fix: keep pooled live snapshots cancellation-safe (#137)

src/main.py

@@ -26,11 +26,23 @@ from src.views import router as frontend_router
 
 @asynccontextmanager
 async def lifespan(_app: FastAPI):
+    global _live_snapshot_task
     gitea_proxy.start_client()
     try:
         yield
     finally:
-        await gitea_proxy.stop_client()
+        task = _live_snapshot_task
+        if task is not None and not task.done():
+            task.cancel()
+            try:
+                await task
+            except asyncio.CancelledError:
+                pass
+        try:
+            await gitea_proxy.stop_client()
+        finally:
+            if _live_snapshot_task is task:
+                _live_snapshot_task = None
 
 
 app = FastAPI(title="Stackchain Dashboard", lifespan=lifespan)
@@ -251,15 +263,22 @@ async def _build_live_snapshot() -> dict:
     }
 
 
+async def _build_live_snapshot_before_deadline() -> dict:
+    async with asyncio.timeout(CONTEXT_TIMEOUT_SECONDS):
+        return await _build_live_snapshot()
+
+
 @app.get("/api/v1/live")
 async def live_snapshot() -> JSONResponse:
     """Return a fresh, section-aware snapshot; join only an active identical load."""
     global _live_snapshot_task
     if _live_snapshot_task is None or _live_snapshot_task.done():
-        _live_snapshot_task = asyncio.create_task(_build_live_snapshot())
+        _live_snapshot_task = asyncio.create_task(
+            _build_live_snapshot_before_deadline()
+        )
     task = _live_snapshot_task
     try:
-        result = await asyncio.wait_for(task, timeout=CONTEXT_TIMEOUT_SECONDS)
+        result = await asyncio.shield(task)
         return JSONResponse(result)
     except TimeoutError:
         return JSONResponse(