Google's quota API can report remaining quota while generation endpoints
keep returning 429 (sprint/weekly dual-pool mismatch). handleAntigravityQuotaError
trusted remainingPercentage > 0 as healthy and returned null, causing 429 retry
loops across multi-account pools.
Add a strike-based circuit breaker to the optimistic and unavailable quota paths:
- After 3 strikes (429/409) within 60s for the same connection+model, cache-block
that pair for 15 minutes by synthesizing an entry in the shared RAM quota cache.
- Re-assert active strike blocks across refreshes so optimistic readings cannot
resurrect a broken pair prematurely.
- Reset strikes and clear synthesized cache entry upon successful request.
- Keep exact-resetAt handling for genuine 0% exhausted readings.
Closes#3681
On a 409/429 from Antigravity, fetch live quota to learn the exact
per-model resetAt instead of guessing a backoff, then skip only the
exhausted account/model pair until that time.
- antigravityQuota.js: in-memory quota cache, coalesced concurrent
refreshes, 30s throttle per connection (applied to failures too),
keeps known cache when upstream returns 401/403 error payloads
- auth.js: pre-filter exhausted account/model pairs; report the
earliest quota reset when every account is blocked; skip the
30-minute cooldown cap so the upstream resetAt is not truncated
- chat.js: antigravity 409/429 falls back on the RAM cache only, no
persistent modelLock_* for this path
- Logs identify accounts by id prefix, never email or name
Closes#3561
