feat(assistant): trip assistant chat with your own AI connection

Adds an in-app assistant that reads and plans the open trip. Users connect
their own provider (Sign in with ChatGPT, or an Anthropic, OpenAI, Gemini or
OpenRouter key) or use the one the admin set up, including a custom
OpenAI-compatible server. It is an addon and only shows while a connection
is usable.

The chat runs on the existing MCP tools, pinned to the trip. Every change is
held as a change card the user applies or discards, and applied changes can
be undone. On the desktop it is a floating window that can be moved and
resized; on the phone it is fullscreen. Search results show as place cards
that can go onto a day, weather lookups as a strip, proposed places as
ghost markers on the map with a before/after switch, and an answer can be
shared into the trip chat. Booking files can be dropped in and are read
into change cards.

client/src/api/assistant.test.ts

@@ -0,0 +1,133 @@
+/**
+ * FE-AI-API-001 to FE-AI-API-007
+ *
+ * The two streaming calls bypass axios, so they carry by hand what the axios
+ * instance would add (the cookie, the socket id) and turn a refusal before the
+ * stream into a typed error the chat can name. The refusal's code comes from
+ * the body when the server names one, and from the status otherwise.
+ */
+import type { AssistantChatRequest } from '@trek/shared';
+import { http, HttpResponse } from 'msw';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { server } from '../../tests/helpers/msw/server';
+import { assistantApi, AssistantRequestError } from './assistant';
+import { getSocketId } from './websocket';
+
+const BODY: AssistantChatRequest = { locale: 'en', timeZone: 'Europe/Berlin', threadId: null, text: 'Hi' };
+
+function streamResponse(text: string): Response {
+  const bytes = new TextEncoder().encode(text);
+  let sent = false;
+  return {
+    ok: true,
+    status: 200,
+    body: {
+      getReader: () => ({
+        read: async () => {
+          if (sent) return { done: true, value: undefined };
+          sent = true;
+          return { done: false, value: bytes };
+        },
+        cancel: async () => {},
+      }),
+    },
+  } as unknown as Response;
+}
+
+function refusal(status: number, body: unknown): Response {
+  return {
+    ok: false,
+    status,
+    body: null,
+    json: async () => {
+      if (body === undefined) throw new SyntaxError('not json');
+      return body;
+    },
+  } as unknown as Response;
+}
+
+async function refusedWith(res: Response) {
+  vi.spyOn(globalThis, 'fetch').mockResolvedValueOnce(res);
+  try {
+    await assistantApi.chat(4, BODY, new AbortController().signal);
+  } catch (err) {
+    return err;
+  }
+  throw new Error('expected a refusal');
+}
+
+afterEach(() => vi.restoreAllMocks());
+
+describe('assistantApi streams', () => {
+  it('FE-AI-API-001: posts the message as JSON with the cookie and the socket id, and yields the chunks', async () => {
+    vi.mocked(getSocketId).mockReturnValueOnce('sock-1');
+    const fetchSpy = vi
+      .spyOn(globalThis, 'fetch')
+      .mockResolvedValueOnce(streamResponse('data: {"type":"start","messageId":"m1"}\n\ndata: [DONE]\n\n'));
+    const signal = new AbortController().signal;
+
+    const chunks: unknown[] = [];
+    for await (const chunk of await assistantApi.chat(4, BODY, signal)) chunks.push(chunk);
+
+    expect(chunks).toEqual([{ type: 'start', messageId: 'm1' }]);
+    const [url, init] = fetchSpy.mock.calls[0] ?? [];
+    expect(url).toBe('/api/trips/4/assistant/chat');
+    expect(init).toMatchObject({ method: 'POST', credentials: 'include', signal, body: JSON.stringify(BODY) });
+    expect(init?.headers).toMatchObject({
+      'content-type': 'application/json',
+      accept: 'text/event-stream',
+      'X-Socket-Id': 'sock-1',
+    });
+  });
+
+  it('FE-AI-API-002: sends decisions to the thread they belong to', async () => {
+    const fetchSpy = vi.spyOn(globalThis, 'fetch').mockResolvedValueOnce(streamResponse('data: [DONE]\n\n'));
+    const body = { locale: 'de', timeZone: 'UTC', decisions: [{ toolCallId: 'c1', approved: true }] };
+    await assistantApi.decide(4, 7, body, new AbortController().signal);
+    expect(fetchSpy.mock.calls[0]?.[0]).toBe('/api/trips/4/assistant/threads/7/decisions');
+  });
+
+  it('FE-AI-API-003: a refusal names the code the body gives', async () => {
+    const err = await refusedWith(refusal(429, { error: 'Daily limit reached', code: 'daily_limit' }));
+    expect(err).toBeInstanceOf(AssistantRequestError);
+    expect(err).toMatchObject({ code: 'daily_limit', status: 429 });
+  });
+
+  it('FE-AI-API-004: without a known code the status decides', async () => {
+    expect(await refusedWith(refusal(429, { error: 'slow down' }))).toMatchObject({ code: 'too_many_requests' });
+    expect(await refusedWith(refusal(409, { error: 'x', code: 'conflict' }))).toMatchObject({ code: 'busy' });
+    expect(await refusedWith(refusal(502, undefined))).toMatchObject({ code: 'provider_unavailable' });
+    expect(await refusedWith(refusal(500, { error: 'boom' }))).toMatchObject({ code: 'generic' });
+  });
+
+  it('FE-AI-API-005: an accepted request without a body is a generic failure, not a silent empty answer', async () => {
+    const err = await refusedWith({ ok: true, status: 200, body: null } as unknown as Response);
+    expect(err).toMatchObject({ code: 'generic', status: 200 });
+  });
+});
+
+describe('assistantApi JSON calls', () => {
+  it('FE-AI-API-006: undo posts an empty JSON body to the escaped tool call id', async () => {
+    let seen: { path: string; body: unknown } | null = null;
+    server.use(
+      http.post('/api/trips/4/assistant/tool-calls/:id/undo', async ({ request, params }) => {
+        seen = { path: String(params.id), body: await request.json() };
+        return HttpResponse.json({ undone: true });
+      })
+    );
+    await expect(assistantApi.undo(4, 'a/b')).resolves.toEqual({ undone: true });
+    expect(seen).toEqual({ path: 'a/b', body: {} });
+  });
+
+  it('FE-AI-API-007: stop posts an empty JSON body', async () => {
+    let body: unknown = null;
+    server.use(
+      http.post('/api/trips/4/assistant/stop', async ({ request }) => {
+        body = await request.json();
+        return HttpResponse.json({ success: true });
+      })
+    );
+    await expect(assistantApi.stop(4)).resolves.toEqual({ success: true });
+    expect(body).toEqual({});
+  });
+});