fix(config): enforce default-free persistence in write path

src/config/io.write-config.test.ts

@@ -0,0 +1,47 @@
+import fs from "node:fs/promises";
+import path from "node:path";
+import { describe, expect, it } from "vitest";
+import { createConfigIO } from "./io.js";
+import { withTempHome } from "./test-helpers.js";
+
+describe("config io write", () => {
+  it("persists caller changes onto resolved config without leaking runtime defaults", async () => {
+    await withTempHome(async (home) => {
+      const configPath = path.join(home, ".openclaw", "openclaw.json");
+      await fs.mkdir(path.dirname(configPath), { recursive: true });
+      await fs.writeFile(
+        configPath,
+        JSON.stringify({ gateway: { port: 18789 } }, null, 2),
+        "utf-8",
+      );
+
+      const io = createConfigIO({
+        env: {} as NodeJS.ProcessEnv,
+        homedir: () => home,
+      });
+
+      const snapshot = await io.readConfigFileSnapshot();
+      expect(snapshot.valid).toBe(true);
+
+      const next = structuredClone(snapshot.config);
+      next.gateway = {
+        ...next.gateway,
+        auth: { mode: "token" },
+      };
+
+      await io.writeConfigFile(next);
+
+      const persisted = JSON.parse(await fs.readFile(configPath, "utf-8")) as Record<
+        string,
+        unknown
+      >;
+      expect(persisted.gateway).toEqual({
+        port: 18789,
+        auth: { mode: "token" },
+      });
+      expect(persisted).not.toHaveProperty("agents.defaults");
+      expect(persisted).not.toHaveProperty("messages.ackReaction");
+      expect(persisted).not.toHaveProperty("sessions.persistence");
+    });
+  });
+});