fix(agent): close interrupted early-persisted user turns

Track text-only user messages that were flushed before the turn loop completes, then materialize an interrupted assistant placeholder on the next request so session history stays legal and later turns do not skip their own assistant reply.

Made-with: Cursor

nanobot/agent/loop.py

@@ -129,6 +129,7 @@ class AgentLoop:
     """
 
     _RUNTIME_CHECKPOINT_KEY = "runtime_checkpoint"
+    _PENDING_USER_TURN_KEY = "pending_user_turn"
 
     def __init__(
         self,
@@ -618,6 +619,8 @@ class AgentLoop:
             session = self.sessions.get_or_create(key)
             if self._restore_runtime_checkpoint(session):
                 self.sessions.save(session)
+            if self._restore_pending_user_turn(session):
+                self.sessions.save(session)
 
             session, pending = self.auto_compact.prepare_session(session, key)
 
@@ -653,6 +656,8 @@ class AgentLoop:
         session = self.sessions.get_or_create(key)
         if self._restore_runtime_checkpoint(session):
             self.sessions.save(session)
+        if self._restore_pending_user_turn(session):
+            self.sessions.save(session)
 
         session, pending = self.auto_compact.prepare_session(session, key)
 
@@ -702,6 +707,7 @@ class AgentLoop:
         user_persisted_early = False
         if isinstance(msg.content, str) and msg.content.strip():
             session.add_message("user", msg.content)
+            self._mark_pending_user_turn(session)
             self.sessions.save(session)
             user_persisted_early = True
 
@@ -723,6 +729,7 @@ class AgentLoop:
         # Skip the already-persisted user message when saving the turn
         save_skip = 1 + len(history) + (1 if user_persisted_early else 0)
         self._save_turn(session, all_msgs, save_skip)
+        self._clear_pending_user_turn(session)
         self._clear_runtime_checkpoint(session)
         self.sessions.save(session)
         self._schedule_background(self.consolidator.maybe_consolidate_by_tokens(session))
@@ -840,6 +847,12 @@ class AgentLoop:
         session.metadata[self._RUNTIME_CHECKPOINT_KEY] = payload
         self.sessions.save(session)
 
+    def _mark_pending_user_turn(self, session: Session) -> None:
+        session.metadata[self._PENDING_USER_TURN_KEY] = True
+
+    def _clear_pending_user_turn(self, session: Session) -> None:
+        session.metadata.pop(self._PENDING_USER_TURN_KEY, None)
+
     def _clear_runtime_checkpoint(self, session: Session) -> None:
         if self._RUNTIME_CHECKPOINT_KEY in session.metadata:
             session.metadata.pop(self._RUNTIME_CHECKPOINT_KEY, None)
@@ -906,9 +919,30 @@ class AgentLoop:
                 break
         session.messages.extend(restored_messages[overlap:])
 
+        self._clear_pending_user_turn(session)
         self._clear_runtime_checkpoint(session)
         return True
 
+    def _restore_pending_user_turn(self, session: Session) -> bool:
+        """Close a turn that only persisted the user message before crashing."""
+        from datetime import datetime
+
+        if not session.metadata.get(self._PENDING_USER_TURN_KEY):
+            return False
+
+        if session.messages and session.messages[-1].get("role") == "user":
+            session.messages.append(
+                {
+                    "role": "assistant",
+                    "content": "Error: Task interrupted before a response was generated.",
+                    "timestamp": datetime.now().isoformat(),
+                }
+            )
+            session.updated_at = datetime.now()
+
+        self._clear_pending_user_turn(session)
+        return True
+
     async def process_direct(
         self,
         content: str,