Summary

Fixes #14894

The post_llm_call plugin hook was invoked after _persist_session(), so any response overrides applied by plugins were never captured in the persisted session history. This caused a mismatch between the final_response returned to the caller and the history stored in SQLite/JSON logs.

Root Cause

In run_conversation():

1. _persist_session(messages, conversation_history) writes to DB
2. post_llm_call hook fires — plugin can modify final_response

The hook result was never re-persisted.

Changes

run_agent.py — run_conversation():

• Moved _persist_session() to fire after the post_llm_call hook block
• Added support for plugins to return {"override_response": "..."} dicts
• When an override is returned, both final_response and the last assistant message are updated before persistence
• Restored the turn-exit diagnostic log block in its original position

Testing

• The hook block is guarded by try/except — plugin failures cannot break persistence
• _persist_session() still runs unconditionally after the hook
• Turn-exit diagnostic logging is preserved (no regression)
• Existing test_plugins.py tests remain compatible (invoke_hook return value was previously ignored)

Checklist

• Follows Conventional Commits format
• Single logical change
• No breaking changes
• Backward compatible (plugins that don't return override_response work as before)