result['error'] and result['final_response'] are independently settable
keys that only coincidentally share _COMPRESSION_TIMEOUT_FINAL_RESPONSE
today; assert the actionable substring instead so a benign prefix or
rewording does not break the terminal-contract test.
Salvaged from #98741, composed on top of the merged #98424 preflight
fail-closed boundary. A host-ceiling compression timeout is now a typed,
thread-safe outcome consumed by every automatic caller:
- conversation_compression.py: threading.local + per-agent lock timeout
state (mark/reset/read helpers) upgrading #98424's simple attribute
where overlapping automatic/manual compression entrypoints matter;
the _last_compression_timed_out attribute stays as compat mirror.
- conversation_loop.py: the mid-turn pre-API pass and the provider
overflow (413/400 context_length_exceeded) recovery path end the turn
with the typed compression_exhausted recovery contract instead of
re-sending the unchanged oversized request and re-entering compression
in the same turn.
- run_agent.py/turn_context.py: forwarder resets the typed state per
attempt; the #98424 turn-start check reads it through the typed helper.
Tests: thread-safety/atomicity of the state helpers, overflow-recovery
non-re-entry, and typed terminal result.
kshitijk4poor