feat(core): simplify subagent success UI and improve early termination display (#21917)

packages/core/src/agents/local-invocation.test.ts

@@ -207,8 +207,24 @@ describe('LocalSubagentInvocation', () => {
           ),
         },
       ]);
-      expect(result.returnDisplay).toContain('Result:\nAnalysis complete.');
+      expect(result.returnDisplay).toBe('Analysis complete.');
-      expect(result.returnDisplay).toContain('Termination Reason:\n GOAL');
+      expect(result.returnDisplay).not.toContain('Termination Reason');
+    });
+
+    it('should show detailed UI for non-goal terminations (e.g., TIMEOUT)', async () => {
+      const mockOutput = {
+        result: 'Partial progress...',
+        terminate_reason: AgentTerminateMode.TIMEOUT,
+      };
+      mockExecutorInstance.run.mockResolvedValue(mockOutput);
+
+      const result = await invocation.execute(signal, updateOutput);
+
+      expect(result.returnDisplay).toContain(
+        '### Subagent MockAgent Finished Early',
+      );
+      expect(result.returnDisplay).toContain('**Termination Reason:** TIMEOUT');
+      expect(result.returnDisplay).toContain('Partial progress...');
     });
 
     it('should stream THOUGHT_CHUNK activities from the executor', async () => {
@@ -296,7 +312,7 @@ describe('LocalSubagentInvocation', () => {
       // Execute without the optional callback
       const result = await invocation.execute(signal);
       expect(result.error).toBeUndefined();
-      expect(result.returnDisplay).toContain('Result:\nDone');
+      expect(result.returnDisplay).toBe('Done');
     });
 
     it('should handle executor run failure', async () => {

packages/core/src/agents/local-invocation.ts

@@ -253,12 +253,15 @@ Termination Reason: ${output.terminate_reason}
 Result:
 ${output.result}`;
 
-      const displayContent = `
+      const displayContent =
-Subagent ${this.definition.name} Finished
+        output.terminate_reason === AgentTerminateMode.GOAL
+          ? displayResult
+          : `
+### Subagent ${this.definition.name} Finished Early
 
-Termination Reason:\n ${output.terminate_reason}
+**Termination Reason:** ${output.terminate_reason}
 
-Result:
+**Result/Summary:**
 ${displayResult}
 `;