feat(isr): add latest-frame storage for ISR cropping

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

jobs/storage.py

@@ -39,6 +39,7 @@ class JobStorage:
     def __init__(self) -> None:
         self._jobs: Dict[str, JobInfo] = {}
         self._tracks: Dict[str, Dict[int, list]] = {} # job_id -> {frame_idx -> tracks}
+        self._latest_frames: Dict[str, any] = {}  # job_id -> np.ndarray
         self._lock = RLock()
 
     def create(self, job: JobInfo) -> None:
@@ -69,6 +70,14 @@ class JobStorage:
                     summary[idx] = count
             return summary
 
+    def store_latest_frame(self, job_id: str, frame) -> None:
+        """Store the most recent frame for ISR cropping (no lock needed, single writer)."""
+        self._latest_frames[job_id] = frame
+
+    def get_latest_frame(self, job_id: str):
+        """Get the most recent frame for ISR cropping."""
+        return self._latest_frames.get(job_id)
+
     def get(self, job_id: str) -> Optional[JobInfo]:
         with self._lock:
             return self._jobs.get(job_id)
@@ -85,6 +94,7 @@ class JobStorage:
         with self._lock:
             self._jobs.pop(job_id, None)
             self._tracks.pop(job_id, None)
+            self._latest_frames.pop(job_id, None)
         shutil.rmtree(get_job_directory(job_id), ignore_errors=True)
 
     def cleanup_expired(self, max_age: timedelta) -> None:
@@ -115,3 +125,9 @@ def set_track_data(job_id: str, frame_idx: int, tracks: list) -> None:
 
 def get_track_summary(job_id: str) -> dict:
     return get_job_storage().get_track_summary(job_id)
+
+def store_latest_frame(job_id: str, frame) -> None:
+    get_job_storage().store_latest_frame(job_id, frame)
+
+def get_latest_frame(job_id: str):
+    return get_job_storage().get_latest_frame(job_id)