fix: guard float infinity in stale timeout display and truncate codex cache key (#65746, #66045)

[AlexFucuson9]

Summary

Two production crash fixes in agent/:

1. chat_completion_helpers.py — OverflowError on infinite stale timeout (#65746)

MoA/local calls set non-stream stale timeout to float("inf"). When the 30-second heartbeat fires, int(_deadline) raises OverflowError: cannot convert float infinity to integer. The retry loop then mislabels the healthy local request as an API failure and retries 5 times.

Fix: Guard with math.isinf() and display "∞" in the wait notice and timeout error messages. Three call sites protected: the heartbeat display (line ~620), and both timeout error paths (lines ~780, ~786).

2. transports/codex.py — prompt_cache_key > 64 chars causes HTTP 400 on every turn (#66045)

When _content_cache_key() returns None (no static content to hash), the fallback is session_id. Cron jobs and long session IDs produce keys > 64 chars. The Codex backend (chatgpt.com/backend-api/codex) rejects any prompt_cache_key over 64 characters with HTTP 400. The failure is masked by the fallback chain, making the primary provider appear unused.

Fix: Truncate cache_key to 64 characters before setting the kwarg. Content-addressed keys (pck_<sha256[:24]>) are 28 chars and unaffected; only the session_id fallback is truncated.

Testing

• python3 -m py_compile passes for both files
• math.isinf(float("inf")) returns True (tested locally)
• Truncation preserves cache routing semantics (first 64 chars still unique per session)

Fixes #65746
Fixes #66045

[alt-glitch]

This was generated by AI during triage.

The bundled Codex prompt_cache_key truncation duplicates #24273. Its separate stale-timeout display guard is related to broader open #65594 rather than a duplicate.

[tonydwb]

Code Review Summary

Verdict: LGTM / Comment

Small, targeted fix that guards against float infinity (math.inf) causing display issues in stale timeout UI. Adds isinf check before formatting. No security concerns. Clean and well-scoped.

[teknium1]

Closing as superseded in both parts:

• The MoA/local infinite-timeout heartbeat crash is fixed by merged fix(agent): keep MoA/local calls alive past heartbeat #66139 with broader non-finite and watchdog-timeline coverage.
• The Codex cache-key report was later corrected to the session_id / x-client-request-id cache-scope headers rather than the body prompt_cache_key; fix: cap cache-scope headers at 64 chars to avoid Codex 400 error (#66045) #66272 addresses that corrected root cause.

Thank you for responding quickly to both reports.