Retry and recovery

• 429. Honor Retry-After. The hosted API allows about 60 ingestion requests and 120 runtime requests per 60 seconds.
• 413. Batch max 256 KiB, event max 32 KiB, 100 events. The SDK shrinks the batch.
• 401 / 403. Export suspends. Fix the key, then resumeExport().
• 5xx. Retry the same eventId. Server dedup makes that safe.

retryable: false means drop the event. A new id would store a bad payload twice if the first one had actually landed.