Add canvas artifact RPC foundation for A2UI

src/gateway/server.test.ts

@@ -234,6 +234,46 @@ describe('GatewayServer integration', () => {
     expect(methods).toContain('sessions.create');
     expect(methods).toContain('tools.list');
     expect(methods).toContain('tools.invoke');
+    expect(methods).toContain('canvas.put');
+    expect(methods).toContain('canvas.list');
+  });
+
+  it('supports canvas artifact lifecycle via gateway RPC', async () => {
+    if (!LISTEN_ALLOWED) {
+      return;
+    }
+    const ws = await createClient();
+    try {
+      const put = await sendAndReceive(ws, {
+        id: 31,
+        method: 'canvas.put',
+        params: {
+          sessionId: 'ws:test-canvas',
+          artifactId: 'a1',
+          type: 'note',
+          content: { text: 'draft' },
+        },
+      });
+      expect((put as GatewayResponse).id).toBe(31);
+
+      const list = await sendAndReceive(ws, {
+        id: 32,
+        method: 'canvas.list',
+        params: { sessionId: 'ws:test-canvas' },
+      });
+      const artifacts = ((list as GatewayResponse).result as { artifacts: Array<{ id: string }> }).artifacts;
+      expect(artifacts).toHaveLength(1);
+      expect(artifacts[0]?.id).toBe('a1');
+
+      const clear = await sendAndReceive(ws, {
+        id: 33,
+        method: 'canvas.clear',
+        params: { sessionId: 'ws:test-canvas' },
+      });
+      expect(((clear as GatewayResponse).result as { cleared: number }).cleared).toBe(1);
+    } finally {
+      ws.close();
+    }
   });
 
   // ── HTTP static file serving tests ────────────────────────────