feat: implement PI core chat timeline

tests/unit/host-api-proxy.test.ts

@@ -113,4 +113,48 @@ describe('Host API IPC proxy', () => {
       data: { status: 200, ok: true, json: { success: true, transport: 'test' }, transport: 'dispatcher' },
     });
   });
+
+  it('keeps attachment upload bytes raw and returns image bytes through IPC', async () => {
+    const fetchMock = vi.fn()
+      .mockResolvedValueOnce(new Response(
+        JSON.stringify({ attachmentId: 'attachment-1', mime: 'image/png', byteLength: 4 }),
+        { status: 201, headers: { 'content-type': 'application/json' } },
+      ))
+      .mockResolvedValueOnce(new Response(
+        new Uint8Array([1, 2, 3, 4]),
+        { status: 200, headers: { 'content-type': 'image/png' } },
+      ));
+    vi.stubGlobal('fetch', fetchMock);
+
+    const { registerHostApiProxyHandlers } = await import('../../electron/main/ipc/host-api-proxy');
+    registerHostApiProxyHandlers({} as never);
+    const fetchHandler = handleMock.mock.calls.find(([channel]) => channel === 'hostapi:fetch')?.[1];
+
+    const upload = await fetchHandler(undefined, {
+      path: '/api/coding/attachments',
+      method: 'POST',
+      headers: { 'Content-Type': 'image/png' },
+      body: new Uint8Array([1, 2, 3, 4]).buffer,
+    });
+    const [, uploadInit] = fetchMock.mock.calls[0] as [string, RequestInit];
+    expect(Array.from(uploadInit.body as Uint8Array)).toEqual([1, 2, 3, 4]);
+    expect(new Headers(uploadInit.headers).get('content-type')).toBe('image/png');
+    expect(upload).toMatchObject({
+      ok: true,
+      data: { status: 201, json: { attachmentId: 'attachment-1' } },
+    });
+
+    const preview = await fetchHandler(undefined, {
+      path: '/api/coding/attachments/attachment-1/content',
+      method: 'GET',
+    });
+    expect(preview).toMatchObject({
+      ok: true,
+      data: {
+        status: 200,
+        contentType: 'image/png',
+        bytes: new Uint8Array([1, 2, 3, 4]),
+      },
+    });
+  });
 });