X_MCP_RATE_LIMITED

the caller has spent its allowance for this request's class

more than rateLimits.read or rateLimits.write requests in one minute from one actor, metered by mcpHttpRoute after the body is parsed (the class comes out of the body) and before the tool runs. 429 with Retry-After; the bucket key names the actor and never reaches the caller. It has its own code rather than reusing X_RATE_LIMITED because the KNOB differs — the HTTP pipeline's buckets do not govern this route, so raising them would run and change nothing

wait out the Retry-After, or raise it where the route is built: mcpHttpRoute({ rateLimits: { read: <n>, write: <n> } }), or defineAppMcp({ rateLimits }). Behind N replicas pass rateLimitStore: postgresRateLimitStore({ executor }) too, or each enforces the full allowance on its own