feat: enable permission-aware subagents

pi-subagents/test/fixtures/ext-alpha.mjs

@@ -0,0 +1,23 @@
+/**
+ * Real extension fixture "alpha" for the template-driven e2e runner.
+ * Registers two tools so narrowing (ext:ext-alpha.mjs/alpha_read) can be
+ * distinguished from exposing the whole extension. Plain ESM so node imports
+ * it without a TS transform; lives inside the repo tree so `@sinclair/typebox`
+ * resolves. Tools are never invoked by the runner — it only inspects the
+ * session's active tool set — so execute() is a trivial stub.
+ */
+import { Type } from "@sinclair/typebox";
+
+export default function (pi) {
+  for (const name of ["alpha_read", "alpha_write"]) {
+    pi.registerTool({
+      name,
+      label: name,
+      description: `Alpha extension tool ${name} (e2e fixture).`,
+      parameters: Type.Object({}),
+      async execute() {
+        return { content: [{ type: "text", text: name }] };
+      },
+    });
+  }
+}