- Classified usage-limit gateway responses as `429 rate_limit_error` in auth handling paths.
- Aligned auth-gateway and pi-native key retrieval with derived `sessionId` for `getApiKey` lookups.
- Handled usage-limit auth failures by rotating credentials with retry hints and returning undefined when none available.
- Replaced stream auth checks with retryable-upstream logic for 401 and usage-limit errors before content.
- Expanded `extractRetryHint` parsing for `~`, `sec`, `ms`, and minute/hour units.
- Added coverage for classifyGatewayError, retry-hint parsing variants, and stream-auth retry edge cases.
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