fix(server): Claude threads continue after an account hits its limit

[bk-agent-01]

Problem

When a Claude account reached its usage limit, the chat stopped with "Claude usage limit reached". The account rotation code is supposed to move an Auto thread to the next account and send "Continue". It never ran.

The cause: the rotation listened only for account.rate-limits.updated. When Claude rejects a request, its rate_limit_event has no top-level utilization (only unifiedWindows.<window>.utilization), so claudeRateLimitEventToUpdate drops it and that event never fires. Model-scoped rejections (seven_day_opus, …) never produce it at all.

Evidence from bkt3: about 20 rejected events in the provider logs since 2026-10-03, for example thread aee72ad8… at 2026-10-05 20:28 UTC. Each produced only the usage-limit runtime.warning. The server log has 55 claude.account.placed lines since the last restart and zero claude.account.hard-limit lines.

Fix

1. claudeHardLimitRotation.expbkt3.ts: trigger on the adapter's usage-limit runtime.warning. It carries Claude's rate_limit_info as its detail, covers every limit type, and fires only when the rejection blocks the turn. A rejection that overage absorbs stays quiet, as it does today. No upstream file changes.
2. ClaudeAccountsService.ts: when the limit resets in 5 minutes or less, an Auto thread does not move. The session stops, and a notice says when the thread will continue. One minute after the reset, the thread gets a "Continue" turn on the same account.
   • A message accepted for the thread, an account-mode change, or a thread delete cancels the wait.
   • If Claude still refuses after the reset time, the thread moves instead of waiting again.
   • The timer is in memory, so a server restart during the wait leaves only the notice.

Pinned threads are not changed: they still get a notice only.

Tests

• claudeHardLimitRotation.expbkt3.test.ts: the warning triggers rotation for 5-hour and Opus limits. A rejection that overage absorbs, other warnings, and allowed events do not trigger it.
• ClaudeAccountsService.test.ts: the thread waits and then continues on the same account; a later refusal with the old reset moves it; an accepted message, a turn start, or a mode change cancels the wait; a reset more than 5 minutes away moves the thread.
• Locally: 84 tests in the 3 related files pass, the server typecheck passes, lint is clean on the changed files, and the fork-marker check passes against upstream main.

Known follow-up

If the switcher's cached usage still shows 100% after the reset, the continue turn lands on another account. The thread still continues, but it loses the cache the wait tried to keep.

Deploy note

Merging to bkmain restarts bkt3 and stops every running session on it. This PR targets bkmain directly, at the operator's request (no expbkt3 stage).

Opus 5.5 in Claude Code.

🤖 Generated with Claude Code

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	13.7 KiB	—	15.1 KiB	✅
Codex	Thread snapshot wire	—	7.2 KiB	—	7.8 KiB	✅
Codex	Live turn WebSocket wire	—	6.5 KiB	—	7.8 KiB	✅
Codex	Live turn WebSocket decoded	—	56.3 KiB	—	66.4 KiB	✅
Codex	Live turn messages	—	9	—	21	✅
Claude	Total thread wire	—	13.7 KiB	—	15.1 KiB	✅
Claude	Thread snapshot wire	—	7.2 KiB	—	7.8 KiB	✅
Claude	Live turn WebSocket wire	—	6.5 KiB	—	7.8 KiB	✅
Claude	Live turn WebSocket decoded	—	57.1 KiB	—	66.4 KiB	✅
Claude	Live turn messages	—	9	—	21	✅

Baseline: unavailable · PR result: f3f2671 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 114.6 KiB
• Claude decoded thread snapshot: 115.3 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.