Store provenance on IPFS instead of local files

- Add add_json() to ipfs_client for storing JSON data
- Update render_effect task to store provenance on IPFS
- Update execute_dag task to store DAG provenance on IPFS
- Add provenance_cid field to RunStatus model
- Extract provenance_cid from task results

Provenance is now immutable and content-addressed, enabling:
- Cross-L2 verification
- Bitcoin timestamping for dispute resolution
- Complete audit trail on IPFS

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

tasks.py

@@ -237,7 +237,6 @@ def render_effect(self, input_hash: str, effect_name: str, output_name: str) ->
         "output": {
             "name": output_name,
             "content_hash": output_hash,
-            "local_path": str(result)
         },
         "inputs": [
             {"content_hash": input_hash}
@@ -249,10 +248,14 @@ def render_effect(self, input_hash: str, effect_name: str, output_name: str) ->
         }
     }
 
-    # Save provenance
-    provenance_path = result.with_suffix(".provenance.json")
-    with open(provenance_path, "w") as f:
-        json.dump(provenance, f, indent=2)
+    # Store provenance on IPFS
+    import ipfs_client
+    provenance_cid = ipfs_client.add_json(provenance)
+    if provenance_cid:
+        provenance["provenance_cid"] = provenance_cid
+        logger.info(f"Stored provenance on IPFS: {provenance_cid}")
+    else:
+        logger.warning("Failed to store provenance on IPFS")
 
     return provenance
 
@@ -339,6 +342,39 @@ def execute_dag(self, dag_json: str, run_id: str = None) -> dict:
                 run_id=run_id,
             )
 
+    # Build provenance
+    input_hashes_for_provenance = []
+    for node_id, node in dag.nodes.items():
+        if node.node_type == NodeType.SOURCE or str(node.node_type) == "SOURCE":
+            content_hash = node.config.get("content_hash")
+            if content_hash:
+                input_hashes_for_provenance.append({"content_hash": content_hash})
+
+    provenance = {
+        "task_id": self.request.id,
+        "run_id": run_id,
+        "rendered_at": datetime.now(timezone.utc).isoformat(),
+        "output": {
+            "content_hash": output_hash,
+        },
+        "inputs": input_hashes_for_provenance,
+        "dag": dag_json,  # Full DAG definition
+        "execution": {
+            "execution_time": result.execution_time,
+            "nodes_executed": result.nodes_executed,
+            "nodes_cached": result.nodes_cached,
+        }
+    }
+
+    # Store provenance on IPFS
+    import ipfs_client
+    provenance_cid = ipfs_client.add_json(provenance)
+    if provenance_cid:
+        provenance["provenance_cid"] = provenance_cid
+        logger.info(f"Stored DAG provenance on IPFS: {provenance_cid}")
+    else:
+        logger.warning("Failed to store DAG provenance on IPFS")
+
     # Build result
     return {
         "success": True,
@@ -351,6 +387,7 @@ def execute_dag(self, dag_json: str, run_id: str = None) -> dict:
         "node_results": {
             node_id: str(path) for node_id, path in result.node_results.items()
         },
+        "provenance_cid": provenance_cid,
     }