fix(agent): guard float infinity to int conversions in stale timeout watchdogs

[AntonIXO]

Summary

Prevent OverflowError: cannot convert float infinity to integer when the non-streaming API watchdog formats an unbounded timeout.

Root cause / reproduction

_compute_non_stream_stale_timeout() intentionally returns float("inf") for local endpoints such as moa://local. After 100 polling intervals (100 × 0.3s ≈ 30s), the wait-notice heartbeat formatted that value with int(_deadline), aborting an otherwise-live MoA request. The outer conversation loop then retried, producing failures at approximately 30s, 62s, and 97s.

This PR now includes a deterministic regression test that drives the exact 100-poll MoA heartbeat without waiting 30 seconds. Before the fix it fails at chat_completion_helpers.py with the reported OverflowError; after the fix it emits auto-reconnect at never and leaves the request alive.

Fix

Guard infinite timeout formatting in the wait-notice path and the related TTFB, stream-idle, and stale-timeout diagnostic paths.

Relation to #64924

This overlaps with #64924 on the primary wait-notice cast. It is broader rather than independent: it also guards the related watchdog diagnostic/error formatting and adds direct MoA regression coverage for the observed 30-second failure.

Verification

• tests/agent/test_infinite_stale_timeout_wait_notice.py: 1 passed
• tests/agent/test_reasoning_stale_timeout_floor.py: 57 passed
• tests/agent/test_codex_ttfb_watchdog.py: 13 passed

[alt-glitch]

This was generated by AI during triage.

Related to #64924: both guard infinite timeout formatting in chat_completion_helpers.py, but this PR additionally covers TTFB, idle, and stale-timeout error paths, so it is a broader overlapping fix rather than a duplicate.

[tonydwb]

Code Review Summary

Verdict: Comment

Scope

• 1 file (agent/chat_completion_helpers.py), +10/-3 lines
• Guards float-to-int conversions when deadline/timeout values are infinity.

Quality

• F-strings with conditional formatting: display "inf" instead of crashing on int(float('inf')).
• Consistent with the infinite-wait-deadline fix in PR 65606 (same file context).

Looks Good

• Small, correct fix for a real edge case.

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Reviewed by Hermes Agent

[teknium1]

Superseded by #66139, which has now merged the same MoA/local heartbeat fix with the full 100-poll regression shape from this PR, plus accurate finite-watchdog selection and fail-open notice construction.

#66139 explicitly credits this PR for the full-heartbeat regression approach. Thank you for the production evidence and coverage.