fix(app): emit title and omit absent outputSchema in tools/list

Author: ochafik

src/app-bridge.test.ts

@@ -1287,6 +1287,40 @@ describe("App <-> AppBridge integration", () => {
         expect(result.tools.map((t) => t.name)).toContain("tool3");
       });
 
+      it("emits core MCP Tool fields (title, outputSchema only when provided)", async () => {
+        const appCapabilities = { tools: { listChanged: true } };
+        app = new App(testAppInfo, appCapabilities, { autoResize: false });
+
+        app.registerTool(
+          "with-output",
+          {
+            title: "With Output",
+            description: "has structured output",
+            outputSchema: z.object({ ok: z.boolean() }),
+          },
+          async () => ({
+            content: [],
+            structuredContent: { ok: true },
+          }),
+        );
+        app.registerTool(
+          "no-output",
+          { description: "no structured output" },
+          async () => ({ content: [] }),
+        );
+
+        await app.connect(appTransport);
+        const result = await bridge.listTools({});
+        const byName = Object.fromEntries(result.tools.map((t) => [t.name, t]));
+
+        expect(byName["with-output"].title).toBe("With Output");
+        expect(byName["with-output"].inputSchema).toBeDefined();
+        expect(byName["with-output"].outputSchema).toBeDefined();
+        // outputSchema is optional in core MCP — omitted when not declared
+        expect(byName["no-output"]).not.toHaveProperty("outputSchema");
+        expect(byName["no-output"].inputSchema).toBeDefined();
+      });
+
       it("returns empty list when no tools registered", async () => {
         const appCapabilities = { tools: { listChanged: true } };
         app = new App(testAppInfo, appCapabilities, { autoResize: false });

src/app.ts

@@ -424,20 +424,22 @@ export class App extends ProtocolWithEvents<
         .map(([name, tool]) => {
           const result: Tool = {
             name,
+            title: tool.title,
             description: tool.description,
             inputSchema: (tool.inputSchema
               ? z.toJSONSchema(tool.inputSchema as ZodSchema)
               : {
                   type: "object" as const,
                   properties: {},
                 }) as Tool["inputSchema"],
-            outputSchema: (tool.outputSchema
-              ? z.toJSONSchema(tool.outputSchema as ZodSchema)
-              : {
-                  type: "object" as const,
-                  properties: {},
-                }) as Tool["outputSchema"],
           };
+          // outputSchema is optional in core MCP — only emit when the app
+          // provided one, otherwise hosts would assume structuredContent.
+          if (tool.outputSchema) {
+            result.outputSchema = z.toJSONSchema(
+              tool.outputSchema as ZodSchema,
+            ) as Tool["outputSchema"];
+          }
           if (tool.annotations) {
             result.annotations = tool.annotations;
           }