fix(core): stop SSEStreamSubscription retrying permanent 4xx forever

Author: ericallam

packages/core/src/v3/apiClient/runStream.ts

@@ -233,8 +233,10 @@ export class SSEStreamSubscription implements StreamSubscription {
       // reset the timer naturally.
       stallTimeoutMs?: number;
       // HTTP statuses that should NOT be retried — fail the stream
-      // permanently. `404` (stream gone) and `410` (session closed)
-      // are sensible defaults; tune per-caller for other 4xx.
+      // permanently. Defaults cover the permanent client-error set:
+      // `400` (bad request), `404` (stream gone), `409` (conflict),
+      // `410` (session closed), `422` (unprocessable). Tune per-caller
+      // for other 4xx.
       nonRetryableStatuses?: readonly number[];
       // Optional fetch override. Used by transports that need to route
       // the SSE connect through a custom path (proxy, custom headers,