fix(usage): explain unavailable provider limits

[pseudoseed]

The Limits view could show a failed usage read for a Codex account that was never signed in, and describe unavailable Claude token or cloud-backend limits as a missing subscription.

Omit the redundant Codex warning while preserving errors for signed-in accounts. Use the same Claude probe’s account metadata to explain unavailable limits, without changing any returned usage windows or authentication state. Existing shared notice rendering carries the messages to web, desktop, and mobile over local and remote connections; other providers are unchanged.

Validation: 64 focused provider and usage tests passed, server typecheck passed, targeted lint/formatting passed. Includes regression coverage for both Claude probe paths, token and cloud-backend notices, signed-out Codex, API-key accounts, and real usage-read failures.

Model: GPT-6 Astra. Harness: Codex.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.9 KiB	14.0 KiB	+100 B (+0.7%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.3 KiB	7.3 KiB	+7 B (+0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.6 KiB	6.7 KiB	+93 B (+1.4%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.5 KiB	58.3 KiB	+822 B (+1.4%)	66.4 KiB	✅
Codex	Live turn messages	8	8	0 (0.0%)	21	✅
Claude	Total thread wire	14.0 KiB	14.0 KiB	−48 B (−0.3%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.3 KiB	7.3 KiB	−7 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.8 KiB	6.7 KiB	−41 B (−0.6%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	59.2 KiB	59.1 KiB	−44 B (−0.1%)	66.4 KiB	✅
Claude	Live turn messages	9	8	−1 (−11.1%)	21	✅

Baseline: 7499db0 · PR result: 60b3397 · 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: 116.2 KiB
• Claude decoded thread snapshot: 116.9 KiB

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