diff --git a/src/cli/index.ts b/src/cli/index.ts
index 93c963833b..9d37cb5c21 100755
--- a/src/cli/index.ts
+++ b/src/cli/index.ts
@@ -732,6 +732,9 @@ function reportRestartFailure(result: Extract<ProxyRestartResult, { ok: false }>
     if (code === "restart_capability_unsupported") {
       console.error("❌ The running proxy predates process-bound restart support; no unsafe fallback was attempted.");
       console.error("   After confirming this home owns the proxy, run `ocx stop` and then `ocx start` once.");
+    } else if (code === "restart_version_skew") {
+      console.error("❌ The running proxy reports a different OpenCodex version than this CLI; restarting in place would respawn the old installation.");
+      console.error("   Run `ocx stop` and then `ocx start` from this installation instead.");
     } else {
       console.error("❌ Proxy restart request could not be confirmed; no fallback stop/start was attempted.");
     }
diff --git a/src/cli/system-restart-client.ts b/src/cli/system-restart-client.ts
index fbc7c4548f..5f0e1ad2ab 100644
--- a/src/cli/system-restart-client.ts
+++ b/src/cli/system-restart-client.ts
@@ -22,6 +22,8 @@ import {
   type LiveProxy,
 } from "../server/proxy-liveness";
 import type { ProxyRestartRequestOutcome } from "./tray-proxy";
+import { packageVersion } from "./help";
+import { computeVersionSkew } from "./version-skew";
 
 export const SYSTEM_RESTART_REQUEST_TIMEOUT_MS = 5_000;
 export const SYSTEM_RESTART_ATTESTATION_TIMEOUT_MS = 4_000;
@@ -32,6 +34,8 @@ export interface BoundSystemRestartDeps {
   findLive?: typeof findLiveProxy;
   createChallenge?: () => string;
   now?: () => number;
+  /** Invoking CLI version for the skew guard; defaults to this bundle's package version. */
+  cliVersion?: string;
 }
 
 function rejected(code: string): ProxyRestartRequestOutcome {
@@ -107,6 +111,18 @@ export async function requestBoundSystemRestart(
     return rejected("restart_capability_unsupported");
   }
 
+  // An in-place restart respawns the live process from its own installation
+  // (selfLaunchArgv in server/management/system-restart.ts), so a restart accepted
+  // from a different-version CLI would keep the OLD build serving while reporting
+  // success (#4522). Both sides already publish exactly the data doctor's skew
+  // diagnosis compares (packageVersion vs the /healthz version), so reuse that
+  // comparison and refuse before POST. Placeholder versions (unknown/0.0.0) are
+  // "cannot compare", not mismatch, and keep the existing behavior.
+  const proxyVersion = typeof body.version === "string" ? body.version : undefined;
+  if (computeVersionSkew(deps.cliVersion ?? packageVersion(), proxyVersion).skewed) {
+    return rejected("restart_version_skew");
+  }
+
   let observed: LiveProxy | null;
   try {
     observed = await (deps.findLive ?? findLiveProxy)({ deadlineAt, nowFn: now });
diff --git a/tests/cli/system-restart-client.test.ts b/tests/cli/system-restart-client.test.ts
index f7c8c7657a..07b9e3a4e5 100644
--- a/tests/cli/system-restart-client.test.ts
+++ b/tests/cli/system-restart-client.test.ts
@@ -52,6 +52,9 @@ function successfulDeps() {
       findLive: async () => target,
       createChallenge: () => challenge,
       now: () => 1_000,
+      // Matches the /healthz fixture version below so the skew guard stays out of the way;
+      // the dedicated skew tests override it explicitly.
+      cliVersion: "test",
     },
   };
 }
@@ -144,6 +147,81 @@ describe("bound system restart client", () => {
     expect(setup.requests).toHaveLength(1);
   });
 
+  test("refuses a restart through a CLI whose version differs from the attested proxy", async () => {
+    for (const [proxyVersion, cliVersion] of [
+      ["2.49.0", "2.53.0"],
+      ["2.53.0", "2.49.0"],
+      ["test", "2.53.0"],
+    ] as const) {
+      const setup = successfulDeps();
+      setup.deps.cliVersion = cliVersion;
+      setup.deps.fetchImpl = (async (input: string | URL | Request, init?: RequestInit) => {
+        const url = String(input);
+        setup.requests.push({ url, init });
+        if (url.endsWith("/healthz")) {
+          const response = successfulDepsResponse(setup.secret, setup.challenge);
+          const body = await response.json() as Record<string, unknown>;
+          body.version = proxyVersion;
+          return new Response(JSON.stringify(body), {
+            status: 200,
+            headers: response.headers,
+          });
+        }
+        throw new Error("POST must not be attempted");
+      }) as typeof fetch;
+
+      const outcome = await requestBoundSystemRestart(target, 10_000, setup.deps);
+      expect(outcome).toMatchObject({ accepted: false, uncertain: false });
+      expect(outcome.accepted ? "" : (outcome.error as Error).message)
+        .toBe("restart_version_skew");
+      expect(setup.requests).toHaveLength(1);
+    }
+  });
+
+  test("allows a restart when the invoking CLI matches the attested proxy version", async () => {
+    const setup = successfulDeps();
+    setup.deps.cliVersion = "2.53.0";
+    setup.deps.fetchImpl = (async (input: string | URL | Request, init?: RequestInit) => {
+      const url = String(input);
+      setup.requests.push({ url, init });
+      if (url.endsWith("/healthz")) {
+        const response = successfulDepsResponse(setup.secret, setup.challenge);
+        const body = await response.json() as Record<string, unknown>;
+        body.version = "2.53.0";
+        return new Response(JSON.stringify(body), {
+          status: 200,
+          headers: response.headers,
+        });
+      }
+      return new Response(JSON.stringify({ success: true }), { status: 202 });
+    }) as typeof fetch;
+
+    expect(await requestBoundSystemRestart(target, 10_000, setup.deps)).toEqual({ accepted: true });
+    expect(setup.requests).toHaveLength(2);
+  });
+
+  test("treats a placeholder proxy version as incomparable and keeps the restart path", async () => {
+    const setup = successfulDeps();
+    setup.deps.cliVersion = "2.53.0";
+    setup.deps.fetchImpl = (async (input: string | URL | Request, init?: RequestInit) => {
+      const url = String(input);
+      setup.requests.push({ url, init });
+      if (url.endsWith("/healthz")) {
+        const response = successfulDepsResponse(setup.secret, setup.challenge);
+        const body = await response.json() as Record<string, unknown>;
+        body.version = "0.0.0";
+        return new Response(JSON.stringify(body), {
+          status: 200,
+          headers: response.headers,
+        });
+      }
+      return new Response(JSON.stringify({ success: true }), { status: 202 });
+    }) as typeof fetch;
+
+    expect(await requestBoundSystemRestart(target, 10_000, setup.deps)).toEqual({ accepted: true });
+    expect(setup.requests).toHaveLength(2);
+  });
+
   test("refuses to POST when the live target changes after attestation", async () => {
     const setup = successfulDeps();
     setup.deps.findLive = async () => ({ ...target, pid: 4343 });