feat(dashboard): persist task state to disk for restart recovery

- Add TASK_STATUS_DIR for task state JSON files
- Lifespan startup: restore task states from disk
- Task completion/failure: write state to disk
- Task cancellation: delete persisted state

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web_dashboard/backend/main.py

@@ -23,6 +23,8 @@ from pydantic import BaseModel
 REPO_ROOT = Path(__file__).parent.parent.parent
 # Use the currently running Python interpreter
 ANALYSIS_PYTHON = Path(sys.executable)
+# Task state persistence directory
+TASK_STATUS_DIR = Path(__file__).parent / "data" / "task_status"
 
 
 # ============== Lifespan ==============
@@ -33,6 +35,16 @@ async def lifespan(app: FastAPI):
     app.state.active_connections: dict[str, list[WebSocket]] = {}
     app.state.task_results: dict[str, dict] = {}
     app.state.analysis_tasks: dict[str, asyncio.Task] = {}
+
+    # Restore persisted task states from disk
+    TASK_STATUS_DIR.mkdir(parents=True, exist_ok=True)
+    for f in TASK_STATUS_DIR.glob("*.json"):
+        try:
+            data = json.loads(f.read_text())
+            app.state.task_results[data["task_id"]] = data
+        except Exception:
+            pass
+
     yield
 
 
@@ -86,7 +98,21 @@ def _load_from_cache(mode: str) -> Optional[dict]:
         return None
 
 
-def _save_to_cache(mode: str, data: dict):
+def _save_task_status(task_id: str, data: dict):
+    """Persist task state to disk"""
+    try:
+        TASK_STATUS_DIR.mkdir(parents=True, exist_ok=True)
+        (TASK_STATUS_DIR / f"{task_id}.json").write_text(json.dumps(data, ensure_ascii=False))
+    except Exception:
+        pass
+
+
+def _delete_task_status(task_id: str):
+    """Remove persisted task state from disk"""
+    try:
+        (TASK_STATUS_DIR / f"{task_id}.json").unlink(missing_ok=True)
+    except Exception:
+        pass
     try:
         CACHE_DIR.mkdir(parents=True, exist_ok=True)
         cache_path = _get_cache_path(mode)
@@ -346,6 +372,8 @@ async def start_analysis(request: AnalysisRequest):
                 app.state.task_results[task_id]["status"] = "failed"
                 app.state.task_results[task_id]["error"] = error_msg
 
+            _save_task_status(task_id, app.state.task_results[task_id])
+
         except Exception as e:
             cancel_event.set()
             app.state.task_results[task_id]["status"] = "failed"
@@ -355,6 +383,8 @@ async def start_analysis(request: AnalysisRequest):
             except Exception:
                 pass
 
+            _save_task_status(task_id, app.state.task_results[task_id])
+
         await broadcast_progress(task_id, app.state.task_results[task_id])
 
     task = asyncio.create_task(run_analysis())
@@ -425,6 +455,9 @@ async def cancel_task(task_id: str):
     except Exception:
         pass
 
+    # Remove persisted task state
+    _delete_task_status(task_id)
+
     return {"task_id": task_id, "status": "cancelled"}