feat: implement PI core chat timeline

tests/unit/host-api.test.ts

@@ -65,6 +65,33 @@ describe('host-api', () => {
     await expect(hostApiFetch('/api/test')).resolves.toBeUndefined();
   });
 
+  it('returns authenticated binary IPC data without JSON or browser fallback', async () => {
+    const bytes = new Uint8Array([9, 8, 7]);
+    invokeIpcMock.mockResolvedValueOnce({
+      ok: true,
+      data: {
+        status: 200,
+        ok: true,
+        bytes,
+        contentType: 'image/webp',
+      },
+    });
+    const fetchMock = vi.fn();
+    vi.stubGlobal('fetch', fetchMock);
+
+    const { hostApiFetchBytes } = await import('@/lib/host-api');
+
+    await expect(hostApiFetchBytes('/api/coding/attachments/attachment-1/content'))
+      .resolves.toEqual({ bytes, contentType: 'image/webp' });
+    expect(invokeIpcMock).toHaveBeenCalledWith('hostapi:fetch', {
+      path: '/api/coding/attachments/attachment-1/content',
+      method: 'GET',
+      headers: { Accept: 'application/octet-stream' },
+      body: null,
+    });
+    expect(fetchMock).not.toHaveBeenCalled();
+  });
+
   it('supports legacy proxy envelope response', async () => {
     invokeIpcMock.mockResolvedValueOnce({
       success: true,