Summary

Anthropic's rate limit error "You've hit your limit · resets 5pm (UTC)" is not recognized as retryable by either the model-fallback or runtime-fallback error classifiers, preventing automatic fallback to alternative providers.

Changes

• Add "hit your limit" and "hit the limit" to RETRYABLE_MESSAGE_PATTERNS in src/shared/model-error-classifier.ts (used by model-fallback)
• Add /hit.{0,10}(?:your|the)?.{0,5}limit/i regex to RETRYABLE_ERROR_PATTERNS in src/hooks/runtime-fallback/constants.ts (used by runtime-fallback)

Context

When Anthropic returns this error, the log shows:

[background-agent] Session error - no retry: {
  "errorName":"APIError",
  "errorMessage":"Claude Code returned an error result: You've hit your limit · resets 5pm (UTC)",
  "hasFallbackChain":true,
  "canRetry":false
}

The fallback chain exists (hasFallbackChain: true) but canRetry is false because neither classifier matches the "hit your limit" phrasing. The existing patterns cover "over limit", "rate limit", and "rate_limit" but miss this specific Anthropic wording.

Testing

• bun run typecheck passes
• bun run build passes

Summary by cubic

Recognize Anthropic “You’ve hit your limit”, Gemini “spending cap”, and generic “usage limit” messages so cross‑provider fallback kicks in reliably. Split retry logic so quota/billing/usage STOP errors trigger fallback, while same‑provider retries stay unchanged.

• Bug Fixes
  • Add “hit your/the limit” to RETRYABLE_MESSAGE_PATTERNS; add runtime regex for hit.*limit, usage.*limit, and spending.*cap.
  • Add isStopModelError; update shouldRetryError to return true for retryable and STOP errors; move “spending cap” and “usage limit has been reached” to STOP patterns.
  • Expand tests for new patterns, STOP vs retryable behavior (isStopModelError, isRetryableModelError), and fallback provider selection.

^{Written for commit 7175c57. Summary will update on new commits.}