feat: add workflow action outcomes and tracing

backend/services/workflow_engine.py

@@ -2,8 +2,11 @@
 
 from __future__ import annotations
 
+import json
 import re
+from copy import deepcopy
 from dataclasses import dataclass
+from hashlib import sha256
 from typing import Any
 
 from services.node_specs import normalize_graph
@@ -32,6 +35,7 @@ class AgentStageConfig:
 class WorkflowEngine:
     def __init__(self, graph: dict[str, Any]):
         self.graph = normalize_graph(graph)
+        self.revision = self._revision_for(self.graph)
         self.settings = self.graph.get("settings") or {}
         self.nodes: dict[str, dict] = {
             str(node["id"]): node
@@ -48,6 +52,29 @@ class WorkflowEngine:
             None,
         )
 
+    @staticmethod
+    def _revision_for(normalized_graph: dict[str, Any]) -> str:
+        """Hash the exact normalized graph used by this runtime."""
+
+        canonical = json.dumps(
+            normalized_graph,
+            ensure_ascii=False,
+            sort_keys=True,
+            separators=(",", ":"),
+        ).encode("utf-8")
+        return f"sha256:{sha256(canonical).hexdigest()}"
+
+    def session_metadata(self) -> dict[str, Any]:
+        """Pin a conversation to an immutable, inspectable graph snapshot."""
+
+        return {
+            "workflow": {
+                "revision": self.revision,
+                "specVersion": self.graph.get("specVersion"),
+                "snapshot": deepcopy(self.graph),
+            }
+        }
+
     def has_graph(self) -> bool:
         return bool(self.start_id)