Add bidirectional sync between HF Space and Modal volume

On refresh, the Space now pushes local submissions missing from the
Modal volume back to it, in addition to pulling. This restores the
volume automatically after a Modal crash or wipe.

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

app.py

@@ -23,7 +23,7 @@ from src.hackathon import (
     score_red_with_pairwise,
     stimulus_key,
 )
-from src.hackathon.modal_client import fetch_volume_submissions, is_modal_enabled
+from src.hackathon.modal_client import fetch_volume_submissions, is_modal_enabled, push_submissions_to_volume
 from src.hackathon.validation import (
     MODEL_REGISTRY_ENV,
     BLUE_MODEL_REGISTRY_ENV,
@@ -283,22 +283,29 @@ def _build_pairwise_df(results: list[dict]) -> pd.DataFrame:
 
 
 def _sync_team_from_volume(team: str):
-    """Sync a single team's submissions from the Modal volume."""
+    """Bidirectional sync between the Modal volume and local/HF storage."""
     if not is_modal_enabled():
         return
     try:
         volume_subs = fetch_volume_submissions(team=team)
-        if not volume_subs:
-            return
         existing = load_submissions(team)
+
+        # Pull: Modal volume → local/HF
+        volume_ids = {s.get("submission_id") for s in volume_subs}
         existing_ids = {s.get("submission_id") for s in existing}
-        missing = [s for s in volume_subs if s.get("submission_id") not in existing_ids]
-        if missing:
-            for sub in missing:
+        missing_locally = [s for s in volume_subs if s.get("submission_id") not in existing_ids]
+        if missing_locally:
+            for sub in missing_locally:
                 append_submission(team, sub)
-            print(f"Synced {len(missing)} missing {team} submission(s) from Modal volume.")
+            print(f"Pulled {len(missing_locally)} missing {team} submission(s) from Modal volume.")
+
+        # Push: local/HF → Modal volume
+        missing_on_volume = [s for s in existing if s.get("submission_id") not in volume_ids]
+        if missing_on_volume:
+            result = push_submissions_to_volume(missing_on_volume)
+            print(f"Pushed {result.get('added', 0)} missing {team} submission(s) to Modal volume.")
     except Exception as exc:
-        print(f"Warning: failed to sync {team} submissions from Modal volume: {exc}")
+        print(f"Warning: failed to sync {team} submissions: {exc}")
 
 
 def refresh_blue_leaderboard():

src/hackathon/modal_client.py

@@ -153,3 +153,13 @@ def fetch_volume_submissions(team: str | None = None) -> list[dict[str, Any]]:
     """
     fn = _get_modal_function("list_submissions")
     return fn.remote(team=team)
+
+
+def push_submissions_to_volume(submissions: list[dict[str, Any]]) -> dict[str, int]:
+    """Push local submissions to the Modal volume.
+
+    Used to backfill the volume after a Modal crash or volume wipe.
+    Returns {"added": N, "skipped": M}.
+    """
+    fn = _get_modal_function("backfill_submissions")
+    return fn.remote(submissions=submissions)