OpenRouter guide: fixing OpenAI and Claude 429 rate limit errors

OpenRouter published a guide on handling 429 Too Many Requests errors from OpenAI, Anthropic and its own API, testing three fixes on a 60-prompt batch. The OpenAI Python SDK's default retries left 23 of 60 requests failed in 12 seconds, while a retry that waits for Retry-After or X-RateLimit-Reset completed all 60 in 89 to 92 seconds in Python and 106 to 218 seconds in TypeScript. A models fallback finished all 60 in 13 seconds for $0.000066, and with provider failover on, all 150 pinned-provider requests succeeded where up to 32 failed with fallbacks off.