fix(codex): resolve peer-review findings R1-R6 and T1-T2

- R1: use herdr send-keys C-c for graceful stop
- R2: preserve JSONL fallback discovery when database is empty
- R3: apply workspace-scoped SQLite query before bounding results
- R4: tighten artifact validation to fail closed on missing/invalid metadata
- R5: verify actual rollout presence before reporting resumable in status
- R6: remove unconditional drift-B backend command fallback
- T1: parameterize artifact metadata regression with verified finder fixture
- T2: seed unmanaged and managed sessions in mock herdr for drift-B testing
- Add final loop review reports (100% PASS)

tests/conftest.py

@@ -655,7 +655,7 @@ elif cmd1 == "agent":
             rollout_file = os.path.join(sessions_dir, f"rollout-001-{session_uuid}.jsonl")
             now_ts = int(time.time())
             with open(rollout_file, "w") as rf:
-                rf.write(json.dumps({"payload": {"cwd": ws_abs, "id": session_uuid}}) + "\\\\n")
+                rf.write(json.dumps({"payload": {"cwd": ws_abs, "id": session_uuid}}) + "\\n")
             conn.execute("INSERT OR REPLACE INTO threads (id, cwd, rollout_path, created_at, updated_at) VALUES (?, ?, ?, ?, ?)", (session_uuid, ws_abs, rollout_file, now_ts, now_ts))
             conn.commit()
             conn.close()