Fix#68178
The git-install auto-updater rewrites source while the desktop backend
is live. Because agent/conversation_loop.py is imported lazily on the
first API call, a process can end up running two different commits
spliced together — one commit's AIAgent against another commit's
conversation_loop. When the interface differs, every turn fails
permanently with an AttributeError, and the loop retries indefinitely,
burning provider API calls (576 failures, 149 wasted API calls observed).
Three-prong fix:
1. Circuit-break AttributeError on agent objects: the outer-loop error
classifier now detects AttributeError targeting agent/run_agent
modules and breaks immediately instead of continuing the retry loop.
2. Code skew detection for desktop/serve backend: run_agent.py now
snapshots the checkout revision at import time and exposes a cheap
per-iteration check that the conversation loop uses to refuse new
work with a clear 'restart required' message before the lazy import
can crash.
3. Informative error message: when code skew is detected, the user
gets a clear explanation of the mismatch (boot revision vs current
revision) and actionable guidance to restart the application.
