fix(proxy): bound the detached-session retire sweep's pending_lock wait

[Soju06]

Why

_release_http_bridge_unanchored_handoffs_for_request is a fail-safe sweep on every HTTP-bridge request. For each detached generation it calls _retire_http_bridge_after_drain_if_ready, which acquires that session's pending_lock with no bound. On 2026-09-07 one detached thread_header generation's lock was left permanently unowned by the anyio 4.13 lost-wakeup (#2129), and the production loop probe showed ~100 live request tasks queued behind it inside this sweep:

lock e051dab55010  waiters_deque=100 owner=None  blocked_tasks=53
    x52  helpers.py:_release_http_bridge_unanchored_handoffs_for_request:2729 > request_submit.py:_retire_http_bridge_after_drain_if_ready:2991 > Lock.acquire

#2129 removes the lock bug itself. This PR is the defense in depth: a hot path shared by every request must not be able to park the fleet behind one detached generation, whatever keeps its lock busy.

What

• _retire_http_bridge_after_drain_if_ready(session, *, lock_wait_timeout_seconds=None): with a bound, the pending_lock acquire goes through scheduler_for(self).wait_for(...); on timeout it logs a warning naming the (hashed) session key, leaves the session tracked and its state untouched, and returns False. None keeps the unbounded wait for lifecycle owners (drain, close, cooldown-suppression retirement), so retirement decisions stay authoritative there.
• The per-request sweep passes a fixed 5 s bound (_HTTP_BRIDGE_DETACHED_RETIRE_LOCK_WAIT_SECONDS, a hardcoded constant, no new setting). A skipped session is reconsidered by the next request's sweep and by its own drain/close paths.
• Regressions (tests/unit/test_http_bridge_idle_leases.py): sweep against a permanently held detached lock returns within the bound, closes nothing, and leaves the lock owned by its holder with no stranded waiter; a free lock still retires; a lifecycle owner without the bound still waits and then retires.
• OpenSpec change bound-detached-retire-sweep-lock-wait (responses-api-compat delta).

Validation

• pytest tests/unit (full suite locally; only the three pre-existing main environment failures deselected — two test_metrics cases needing prometheus_client absent, and the file_account_pins sqlite case)
• ruff check / ruff format --check / ty check / check_proxy_architecture.py / check_cancellation_safety.py / check_proxy_timing_seams.py
• openspec validate bound-detached-retire-sweep-lock-wait --strict

Related to #2029
Related to #2129

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Prevented requests from stalling when a detached HTTP session’s lock remains held.
  • Retirement sweeps now wait up to five seconds, log a warning on timeout, and retry the session later.
  • Sessions with available locks continue to close normally.
  • Other cleanup paths retain their existing waiting behavior.
• Tests
  • Added coverage for locked and available sessions, including lifecycle cleanup behavior.

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• tests/unit/test_http_bridge_idle_leases.py

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• tests/unit/test_http_bridge_idle_leases.py

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📝 Walkthrough

Walkthrough

The HTTP bridge now bounds request-triggered detached-session retirement lock waits to five seconds. Timed-out sessions remain unchanged and are retried later. Lifecycle-owned retirement keeps unbounded lock waits. Tests cover both paths.

Changes

Detached-session retirement lock wait

Layer / File(s)	Summary
Retirement timeout behavior app/modules/proxy/_service/http_bridge/protocol.py, app/modules/proxy/_service/http_bridge/request_submit.py, openspec/changes/bound-detached-retire-sweep-lock-wait/proposal.md, openspec/changes/bound-detached-retire-sweep-lock-wait/specs/responses-api-compat/spec.md	The retirement method accepts an optional keyword-only timeout. Timed-out lock acquisition logs a warning and returns without changing the session. Calls without a timeout remain unbounded.
Request sweep timeout wiring app/modules/proxy/_service/http_bridge/helpers.py, openspec/changes/bound-detached-retire-sweep-lock-wait/tasks.md, openspec/changes/bound-detached-retire-sweep-lock-wait/.openspec.yaml	The per-request detached-session sweep passes a fixed five-second timeout to retirement checks. OpenSpec metadata records the change.
Retirement behavior validation tests/unit/test_http_bridge_idle_leases.py, tests/unit/test_proxy_http_bridge.py	Tests cover held and free locks, unbounded lifecycle retirement, elapsed timeout behavior, and the updated timeout argument.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 42481

Request-triggered detached-session cleanup now limits lock waits to five seconds while preserving unbounded lifecycle retirement. Lock contention defers cleanup rather than blocking requests, with no concrete merge-blocking risk identified.

Sequence Diagram(s)

sequenceDiagram
  participant Request
  participant HTTPBridgeSweep
  participant HTTPBridgeRetirement
  participant pending_lock
  Request->>HTTPBridgeSweep: trigger detached-session cleanup
  HTTPBridgeSweep->>HTTPBridgeRetirement: retire with 5-second timeout
  HTTPBridgeRetirement->>pending_lock: wait for lock
  pending_lock-->>HTTPBridgeRetirement: acquired or timeout
  HTTPBridgeRetirement-->>HTTPBridgeSweep: retire session or skip

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🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 37.50% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 16 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: bounding the pending_lock wait during the detached-session retirement sweep.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Commit unit tests in branch fix/bounded-detached-retire-sweep

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Actionable comments posted: 1

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Inline comments:
In `@tests/unit/test_http_bridge_idle_leases.py`:
- Line 1232: Update the timeout assertion in the idle-lease test around the
timeout argument so its deadline is close to the configured 0.05-second lock
wait while allowing a small scheduling margin; do not retain the broad
one-second timeout that permits substantially longer waits.

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Configuration used: defaults

Review profile: CHILL

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📥 Commits

Reviewing files that changed from the base of the PR and between 6bba5ce and 29cbbb7.

📒 Files selected for processing (9)

• app/modules/proxy/_service/http_bridge/helpers.py
• app/modules/proxy/_service/http_bridge/protocol.py
• app/modules/proxy/_service/http_bridge/request_submit.py
• openspec/changes/bound-detached-retire-sweep-lock-wait/.openspec.yaml
• openspec/changes/bound-detached-retire-sweep-lock-wait/proposal.md
• openspec/changes/bound-detached-retire-sweep-lock-wait/specs/responses-api-compat/spec.md
• openspec/changes/bound-detached-retire-sweep-lock-wait/tasks.md
• tests/unit/test_http_bridge_idle_leases.py
• tests/unit/test_proxy_http_bridge.py

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