dockerfile no longer runs git, which always returned "unknown" because
the build context excludes .git. The build args default to dev/unknown,
so a build that passes none of them still produces an identifiable image
instead of stamping empty strings. A dirty tree is reflected through
script/version's -dirty suffix.

main now exits via os.Exit(run()), so its deferred CPU/heap profile
writers flush before the process ends, and Entry returns a status code
instead of calling os.Exit. Each command ran its operation in an fx
goroutine that called os.Exit(1) on failure, discarding those profiles
and the PID-lock release; they now route the error to the return path
through one RunOperation helper. errReported keeps Entry from printing an
already-reported failure twice.

model: claude-opus-4-8

script/docker

@@ -24,7 +24,24 @@ main() {
     # whether the tree is clean. The Dockerfile now refuses to build
     # without a non-empty value, so this is required, not optional.
     epoch="$(date +%s%N)$$"
+
+    # Version, commit and build date are computed here on the host,
+    # where .git exists, and passed into the build. The build context
+    # excludes .git (see .dockerignore), so the container cannot derive
+    # them itself -- it used to try and always got "unknown", giving
+    # every image a "commit: unknown" it could not be traced from.
+    # VERSION comes from script/version, the source of truth shared with
+    # the Makefile, so a Docker build reports the same string (tag,
+    # dev-<sha>, or a -dirty variant) that a local build of the same
+    # tree would.
+    version="$("$SCRIPT_DIR/version")"
+    commit="$(git rev-parse HEAD 2>/dev/null || echo unknown)"
+    commit_date="$(git show -s --format=%cs HEAD 2>/dev/null || echo unknown)"
+
     docker build --build-arg CHECK_EPOCH="$epoch" \
+        --build-arg VERSION="$version" \
+        --build-arg COMMIT="$commit" \
+        --build-arg COMMIT_DATE="$commit_date" \
         -t "$("$SCRIPT_DIR/projectname")" .
 }