feat: enable permission-aware subagents

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

@@ -0,0 +1,27 @@
+/**
+ * Real extension fixture "lazy" for the template-driven e2e runner.
+ *
+ * Registers its tool from `session_start` rather than at load — the shape that
+ * broke subagents in issue #125. pi-mcp does exactly this (it can only enumerate
+ * tools once its MCP servers connect), and eagerly connecting at load time would
+ * orphan child processes on pi's non-agent code paths.
+ *
+ * The point of the fixture is the TIMING: at `loader.reload()` this extension
+ * contributes no tools at all, so any scoping that snapshots the tool set then
+ * will drop `lazy_tool` permanently. See ext-alpha.mjs for the conventions.
+ */
+import { Type } from "@sinclair/typebox";
+
+export default function (pi) {
+  pi.on("session_start", () => {
+    pi.registerTool({
+      name: "lazy_tool",
+      label: "lazy_tool",
+      description: "Lazily-registered extension tool (e2e fixture).",
+      parameters: Type.Object({}),
+      async execute() {
+        return { content: [{ type: "text", text: "lazy_tool" }] };
+      },
+    });
+  });
+}