Store IPFS CID in database for DAG outputs

Properly unpack cache_manager.put() tuple to get IPFS CID and store
it in PostgreSQL via database.create_cache_item(). This fixes the
"Output has no IPFS CID - cannot publish" error when publishing
from L1 to L2.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tasks.py

@@ -333,8 +333,26 @@ def execute_dag(self, dag_json: str, run_id: str = None) -> dict:
     if result.output_path and result.output_path.exists():
         output_hash = file_hash(result.output_path)
 
-        # Store in cache_manager for proper tracking
-        cached = cache_manager.put(result.output_path, node_type="dag_output")
+        # Store in cache_manager for proper tracking (returns tuple)
+        cached, ipfs_cid = cache_manager.put(result.output_path, node_type="dag_output")
+
+        # Store in database (for L2 to query IPFS CID)
+        import asyncio
+        import database
+
+        async def save_to_db():
+            if database.pool is None:
+                await database.init_db()
+            await database.create_cache_item(output_hash, ipfs_cid)
+
+        try:
+            loop = asyncio.get_event_loop()
+            if loop.is_running():
+                asyncio.ensure_future(save_to_db())
+            else:
+                loop.run_until_complete(save_to_db())
+        except RuntimeError:
+            asyncio.run(save_to_db())
 
         # Record activity for deletion tracking
         input_hashes = []