[oliverlaz]

Summary

When the API returns an error, ApiClient parses the JSON body (APIError) but only copies code and message into the thrown StreamError. Everything else the server sends is lost, most notably exception_fields, which names the field that caused a validation or conflict error (for example last_message_id on a stale channel rewind, or the fork target on fork_target_exists).

This adds an optional apiError property to StreamError, holding the parsed error body as returned by the API (exception_fields, details, more_info, status_code, unrecoverable, ...).

• StreamError gains a fifth, optional constructor argument apiError?: APIError. Existing call sites and instanceof checks are unaffected.
• ApiClient.sendRequest passes the parsed body when the error response is JSON. apiError stays undefined for network failures, timeouts, and non-JSON error bodies.

Why

The Chat QA suite (GetStream/chat#16042) asserts exception_fields on rewind and fork conflict errors. It moved to node-sdk 0.9.0 and can no longer reach them, so those assertions currently only check the status, code and message.

Tests

New __tests__/integration/api-error.test.ts, mocking fetch like network-error.test.ts:

• a 409 with a JSON error body: apiError equals the body, including exception_fields
• a 502 with an HTML body: apiError is undefined and the message stays Stream error: 502 - Bad Gateway

yarn tsc --noEmit, ESLint, Prettier and yarn build pass; the emitted StreamError declaration includes apiError.