fix: preserve parent agent's tool list after subagent delegation (#1778)

Save and restore the process-global _last_resolved_tool_names in
_run_single_child() so the parent's execute_code sandbox generates
correct tool imports after delegation completes.

The global was already mostly mitigated (run_agent.py passes
enabled_tools via self.valid_tool_names), but the global itself
remained corrupted — a footgun for any code that reads it directly.

Co-authored-by: shane9coy <shane9coy@users.noreply.github.com>

tools/delegate_tool.py

@@ -171,6 +171,11 @@ def _build_child_agent(
     model on OpenRouter while the parent runs on Nous Portal).
     """
     from run_agent import AIAgent
+    import model_tools
+
+    # Save the parent's resolved tool names before the child agent can
+    # overwrite the process-global via get_tool_definitions().
+    _saved_tool_names = list(model_tools._last_resolved_tool_names)
 
     # When no explicit toolsets given, inherit from parent's enabled toolsets
     # so disabled tools (e.g. web) don't leak to subagents.
@@ -365,6 +370,10 @@ def _run_single_child(
         }
 
     finally:
+        # Restore the parent's tool names so the process-global is correct
+        # for any subsequent execute_code calls or other consumers.
+        model_tools._last_resolved_tool_names = _saved_tool_names
+
         # Unregister child from interrupt propagation
         if hasattr(parent_agent, '_active_children'):
             try: