Error: discord block reply failed: Error: You are being rate limited.

Problem:

• Messages dropped silently when Discord returns 429
• No retry logic in place

Need:

• Detect 429 rate limit responses
• Read retry-after header from Discord
• Implement exponential backoff

Affected: src/auto-reply/reply/agent-runner.ts (block reply handling), Discord message sending

Workaround: Reduce heartbeat frequency, consolidate responses

Context:
Carbon's RequestClient has queueRequests: true by default, but the rate limit error still propagates up. The onBlockReply callback throws and the error is only logged, not retried:

.catch((err) => {
  logVerbose(`block reply delivery failed: ${String(err)}`);
});