diff --git a/modules/agents/pi/extensions/subagents/runner.test.ts b/modules/agents/pi/extensions/subagents/runner.test.ts
new file mode 100644
index 0000000..cd5ca2f
--- /dev/null
+++ b/modules/agents/pi/extensions/subagents/runner.test.ts
@@ -0,0 +1,65 @@
+import assert from "node:assert/strict";
+import childProcess from "node:child_process";
+import { EventEmitter } from "node:events";
+import { fileURLToPath } from "node:url";
+import test from "node:test";
+import type { RunnerEvents } from "./types.ts";
+
+class FakeStream extends EventEmitter {
+  setEncoding(_encoding: BufferEncoding): void {}
+
+  write(_chunk: string, callback?: (error?: Error | null) => void): boolean {
+    callback?.();
+    return true;
+  }
+
+  end(): void {}
+}
+
+function events(): RunnerEvents {
+  return {
+    accepted: () => {},
+    running: () => {},
+    settling: () => {},
+    completed: () => {},
+    failed: () => {},
+  };
+}
+
+test("child RPC process disables discovery while explicitly loading subagents extension", async (t) => {
+  const calls: Array<{ command: string; args: string[] }> = [];
+  const fakeChild = new EventEmitter() as EventEmitter & {
+    stdout: FakeStream;
+    stderr: FakeStream;
+    stdin: FakeStream;
+    killed: boolean;
+    pid?: number;
+    kill(signal?: NodeJS.Signals): boolean;
+  };
+  fakeChild.stdout = new FakeStream();
+  fakeChild.stderr = new FakeStream();
+  fakeChild.stdin = new FakeStream();
+  fakeChild.killed = false;
+  fakeChild.kill = () => {
+    fakeChild.killed = true;
+    return true;
+  };
+  const spawn = t.mock.method(childProcess, "spawn", (command, args) => {
+    calls.push({ command: String(command), args: Array.isArray(args) ? args.map(String) : [] });
+    return fakeChild as unknown as childProcess.ChildProcessWithoutNullStreams;
+  });
+
+  const { SubprocessRpcRunner } = await import("./runner.ts");
+  const runner = new SubprocessRpcRunner();
+  await runner.start("child-1", { prompt: "work" }, "/tmp", events());
+
+  assert.equal(spawn.mock.callCount(), 1);
+  const args = calls[0].args;
+  const noExtensionsIndex = args.indexOf("--no-extensions");
+  const extensionIndex = args.indexOf("--extension");
+
+  assert.notEqual(noExtensionsIndex, -1, "child args keep automatic extension discovery disabled");
+  assert.notEqual(extensionIndex, -1, "child args explicitly load the subagents extension entry");
+  assert.equal(args[extensionIndex + 1], fileURLToPath(new URL("./index.ts", import.meta.url)));
+  assert.ok(noExtensionsIndex < extensionIndex);
+});
diff --git a/modules/agents/pi/extensions/subagents/runner.ts b/modules/agents/pi/extensions/subagents/runner.ts
index 7231fa8..7804f7b 100644
--- a/modules/agents/pi/extensions/subagents/runner.ts
+++ b/modules/agents/pi/extensions/subagents/runner.ts
@@ -1,4 +1,5 @@
 import { spawn, type ChildProcessWithoutNullStreams } from "node:child_process";
+import { fileURLToPath } from "node:url";
 import type { ChildHandle, ChildRunner, RunnerEvents, SpawnRequest } from "./types.ts";
 
 interface PendingResponse {
@@ -156,7 +157,7 @@ class RpcChildHandle implements ChildHandle {
 
 export class SubprocessRpcRunner implements ChildRunner {
   async start(id: string, request: SpawnRequest, cwd: string, events: RunnerEvents): Promise<ChildHandle> {
-    const args = [process.argv[1], "--mode", "rpc", "--no-extensions", "--name", `subagent ${id}`, ...contextArgs(request), ...toolArgs(request), ...modelArgs(request)];
+    const args = [process.argv[1], "--mode", "rpc", "--no-extensions", "--extension", subagentsExtensionPath(), "--name", `subagent ${id}`, ...contextArgs(request), ...toolArgs(request), ...modelArgs(request)];
     const child = spawn(process.execPath, args, {
       cwd,
       env: childEnvironment(),
@@ -174,6 +175,10 @@ function delay(ms: number): Promise<void> {
   return new Promise((resolve) => setTimeout(resolve, ms));
 }
 
+function subagentsExtensionPath(): string {
+  return fileURLToPath(new URL("./index.ts", import.meta.url));
+}
+
 function contextArgs(request: SpawnRequest): string[] {
   if (request.context !== "fork" || !request.parentSessionFile) return [];
   return ["--fork", request.parentSessionFile];