diff --git a/extensions/migrate-hermes/model.apply.test.ts b/extensions/migrate-hermes/model.apply.test.ts
index 9e8edf20d9c..2018786852e 100644
--- a/extensions/migrate-hermes/model.apply.test.ts
+++ b/extensions/migrate-hermes/model.apply.test.ts
@@ -3,7 +3,13 @@ import type { OpenClawConfig } from "openclaw/plugin-sdk/provider-auth";
 import { afterEach, describe, expect, it } from "vitest";
 import { HERMES_REASON_DEFAULT_MODEL_CONFIGURED } from "./items.js";
 import { buildHermesMigrationProvider } from "./provider.js";
-import { cleanupTempRoots, makeContext, makeTempRoot, writeFile } from "./test/provider-helpers.js";
+import {
+  cleanupTempRoots,
+  makeConfigRuntime,
+  makeContext,
+  makeTempRoot,
+  writeFile,
+} from "./test/provider-helpers.js";
 
 describe("Hermes migration model apply", () => {
   afterEach(async () => {
@@ -34,14 +40,9 @@ describe("Hermes migration model apply", () => {
     } as OpenClawConfig;
     let writtenConfig: OpenClawConfig | undefined;
     const provider = buildHermesMigrationProvider({
-      runtime: {
-        config: {
-          loadConfig: () => existingConfig,
-          writeConfigFile: async (next: OpenClawConfig) => {
-            writtenConfig = next;
-          },
-        },
-      } as never,
+      runtime: makeConfigRuntime(existingConfig, (next) => {
+        writtenConfig = next;
+      }),
     });
 
     const result = await provider.apply(
@@ -103,14 +104,9 @@ describe("Hermes migration model apply", () => {
     } as OpenClawConfig;
     let writtenConfig: OpenClawConfig | undefined;
     const provider = buildHermesMigrationProvider({
-      runtime: {
-        config: {
-          loadConfig: () => existingConfig,
-          writeConfigFile: async (next: OpenClawConfig) => {
-            writtenConfig = next;
-          },
-        },
-      } as never,
+      runtime: makeConfigRuntime(existingConfig, (next) => {
+        writtenConfig = next;
+      }),
     });
 
     const result = await provider.apply(
@@ -157,16 +153,8 @@ describe("Hermes migration model apply", () => {
         },
       },
     } as OpenClawConfig;
-    let writeCalled = false;
     const provider = buildHermesMigrationProvider({
-      runtime: {
-        config: {
-          loadConfig: () => lateConfig,
-          writeConfigFile: async () => {
-            writeCalled = true;
-          },
-        },
-      } as never,
+      runtime: makeConfigRuntime(lateConfig),
     });
     const ctx = makeContext({ source, stateDir, workspaceDir, reportDir });
     const plan = await provider.plan(ctx);
@@ -183,6 +171,6 @@ describe("Hermes migration model apply", () => {
       ]),
     );
     expect(result.summary.conflicts).toBe(1);
-    expect(writeCalled).toBe(false);
+    expect(lateConfig.agents?.defaults?.model).toBe("anthropic/claude-sonnet-4.6");
   });
 });
diff --git a/extensions/migrate-hermes/test/provider-helpers.ts b/extensions/migrate-hermes/test/provider-helpers.ts
index 2d3632f74bb..84a17a39c62 100644
--- a/extensions/migrate-hermes/test/provider-helpers.ts
+++ b/extensions/migrate-hermes/test/provider-helpers.ts
@@ -33,6 +33,24 @@ export async function writeFile(filePath: string, content: string) {
   await fs.writeFile(filePath, content, "utf8");
 }
 
+export function makeConfigRuntime(
+  config: OpenClawConfig,
+  onWrite?: (next: OpenClawConfig) => void,
+): NonNullable<MigrationProviderContext["runtime"]> {
+  return {
+    config: {
+      loadConfig: () => config,
+      writeConfigFile: async (next: OpenClawConfig) => {
+        for (const key of Object.keys(config) as Array<keyof OpenClawConfig>) {
+          delete config[key];
+        }
+        Object.assign(config, next);
+        onWrite?.(next);
+      },
+    },
+  } as NonNullable<MigrationProviderContext["runtime"]>;
+}
+
 export function makeContext(params: {
   source: string;
   stateDir: string;