update readme and installer

tests/install.test.ts

@@ -265,6 +265,30 @@ test("installer writes empty option skeletons, fills only missing keys, and is i
     expect(await contents(f.config)).toEqual(filled);
 });
 
+test("agents installs set experimental.subagent_depth to at least 2", async () => {
+    const f = await fixture();
+    await install(f.source, f.config, "quota");
+    expect((await contents(f.config)).experimental).toBeUndefined();
+    await install(f.source, f.config, "agents");
+    const fresh = await contents(f.config);
+    expect(fresh.experimental).toEqual({ subagent_depth: 2 });
+    expect(fresh).toMatchObject(unrelated);
+    for (const [depth, expected] of [
+        [1, 2],
+        [3, 3],
+    ]) {
+        await writeFile(
+            join(f.config, "opencode.json"),
+            JSON.stringify({ ...fresh, experimental: { subagent_depth: depth, other: true } }),
+        );
+        await install(f.source, f.config);
+        const result = await contents(f.config);
+        expect(result.experimental).toEqual({ subagent_depth: expected, other: true });
+        await install(f.source, f.config);
+        expect(await contents(f.config)).toEqual(result);
+    }
+});
+
 test("local installer retains executable permissions and supports direct invocation", async () => {
     const f = await fixture();
     const path = new URL("../install-local.sh", import.meta.url).pathname;