feat: enable permission-aware subagents

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

@@ -0,0 +1,18 @@
+/**
+ * Real extension fixture "beta" for the template-driven e2e runner.
+ * Registers a single tool, used to prove that the `ext:` allowlist flip mutes
+ * a loaded-but-unselected extension. See ext-alpha.mjs for the conventions.
+ */
+import { Type } from "@sinclair/typebox";
+
+export default function (pi) {
+  pi.registerTool({
+    name: "beta_tool",
+    label: "beta_tool",
+    description: "Beta extension tool (e2e fixture).",
+    parameters: Type.Object({}),
+    async execute() {
+      return { content: [{ type: "text", text: "beta_tool" }] };
+    },
+  });
+}