Fix: Improve Sentry error reporting for API failures

lib/__tests__/throwIfNotOk.test.ts

@@ -0,0 +1,58 @@
+/// <reference types="jest" />
+
+import { throwIfNotOk } from '@/lib/api';
+
+/**
+ * Regression guard for SOLID-W3: ensureWebhookSubscription (and all other
+ * fetch calls in lib/api.ts) previously threw the raw Response object when the
+ * server returned a non-2xx status. TanStack Mutation's onError passed it
+ * directly to Sentry.captureException, which serialised the Response keys
+ * (_bodyBlob, _bodyInit, ok, status…) as the exception title rather than a
+ * human-readable message.
+ *
+ * throwIfNotOk ensures every failed fetch produces a proper Error instance.
+ */
+describe('throwIfNotOk', () => {
+  const makeResponse = (status: number, statusText: string, ok: boolean): Response =>
+    ({
+      ok,
+      status,
+      statusText,
+      url: 'https://api.example.com/test',
+    }) as unknown as Response;
+
+  it('does nothing when the response is OK', () => {
+    const response = makeResponse(200, 'OK', true);
+    expect(() => throwIfNotOk(response)).not.toThrow();
+  });
+
+  it('throws an Error instance (not the Response object) on a non-OK response', () => {
+    const response = makeResponse(401, 'Unauthorized', false);
+    expect(() => throwIfNotOk(response)).toThrow(Error);
+  });
+
+  it('includes the HTTP status code in the error message', () => {
+    const response = makeResponse(401, 'Unauthorized', false);
+    expect(() => throwIfNotOk(response)).toThrow('401');
+  });
+
+  it('includes the status text in the error message', () => {
+    const response = makeResponse(503, 'Service Unavailable', false);
+    expect(() => throwIfNotOk(response)).toThrow('Service Unavailable');
+  });
+
+  it('includes the URL in the error message', () => {
+    const response = makeResponse(500, 'Internal Server Error', false);
+    expect(() => throwIfNotOk(response)).toThrow('https://api.example.com/test');
+  });
+
+  it('throws for 4xx responses', () => {
+    const response = makeResponse(403, 'Forbidden', false);
+    expect(() => throwIfNotOk(response)).toThrow(Error);
+  });
+
+  it('throws for 5xx responses', () => {
+    const response = makeResponse(500, 'Internal Server Error', false);
+    expect(() => throwIfNotOk(response)).toThrow(Error);
+  });
+});