Fix NoneType subscript error in record_run

- Add get_asset_by_name_tx for transaction-aware asset lookup
- Use transaction connection instead of separate connection
- Prevents race condition where asset might not be visible

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

db.py

@@ -464,6 +464,19 @@ async def asset_exists_by_name_tx(conn, name: str) -> bool:
     )
 
 
+async def get_asset_by_name_tx(conn, name: str) -> Optional[dict]:
+    """Get asset by name within a transaction."""
+    row = await conn.fetchrow(
+        """SELECT name, content_hash, ipfs_cid, asset_type, tags, metadata, url,
+                  provenance, description, origin, owner, created_at, updated_at
+           FROM assets WHERE name = $1""",
+        name
+    )
+    if row:
+        return _parse_asset_row(row)
+    return None
+
+
 async def create_asset_tx(conn, asset: dict) -> dict:
     """Create a new asset within a transaction."""
     row = await conn.fetchrow(