fix: synthetic assistant message on cancel + semantic delegate display names

Author: bkrabach

amplifier_module_loop_basic/__init__.py

@@ -440,8 +440,18 @@ async def execute_single_tool(
 
                         # Register tool with cancellation token for visibility
                         if coordinator:
+                            # Build semantic display name for delegate calls
+                            display_name = tool_name
+                            if tool_name == "delegate":
+                                try:
+                                    _args = args if isinstance(args, dict) else json.loads(args)
+                                    _agent = _args.get("agent", "")
+                                    if _agent:
+                                        display_name = _agent
+                                except (json.JSONDecodeError, TypeError, AttributeError):
+                                    pass
                             coordinator.cancellation.register_tool_start(
-                                tool_call_id, tool_name
+                                tool_call_id, display_name
                             )
 
                         try:
@@ -616,6 +626,14 @@ async def execute_single_tool(
                                     "turn_count": iteration,
                                 },
                             )
+                        # Write synthetic assistant message to close the turn.
+                        # Without this, transcript has tool_results without a closing assistant
+                        # message, triggering FM3 (incomplete_assistant_turn) on resume.
+                        if hasattr(context, "add_message"):
+                            await context.add_message({
+                                "role": "assistant",
+                                "content": "The previous operation was cancelled. Results from completed tools have been preserved.",
+                            })
                         # Re-raise to let the cancellation propagate
                         raise
 
@@ -665,6 +683,14 @@ async def execute_single_tool(
                                 "status": "cancelled",
                             },
                         )
+                        # Write synthetic assistant message to close the turn.
+                        # Without this, transcript has tool_results without a closing assistant
+                        # message, triggering FM3 (incomplete_assistant_turn) on resume.
+                        if hasattr(context, "add_message"):
+                            await context.add_message({
+                                "role": "assistant",
+                                "content": "The previous operation was cancelled. Results from completed tools have been preserved.",
+                            })
                         return final_content
 
                     # Add all tool results to context in original order (deterministic)