test(agent-core): invoke the saved skill instead of only listing it

Asserting the Skill tool is present and the registry holds the skill does
not exercise the lookup that activation performs. Call the tool with
audit-routes and check it does not error, so a broken lookup fails the test
that claims the skill is invocable.

Author: elkaix

packages/agent-core/test/session/init.test.ts

@@ -1259,10 +1259,16 @@ describe('AgentAPI.startBtw', () => {
 
       // The tool reads the registry as it runs, so the reload is all it needs
       // to reach a skill written after the session opened.
-      expect(main.tools.loopTools.map((tool) => tool.name)).toContain('Skill');
-      expect(
-        (await session.listSkills()).map((skill) => skill.name),
-      ).toContain('audit-routes');
+      const skill = main.tools.loopTools.find((tool) => tool.name === 'Skill');
+      expect(skill).toBeDefined();
+      const result = await executeTool(skill!, {
+        turnId: '0',
+        toolCallId: 'call_skill',
+        args: { skill: 'audit-routes' },
+        signal: new AbortController().signal,
+      });
+      expect(result.isError).not.toBe(true);
+      expect(JSON.stringify(result.output)).toContain('audit-routes');
       expect(setActiveTools).not.toHaveBeenCalled();
     } finally {
       await session.close();