fix(matrix): allow attachment-only outbound messages

src/channels/matrix/adapter.test.ts

@@ -146,6 +146,36 @@ describe('MatrixAdapter', () => {
     });
   });
 
+  it('uploads binary attachments when outbound text is empty', async () => {
+    mockFetch.mockImplementation(async (url: string, init?: RequestInit) => {
+      if (url.endsWith('/_matrix/client/v3/account/whoami')) {
+        return jsonResponse({ user_id: '@flynn:example.org' });
+      }
+      if (url.includes('/account_data/m.direct')) {
+        return jsonResponse({});
+      }
+      if (url.includes('/_matrix/client/v3/sync')) {
+        return new Promise<Response>(() => {});
+      }
+      if (init?.method === 'POST' && url.includes('/_matrix/client/v3/upload')) {
+        return jsonResponse({ content_uri: 'mxc://example.org/media123' });
+      }
+      if (init?.method === 'PUT' && url.includes('/send/m.room.message/')) {
+        const body = JSON.parse(String(init?.body ?? '{}'));
+        expect(body.msgtype).toBe('m.image');
+        expect(body.url).toBe('mxc://example.org/media123');
+        return jsonResponse({ event_id: '$media2' });
+      }
+      throw new Error(`Unexpected fetch URL: ${url}`);
+    });
+
+    await adapter.connect();
+    await adapter.send('!room1:example.org', {
+      text: '  ',
+      attachments: [{ mimeType: 'image/png', data: 'aGVsbG8=', filename: 'image.png' }],
+    });
+  });
+
   it('inbound message requires mention in non-DM rooms', async () => {
     const handler = vi.fn();
     adapter.onMessage(handler);