fix(runner): prevent Gemini CLI exit 42 on workflow add (#893)

## Summary
- Add `clear_session_ids()` to `GeminiSessionManager` to clear stale
session IDs from disk
- Call it from `mark_dirty()` when workflow changes trigger
reinitialisation
- Prevents exit code 42 crash from resuming invalid session in new CWD

## Test plan
- [x] Unit tests pass (452 passed)
- [x] Ruff lint/format clean
- [ ] Manual test: add workflow mid-Gemini session, verify no crash

Fixes: RHOAIENG-52260

🤖 Generated with [Claude Code](https://claude.com/claude-code)

**Jira:**
[RHOAIENG-52260](https://issues.redhat.com/browse/RHOAIENG-52260)

---------

Co-authored-by: Ambient Code Bot <bot@ambient-code.local>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: ambient-code[bot] <ambient-code[bot]@users.noreply.github.com>

Author: 4 people

components/runners/ambient-runner/ambient_runner/bridges/gemini_cli/bridge.py

@@ -171,6 +171,7 @@ def mark_dirty(self) -> None:
         self._adapter = None
         self._mcp_status_cache = None
         if self._session_manager:
+            self._session_manager.clear_session_ids()
             manager = self._session_manager
             self._session_manager = None
             _async_safe_manager_shutdown(manager)

components/runners/ambient-runner/ambient_runner/bridges/gemini_cli/session.py

@@ -372,6 +372,19 @@ def _restore_session_ids(self) -> None:
         except (OSError, json.JSONDecodeError):
             logger.debug("Could not restore session IDs from %s", path, exc_info=True)
 
+    def clear_session_ids(self) -> None:
+        """Clear persisted session IDs from disk (e.g., after workflow change)."""
+        self._session_ids.clear()
+        path = self._session_ids_path()
+        if path:
+            try:
+                path.unlink()
+                logger.info("Cleared stale Gemini session IDs from %s", path)
+            except FileNotFoundError:
+                pass
+            except OSError:
+                logger.debug("Could not remove session IDs at %s", path, exc_info=True)
+
     async def interrupt(self, thread_id: str) -> None:
         """Interrupt the active worker for a thread."""
         worker = self._workers.get(thread_id)

components/runners/ambient-runner/tests/test_bridge_gemini_cli.py

@@ -141,6 +141,7 @@ def test_mark_dirty_shuts_down_session_manager(self):
         """mark_dirty() should trigger shutdown on the old session manager."""
         bridge = GeminiCLIBridge()
         mock_manager = AsyncMock()
+        mock_manager.clear_session_ids = MagicMock()
         bridge._session_manager = mock_manager
 
         # We need a running event loop for mark_dirty to schedule shutdown
@@ -150,6 +151,7 @@ def test_mark_dirty_shuts_down_session_manager(self):
                 mock_future.return_value = MagicMock()
                 bridge.mark_dirty()
 
+        mock_manager.clear_session_ids.assert_called_once()
         assert bridge._session_manager is None