When the TUI exits while the post-turn background review fork is still
mid-request, every further API attempt raises 'cannot schedule new
futures after interpreter shutdown'. The conversation loop treated this
as a retryable API error: un-gated ❌ prints leaked onto the user's
shell AFTER the TUI exited (call #4, #5, #6...) and the loop retried a
doomed request until the interpreter froze the thread.
Fix the class, not the site:
- tools/interpreter_shutdown.py: single shared shutdown predicate
(matches both CPython message variants + sys.is_finalizing()).
- cron/scheduler.py, agent/tool_executor.py: existing per-site
predicates now delegate to the shared home (tool_executor previously
matched only the fuller variant).
- agent/conversation_loop.py: inner retry handler recognizes the
shutdown signal and abandons the turn — one log warning, no print,
no traceback, no debug dump, no retry; outer handler gets the same
guard for shutdown errors raised outside the API call.
- The outer handler's bare print() now honors suppress_status_output
(set by the background-review fork) instead of bypassing it.
Refs #55924#58720 (same class in cron delivery), adjacent to #90683.
