fix(proxy): quarantine silent HTTP bridge sessions (takeover of #1405)

[Soju06]

Summary

First-party takeover of #1405 by @WangErgouaaaa — quarantine is the maintainer-chosen direction for silent HTTP-bridge sessions (decided 08-04, over the account-health penalty alternative #1574), and the author has been unresponsive since 07-20 across two review rounds and a takeover offer. Supersedes #1405. The original commit's quarantine-window concept, per-key deadline registry with pruning/size-cap eviction, and event wording are carried forward with attribution (Co-authored-by: WangErgouaaaa <117421439+WangErgouaaaa@users.noreply.github.com>); the rejected pieces (5s response.created timeout, raw-HTTP fallback window, two new settings) are replaced per the 07-24/08-06 review findings.

Related: #1534 (production evidence; its reported fully eventless full-resend flavor was already fixed by the merged #1563 — this PR covers the remainder that #1563 and #1394 leave open: the events-flowing wedge, the in-memory reuse path, and the repeated-wedge case), #1580 (the deferred-reasoning P1 is honored: quarantine never keys on mere event silence during a live owned turn), #1410.

Trigger (proof-based, never a live-turn timeout)

Evaluated only when a request is already being failed or its session retired:

1. Wedged reattach (immediate): a pending request with a proxy-injected previous_response_id that sent response.create, observed upstream response events, but never had response.created assigned. This is the shape that actually wedged production (HTTP-bridge reattach stalls with no response.created and needs a client restart to recover #1534/fix(http-bridge): unstarve the stuck-gate watchdog on silent upstreams (follow-up to #1394) #1410) — the response_event_count == 0 gates in the eventless watchdog (fix(http-bridge): stabilize silent and clean-close recovery #1394) and the fenced anchor clear (fix(proxy): clear durable bridge anchor after stuck eventless timeout #1563) never trip on it, and replay is refused because model output was seen. Hooked at the reader failure/retire funnel and the stale-gate-holder cleanup.
2. Repeated eventless timeouts: two consecutive missing_response_created_timeout retires for the same session key. The first stays on the merged fix(http-bridge): stabilize silent and clean-close recovery #1394 recovery path (bounded pre-created retry + fix(proxy): clear durable bridge anchor after stuck eventless timeout #1563 fenced anchor clear).

Any request whose response.created was observed is excluded by construction — a deferred-reasoning stream with long legitimate gaps can never be quarantined (unit-tested negative).

Effect (session-scoped, account-neutral)

• Quarantined sessions are excluded from re-attach/session-reuse selection; a new lookup detaches them and proceeds on a fresh session.
• While the key is quarantined, fresh-reattach durable-anchor injection is skipped for full-resend payloads (fresh_reattach_anchor_skipped_quarantined): the client's own payload carries the whole conversation and goes upstream unanchored on the fresh path that HTTP-bridge reattach stalls with no response.created and needs a client restart to recover #1534's evidence shows working. Delta-only payloads keep the anchor — it is their only way to convey prior context (same boundary as fix(proxy): clear durable bridge anchor after stuck eventless timeout #1563).
• Zero account-health writes; durable continuity ownership is preserved on the fresh path.

Expiry (bounded, no leak)

In-memory only — no durable rows, no janitor, no migration, no settings (fix-class, default-on). Cleared on a completed response for the key (alongside the retry-circuit clear); otherwise a 600s TTL (aligned with the retry circuit's max backoff), prune-on-touch, and a 1024-entry size cap with oldest-first eviction.

OpenSpec

openspec/changes/quarantine-silent-bridge-sessions/ (responses-api-compat delta, 7 scenarios incl. the deferred-reasoning negative and the delta-only-anchor protection). openspec validate quarantine-silent-bridge-sessions --strict and openspec validate --specs --strict (49/49) pass.

Test evidence

• Integration regression modeling HTTP-bridge reattach stalls with no response.created and needs a client restart to recover #1534 (tests/integration/test_http_responses_bridge.py): reattach injects the durable anchor (resp_bridge_custom_1), upstream streams reasoning deltas but never response.created, the turn fails and the key is quarantined; the next full-resend request is sent with no previous_response_id and completes 200 on a fresh connect, and the completed response clears the quarantine. Verified the test fails with quarantine neutralized — the third attempt rebuilds the identical wedged reattach and fails again, reproducing the HTTP-bridge reattach stalls with no response.created and needs a client restart to recover #1534 loop.
• Unit coverage: predicate truth table (8 shapes), TTL expiry, size bound, 2-strike threshold with completion reset, reuse-gate exclusion, reader-failure trigger (positive + created-assigned negative), stale-gate-holder trigger, and a real reader-loop missing_response_created_timeout run recording exactly one strike without quarantining.
• Gates: ruff check/format, ty (clean), scripts/check_proxy_architecture.py (no budget raised — new logic lives in un-ratcheted quarantine.py; mixin.py/service.py untouched), tests/unit/test_proxy_http_bridge.py 488 passed, adjacent bridge suites 298 passed, full tests/unit 5684 passed, tests/integration/test_http_responses_bridge.py 122 passed.

🤖 Generated with Claude Code

Post-review hardening (b473212)

Two fixes from the adversarial verification pass, each with a regression test: the session-object quarantine flag now resets on clear (a surviving session becomes reusable once a completed response disproves the wedge), and a TTL-expired first eventless strike can no longer be resurrected into a "consecutive" second strike (prune runs before increment).

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Treat quarantined local sessions as absent during anchor planning

When stale-gate cleanup quarantines a session while a sibling request keeps it live, _http_bridge_has_live_local_session still returns true because its checks in owner_forwarding.py ignore session.quarantined. That makes fresh_reattach_can_use_durable_anchor false before this quarantine check is reached; the later lookup then rejects and detaches the session, so a delta-only continuation is sent on a fresh connection without the durable anchor and loses its prior conversation context. Make the live-local preflight use the same quarantine eligibility as session reuse.

AGENTS.md reference: AGENTS.md:L129-L132

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[chatgpt-codex-connector]

Clear live session flags when pruning quarantine entries

When the 600-second TTL elapses—or the size cap evicts an entry—this removes only the registry record and leaves the corresponding live session's quarantined flag set. A session that survived stale-gate cleanup without a later completion therefore remains permanently ineligible for reuse even though the documented quarantine window expired; this is observable for Codex sessions whose configured idle TTL can exceed 600 seconds. Expiry/eviction must also clear or stop relying on the per-session flag.

AGENTS.md reference: AGENTS.md:L24-L27

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