feat: PM-Agent also need to look at PR comments

From Gitea issue #116.

Authored by the PM agent's worker; the merge gate is the approver. Refs #116.

Agent: pm-agent (issue #116, mode implement)

infra/agent/Containerfile

@@ -233,6 +233,11 @@ CMD ["/bin/bash"]
 # =============================================================================
 FROM agent-runner AS verify
 COPY probe-validation.sh /opt/verify/probe-validation.sh
+# The pull-request-mention fixtures the dispatcher selftest is driven by. COPYed into THIS
+# stage only — they are test data and have no business in the shipped image — and the
+# selftest FAILS rather than skips if it cannot find them (see pr_fixture_path()), so this
+# line going missing breaks the build instead of quietly deleting a test suite.
+COPY testdata/pr-mention-fixtures.json /opt/verify/pr-mention-fixtures.json
 RUN --network=none /bin/bash -euo pipefail <<'VERIFY'
 echo "--- no network (the build-time stand-in for run --network none) ---"
 if getent hosts registry.npmjs.org >/dev/null 2>&1 || curl -sS --max-time 3 -o /dev/null https://1.1.1.1 2>/dev/null; then
@@ -259,7 +264,8 @@ for e in pm-worker pm-dispatch; do
   grep -q "takes no arguments" <<<"$out" || { echo "UNEXPECTED: $e accepted an argument: $out"; exit 1; }
   echo "    $e: rejected"
 done
-echo "--- the dispatcher selftest (branch vocabulary, result envelopes, Job template, persona) ---"
+echo "--- the dispatcher selftest (branch vocabulary, result envelopes, Job template, persona,"
+echo "    and the pull-request mention trigger over committed Gitea-shaped fixtures) ---"
 PM_SELFTEST=1 /usr/local/bin/pm-dispatch
 echo "--- the entrypoints are root-owned and NOT writable by the runtime uid ---"
 for f in /usr/local/bin/pm-worker /usr/local/bin/pm-dispatch /etc/pm-agent/worker-job-template.yaml; do