test(core): add comprehensive UX tests for agent loading error formatting

packages/core/src/agents/agentLoader.test.ts

@@ -242,6 +242,99 @@ Body`);
         /Name must be a valid slug/,
       );
     });
+
+    describe('error formatting and kind inference', () => {
+      it('should only show local agent errors when kind is inferred as local (via kind field)', async () => {
+        const filePath = await writeAgentMarkdown(`---
+kind: local
+name: invalid-local
+# missing description
+---
+Body`);
+        const error = await parseAgentMarkdown(filePath).catch((e) => e);
+        expect(error).toBeInstanceOf(AgentLoadError);
+        expect(error.message).toContain('Validation failed');
+        expect(error.message).toContain('description: Required');
+        expect(error.message).not.toContain('Remote Agent');
+      });
+
+      it('should only show local agent errors when kind is inferred as local (via local-specific keys)', async () => {
+        const filePath = await writeAgentMarkdown(`---
+name: invalid-local
+# missing description
+tools:
+  - run_shell_command
+---
+Body`);
+        const error = await parseAgentMarkdown(filePath).catch((e) => e);
+        expect(error).toBeInstanceOf(AgentLoadError);
+        expect(error.message).toContain('Validation failed');
+        expect(error.message).toContain('description: Required');
+        expect(error.message).not.toContain('Remote Agent');
+      });
+
+      it('should only show remote agent errors when kind is inferred as remote (via kind field)', async () => {
+        const filePath = await writeAgentMarkdown(`---
+kind: remote
+name: invalid-remote
+# missing agent_card_url
+---
+Body`);
+        const error = await parseAgentMarkdown(filePath).catch((e) => e);
+        expect(error).toBeInstanceOf(AgentLoadError);
+        expect(error.message).toContain('Validation failed');
+        expect(error.message).toContain('agent_card_url: Required');
+        expect(error.message).not.toContain('Local Agent');
+      });
+
+      it('should only show remote agent errors when kind is inferred as remote (via remote-specific keys)', async () => {
+        const filePath = await writeAgentMarkdown(`---
+name: invalid-remote
+auth:
+  type: apiKey
+  key: my_key
+# missing agent_card_url
+---
+Body`);
+        const error = await parseAgentMarkdown(filePath).catch((e) => e);
+        expect(error).toBeInstanceOf(AgentLoadError);
+        expect(error.message).toContain('Validation failed');
+        expect(error.message).toContain('agent_card_url: Required');
+        expect(error.message).not.toContain('Local Agent');
+      });
+
+      it('should show errors for both types when kind cannot be inferred', async () => {
+        const filePath = await writeAgentMarkdown(`---
+name: invalid-unknown
+# missing description and missing agent_card_url, no specific keys
+---
+Body`);
+        const error = await parseAgentMarkdown(filePath).catch((e) => e);
+        expect(error).toBeInstanceOf(AgentLoadError);
+        expect(error.message).toContain('Validation failed');
+        expect(error.message).toContain('(Local Agent)');
+        expect(error.message).toContain('(Remote Agent)');
+        expect(error.message).toContain('description: Required');
+        expect(error.message).toContain('agent_card_url: Required');
+      });
+
+      it('should format errors without a stray colon when the path is empty (e.g. strict object with unknown keys)', async () => {
+        const filePath = await writeAgentMarkdown(`---
+kind: local
+name: my-agent
+description: test
+unknown_field: true
+---
+Body`);
+        const error = await parseAgentMarkdown(filePath).catch((e) => e);
+        expect(error).toBeInstanceOf(AgentLoadError);
+        expect(error.message).toContain(
+          "Unrecognized key(s) in object: 'unknown_field'",
+        );
+        expect(error.message).not.toContain(': Unrecognized key(s)');
+        expect(error.message).not.toContain('Required');
+      });
+    });
   });
 
   describe('markdownToAgentDefinition', () => {

packages/core/src/agents/agentLoader.ts

@@ -244,14 +244,18 @@ function formatZodError(
               return null;
 
             const unionIssues = unionError.issues
-              .map((u) => `${u.path.join('.')}: ${u.message}`)
+              .map((u) => {
+                const pathStr = u.path.join('.');
+                return pathStr ? `${pathStr}: ${u.message}` : u.message;
+              })
               .join(', ');
             return `(${label}) ${unionIssues}`;
           })
           .filter(Boolean)
           .join('\n');
       }
-      return `${i.path.join('.')}: ${i.message}`;
+      const pathStr = i.path.join('.');
+      return pathStr ? `${pathStr}: ${i.message}` : i.message;
     })
     .join('\n');
   return `${context}:\n${issues}`;