diff --git a/src/server/management/native-integration-routes.ts b/src/server/management/native-integration-routes.ts
index 894c00960..b6754bed2 100644
--- a/src/server/management/native-integration-routes.ts
+++ b/src/server/management/native-integration-routes.ts
@@ -32,6 +32,13 @@ import type { ManagementContext } from "./context";
 
 export type NativeIntegrationClientId = "claude" | "grok" | "codex" | "claude-desktop";
 
+function isNativeToggleBody(body: unknown): body is { enabled: boolean } {
+  return typeof body === "object"
+    && body !== null
+    && !Array.isArray(body)
+    && typeof (body as { enabled?: unknown }).enabled === "boolean";
+}
+
 /** Every reason this module can decline, in one place (audit r3 #6). */
 export type NativeRefusalReason =
   | "not_installed"
@@ -289,14 +296,14 @@ async function handleCodexToggle(ctx: ManagementContext): Promise<Response> {
       "Another Codex change is already in flight. Nothing was written — try again in a moment.");
   }
   codexToggleFlight = (async (): Promise<Response> => {
-    let body: { enabled?: unknown };
+    let body: unknown;
     try {
       body = await readManagementJsonBody(req);
     } catch (error) {
       rethrowManagementBodyTooLarge(error);
       return jsonResponse({ error: "invalid JSON body" }, 400);
     }
-    if (typeof body.enabled !== "boolean") {
+    if (!isNativeToggleBody(body)) {
       return jsonResponse({ error: "enabled must be a boolean" }, 400);
     }
     const enabled = body.enabled;
@@ -393,14 +400,14 @@ async function handleGrokToggle(ctx: ManagementContext): Promise<Response> {
       "Another Grok change is already in flight. Nothing was written — try again in a moment.");
   }
   grokToggleFlight = (async (): Promise<Response> => {
-    let body: { enabled?: unknown };
+    let body: unknown;
     try {
       body = await readManagementJsonBody(req);
     } catch (error) {
       rethrowManagementBodyTooLarge(error);
       return jsonResponse({ error: "invalid JSON body" }, 400);
     }
-    if (typeof body.enabled !== "boolean") {
+    if (!isNativeToggleBody(body)) {
       return jsonResponse({ error: "enabled must be a boolean" }, 400);
     }
     const enabled = body.enabled;
@@ -606,14 +613,14 @@ async function handleClaudeDesktopToggle(ctx: ManagementContext): Promise<Respon
       "Another Claude Desktop change is already in flight. Nothing was written — try again in a moment.");
   }
   claudeDesktopToggleFlight = (async (): Promise<Response> => {
-    let body: { enabled?: unknown };
+    let body: unknown;
     try {
       body = await readManagementJsonBody(ctx.req);
     } catch (error) {
       rethrowManagementBodyTooLarge(error);
       return jsonResponse({ error: "invalid JSON body" }, 400);
     }
-    if (typeof body.enabled !== "boolean") return jsonResponse({ error: "enabled must be a boolean" }, 400);
+    if (!isNativeToggleBody(body)) return jsonResponse({ error: "enabled must be a boolean" }, 400);
 
     const { setIntegrationEnabled } = await import("../../codex/desired-state");
     const persisted = setIntegrationEnabled("claude-desktop", body.enabled);
@@ -689,14 +696,14 @@ export async function handleNativeIntegrationRoutes(ctx: ManagementContext): Pro
   }
 
   if (url.pathname === "/api/native-integrations/claude" && req.method === "PUT") {
-    let body: { enabled?: unknown };
+    let body: unknown;
     try {
       body = await readManagementJsonBody(req);
     } catch (error) {
       rethrowManagementBodyTooLarge(error);
       return jsonResponse({ error: "invalid JSON body" }, 400);
     }
-    if (typeof body.enabled !== "boolean") {
+    if (!isNativeToggleBody(body)) {
       return jsonResponse({ error: "enabled must be a boolean" }, 400);
     }
 
@@ -722,6 +729,8 @@ export async function handleNativeIntegrationRoutes(ctx: ManagementContext): Pro
      * subscription — a failure that surfaces nowhere near this route.
      */
     if (!next.authModeMigratedAt) next.authModeMigratedAt = new Date().toISOString();
+    const hadClaudeCode = Object.prototype.hasOwnProperty.call(config, "claudeCode");
+    const previousClaudeCode = config.claudeCode;
     config.claudeCode = next;
 
     /*
@@ -732,6 +741,11 @@ export async function handleNativeIntegrationRoutes(ctx: ManagementContext): Pro
     try {
       persist(config);
     } catch (error) {
+      // Persistence is the commit point. A failed lock acquisition must not
+      // leave the live server snapshot ahead of disk or make a retry look
+      // idempotent and skip the write entirely.
+      if (hadClaudeCode) config.claudeCode = previousClaudeCode;
+      else delete config.claudeCode;
       if (isConfigLockError(error)) {
         return isLockContention(error)
           ? refusal(409, "claude", "config_busy",
diff --git a/tests/native-claude-code-toggle.test.ts b/tests/native-claude-code-toggle.test.ts
index d6f0777ce..3da0b4ced 100644
--- a/tests/native-claude-code-toggle.test.ts
+++ b/tests/native-claude-code-toggle.test.ts
@@ -117,6 +117,23 @@ test("a non-boolean enabled is rejected", async () => {
   expect(res!.status).toBe(400);
 });
 
+test("non-object bodies are rejected without mutating or saving", async () => {
+  for (const rawBody of ["null", "[]", "true", "1", '"yes"']) {
+    const config = baseConfig({ claudeCode: { enabled: true } });
+    const before = structuredClone(config);
+    const { response, saved } = dispatch(config, "/api/native-integrations/claude", {
+      method: "PUT",
+      headers: { "Content-Type": "application/json" },
+      body: rawBody,
+    });
+    const res = await response;
+    expect(res!.status).toBe(400);
+    expect(await res!.json()).toEqual({ error: "enabled must be a boolean" });
+    expect(config).toEqual(before);
+    expect(saved).toHaveLength(0);
+  }
+});
+
 test("genuine lock contention refuses 409 config_busy, a broken lock is a 500", async () => {
   /*
    * `ConfigMutationLockError` wraps EVERY acquisition failure behind one
@@ -201,25 +218,24 @@ test("a held REAL config transaction refuses 409 config_busy, and release lets a
         {},
       );
     };
-    const refused = await putReal(baseConfig({ claudeCode: { enabled: true } }));
+    const config = baseConfig({ claudeCode: { enabled: true } });
+    const refused = await putReal(config);
     expect(refused!.status).toBe(409);
     const refusedBody = await refused!.json() as { code: string; reason: string };
     expect(refusedBody.code).toBe("native_integration_refused");
     expect(refusedBody.reason).toBe("config_busy");
+    expect(config.claudeCode?.enabled).toBe(true);
 
     holder.exec("ROLLBACK");
     holder.close();
-    /*
-     * A FRESH config object, not the refused one (wp3 A-gate): the route
-     * mutates the in-memory config before persistence, so the refused object
-     * already reads disabled and would short-circuit at the idempotent guard
-     * without ever re-acquiring the lock.
-     */
-    const retry = await putReal(baseConfig({ claudeCode: { enabled: true } }));
+    // Retry the exact live object that saw the refusal. A failed save must
+    // restore it so the retry re-acquires the lock and persists the change.
+    const retry = await putReal(config);
     expect(retry!.status).toBe(200);
     const retryBody = await retry!.json() as { changed: boolean; state: string };
     expect(retryBody.changed).toBe(true);
     expect(retryBody.state).toBe("absent");
+    expect(config.claudeCode?.enabled).toBe(false);
   } finally {
     try { holder.exec("ROLLBACK"); } catch { /* already closed */ }
     try { holder.close(); } catch { /* already closed */ }
diff --git a/tests/native-claude-desktop-toggle.test.ts b/tests/native-claude-desktop-toggle.test.ts
index 9b1844f01..2ac636b23 100644
--- a/tests/native-claude-desktop-toggle.test.ts
+++ b/tests/native-claude-desktop-toggle.test.ts
@@ -60,6 +60,18 @@ afterEach(() => {
   rmSync(root, { recursive: true, force: true });
 });
 
+test("a null toggle body is rejected before desired state or Desktop files change", async () => {
+  const response = await dispatch("/api/native-integrations/claude-desktop", {
+    method: "PUT",
+    headers: { "Content-Type": "application/json" },
+    body: "null",
+  });
+  expect(response!.status).toBe(400);
+  expect(await response!.json()).toEqual({ error: "enabled must be a boolean" });
+  expect(persistedIntent()).toBeUndefined();
+  expect(existsSync(library)).toBe(false);
+});
+
 test("the native route advertises Claude Desktop and OFF persists intent before removal", async () => {
   let sawPersistedOff = false;
   const result = await toggle(false, {
diff --git a/tests/native-codex-toggle.test.ts b/tests/native-codex-toggle.test.ts
index 9aa62df73..c16f93a00 100644
--- a/tests/native-codex-toggle.test.ts
+++ b/tests/native-codex-toggle.test.ts
@@ -90,6 +90,13 @@ afterEach(() => {
 });
 
 describe("request validation", () => {
+  test("a null body is rejected before anything is written", async () => {
+    const result = await put(baseConfig(), null);
+    expect(result.status).toBe(400);
+    expect(result.body).toEqual({ error: "enabled must be a boolean" });
+    expect(persistedCodexIntent()).toBeUndefined();
+  });
+
   test("a non-boolean enabled is rejected before anything is written", async () => {
     const result = await put(baseConfig(), { enabled: "false" });
     expect(result.status).toBe(400);
diff --git a/tests/native-grok-toggle.test.ts b/tests/native-grok-toggle.test.ts
index 2a405e9e3..e3fd89417 100644
--- a/tests/native-grok-toggle.test.ts
+++ b/tests/native-grok-toggle.test.ts
@@ -146,6 +146,19 @@ test("GET reports not-installed when GROK_HOME is missing", async () => {
   expect(row.state).toBe("absent");
 });
 
+test("a null toggle body is rejected before the Grok config is touched", async () => {
+  writeConfig("# user only\n");
+  const before = readConfig();
+  const response = await dispatch(baseConfig(), "/api/native-integrations/grok", {
+    method: "PUT",
+    headers: { "Content-Type": "application/json" },
+    body: "null",
+  });
+  expect(response!.status).toBe(400);
+  expect(await response!.json()).toEqual({ error: "enabled must be a boolean" });
+  expect(readConfig()).toBe(before);
+});
+
 test("GET reports unsafe and blocks the switch on an orphaned marker", async () => {
   writeConfig(`# user\n${BEGIN}\n[model.ocx-a]\n`);
   const row = await get(baseConfig());