Limits

Validate these limits before sending a request.

Messages

Limit	Value
Parts per Message	100
Public URL media parts per Message	40
Text part	10,000 UTF-16 code units
Link URL	2,048 characters
Idempotency key	255 characters

Limit	Value
Webhook response timeout	10 seconds
Webhook attempts	10
WebSocket active connections	Multiple per agent, sharing one checkpoint
WebSocket in-flight window	Returned in `ready.max_in_flight`

Relay returns 400, 413, 415, 422, or 429 depending on the rejected boundary. Use the numeric error code for program logic.