Enforce hard stop when bug is already fixed on main

Subagent was ignoring the "stop and report back" instruction and still
creating regression tests + PRs for bugs that no longer reproduce.

- Harness: clarify definition of "not reproducible", replace soft
  "stop and report back" with explicit HARD STOP + forbidden actions
- Skill: add CRITICAL instruction in subagent dispatch prompt so it
  sees the constraint before even reading the harness

Signed-off-by: Heng Qian <qianheng@amazon.com>

Author: qianheng-aws

.claude/commands/ppl-bugfix.md

@@ -73,7 +73,9 @@ Agent(
   prompt: "Read .claude/harness/ppl-bugfix-harness.md and follow it to fix GitHub issue #<issue_number>.
            Follow Phase 0 through Phase 3 in order.
            Phase 0.3 defines TDD execution flow. Do NOT skip any phase.
-           Post the Decision Log (Phase 3.4) before completing."
+           CRITICAL: If Phase 0.1 determines the bug is already fixed on main, HARD STOP.
+           Do NOT write tests, do NOT create a PR — just comment/close the issue and report back.
+           If the bug IS reproducible, post the Decision Log (Phase 3.4) before completing."
 )
 ```
 

.claude/harness/ppl-bugfix-harness.md

@@ -19,16 +19,16 @@ Read the issue title, description, and any reproduction steps before proceeding.
 ./gradlew :integ-test:integTest -Dtests.class="*<TestClass>" -Dtests.method="<testMethod>"
 ```
 
-**If not reproducible on latest `main`**:
+**If the bug does not reproduce on latest `main`** — meaning the test scenario runs but produces correct results instead of the reported error — the bug is already fixed. This is distinct from "can't set up the scenario" (which is an infra issue).
 
 | Finding | Action |
 |---------|--------|
-| Already fixed by another commit | Comment with fixing commit hash, close as duplicate |
-| Only on older version | Comment with version where it's fixed, close as resolved |
+| Already fixed by another commit | `gh issue comment` with fixing commit/PR, then `gh issue close` |
+| Only on older version | `gh issue comment` with version where it's fixed, then `gh issue close` |
 | Intermittent / environment-specific | Label `flaky` or `needs-info`, do NOT close |
 | Insufficient info to reproduce | Comment asking for repro steps, label `needs-info` |
 
-In all cases, **stop and report back** — do not proceed to Phase 1.
+**HARD STOP**: Do NOT proceed to Phase 1, 2, or 3. Do NOT write tests. Do NOT create a PR. Report back with the finding and the action taken (comment/close). Your job is done.
 
 ### 0.2 Classify and Route