Fix parallel worker chat log orphans

Skip persisted tool-result files for BACKGROUND contexts, remove ephemeral direct parallel worker chat folders during cleanup, and ignore chat directories without chat.json during startup loading.

Add focused regressions for background output persistence, parallel worker cleanup, and orphan directory loading.

extensions/python/hist_add_tool_result/AGENTS.md

@@ -12,6 +12,7 @@
 
 - Preserve tool result traceability without leaking secrets.
 - Keep file artifacts inside expected runtime/user-owned paths.
+- Skip BACKGROUND contexts; background workers must remain ephemeral and must not create chat message files.
 
 ## Work Guidance
 

extensions/python/hist_add_tool_result/_90_save_tool_call_file.py

@@ -1,4 +1,5 @@
 from typing import Any
+from agent import AgentContextType
 from helpers.extension import Extension
 from helpers import files, persist_chat
 import os, re
@@ -9,6 +10,9 @@ class SaveToolCallFile(Extension):
     def execute(self, data: dict[str, Any] | None = None, **kwargs):
         if not self.agent:
             return
+
+        if self.agent.context.type == AgentContextType.BACKGROUND:
+            return
             
         if not data:
             return