diff --git a/restricted-execution/service.mjs b/restricted-execution/service.mjs
index a4140b9..bde930c 100644
--- a/restricted-execution/service.mjs
+++ b/restricted-execution/service.mjs
@@ -1,12 +1,17 @@
 import { spawn } from "node:child_process";
 import { randomUUID } from "node:crypto";
 import { createServer, request as httpRequest } from "node:http";
-import { mkdtemp, readFile, writeFile, rm, open } from "node:fs/promises";
+import { mkdtemp, readFile, writeFile, rm, open, lstat, readdir } from "node:fs/promises";
 import { constants } from "node:fs";
 import { tmpdir } from "node:os";
 import { join, dirname } from "node:path";
 
-import { checkedSocketPath } from "../socket-address.mjs";
+import {
+  checkedSocketPath,
+  socketDirectory,
+  prepareSocketDirectory,
+  removeEmptySocketDirectory,
+} from "../socket-address.mjs";
 
 const abi = "quixos-transaction-ports-v1";
 /** Reserved supervisor faults are not authored domain rejections. A graph
@@ -329,15 +334,57 @@ export async function serveRestrictedRegistry(config, io = process) {
         }
         await engine.exited;
       }
+      const sameDirectory = async (directory, owner) => {
+        const current = await lstat(directory);
+        if (
+          !owner ||
+          !current.isDirectory() ||
+          current.dev !== owner.dev ||
+          current.ino !== owner.ino ||
+          current.uid !== owner.uid ||
+          current.mode & 0o077
+        )
+          throw fixedError("RESTRICTED_START_FAILED");
+      };
+      // A bounded ordinary-engine parent is private to this admitted lifetime.
+      // Never close/unlink through a replacement directory or release its lease
+      // while the original namespace's ownership remains uncertain.
+      if (engine.socketParent) {
+        await sameDirectory(engine.socketParent, engine.socketParentOwner);
+        if (engine.directory) await sameDirectory(engine.directory, engine.directoryOwner);
+        if (engine.broker) {
+          const current = await lstat(engine.broker).catch((error) => {
+            if (error.code !== "ENOENT") throw error;
+            return null;
+          });
+          if (
+            current &&
+            (!engine.brokerOwner ||
+              !current.isSocket() ||
+              current.dev !== engine.brokerOwner.dev ||
+              current.ino !== engine.brokerOwner.ino)
+          )
+            throw fixedError("RESTRICTED_START_FAILED");
+        }
+      }
       engine.server?.closeAllConnections();
       if (engine.server) await new Promise((resolve) => engine.server.close(resolve));
-      try {
-        if (engine.directory) await rm(engine.directory, { recursive: true, force: true });
-      } finally {
-        engines.delete(engine);
-        await engine.release?.();
-        changed();
+      if (engine.socketParent) {
+        await sameDirectory(engine.socketParent, engine.socketParentOwner);
+        if (engine.directory) await sameDirectory(engine.directory, engine.directoryOwner);
       }
+      if (engine.directory) await rm(engine.directory, { recursive: true, force: true });
+      if (engine.socketParent) {
+        await removeEmptySocketDirectory(engine.socketIdentity);
+        const remaining = await lstat(engine.socketParent).catch((error) => {
+          if (error.code !== "ENOENT") throw error;
+          return null;
+        });
+        if (remaining) throw fixedError("RESTRICTED_START_FAILED");
+      }
+      engines.delete(engine);
+      await engine.release?.();
+      changed();
     })();
     return engine.destroying;
   };
@@ -361,13 +408,24 @@ export async function serveRestrictedRegistry(config, io = process) {
       () => destroyEngine(engine),
     );
     if (!call.open) return;
+    let directoryRoot;
     if (config.sandboxIdentity) {
       // The privileged helper owns a fixed explicit /run root and requires
       // this exact basename. Keep its cross-UID ancestry and identity rules.
-      for (const filename of ["broker.sock", "engine.sock"])
-        checkedSocketPath(tmpdir() + "/qx-engine-XXXXXX/" + filename);
+      directoryRoot = tmpdir();
+    } else {
+      engine.socketIdentity = { kind: "restricted-engine", process: process.pid, lifetime: randomUUID() };
+      directoryRoot = socketDirectory(engine.socketIdentity);
     }
-    engine.directory = await mkdtemp(join(tmpdir(), "qx-engine-"));
+    for (const filename of ["broker.sock", "engine.sock"])
+      checkedSocketPath(directoryRoot + "/qx-engine-XXXXXX/" + filename);
+    if (!config.sandboxIdentity) {
+      engine.socketParent = await prepareSocketDirectory(engine.socketIdentity);
+      engine.socketParentOwner = await lstat(engine.socketParent);
+      if ((await readdir(engine.socketParent)).length) throw fixedError("RESTRICTED_START_FAILED");
+    }
+    engine.directory = await mkdtemp(join(directoryRoot, "qx-engine-"));
+    if (engine.socketParent) engine.directoryOwner = await lstat(engine.directory);
     if (!call.open) return;
     const broker = checkedSocketPath(join(engine.directory, "broker.sock"));
     engine.socket = checkedSocketPath(join(engine.directory, "engine.sock"));
@@ -416,10 +474,14 @@ export async function serveRestrictedRegistry(config, io = process) {
       }
     });
 
+    if (engine.socketParent) engine.broker = broker;
     await new Promise((resolve, reject) => {
       engine.server.once("error", reject);
       engine.server.listen(broker, resolve);
     });
+    if (engine.socketParent) {
+      engine.brokerOwner = await lstat(broker);
+    }
     const modules = { "entry.mjs": { js: workerSource }, "package.mjs": { js: packageSource } };
     for (const module of sdk) modules[module.name] = { js: module.source };
     const setting = { registryExport: config.registryExport, exports: config.exports, maxBytes: limits.maxBytes };
diff --git a/restricted-execution/service.test.mjs b/restricted-execution/service.test.mjs
index 5b6dc26..7ff2425 100644
--- a/restricted-execution/service.test.mjs
+++ b/restricted-execution/service.test.mjs
@@ -1,11 +1,12 @@
 import test from "node:test";
 import assert from "node:assert/strict";
 import { PassThrough } from "node:stream";
-import { mkdtemp, writeFile, rm } from "node:fs/promises";
+import { mkdtemp, writeFile, rm, mkdir, readdir, lstat } from "node:fs/promises";
 import { tmpdir } from "node:os";
-import { join } from "node:path";
+import { join, dirname } from "node:path";
 import { fileURLToPath } from "node:url";
 import { serveRestrictedRegistry, RestrictedEngineBudget } from "./service.mjs";
+import { socketDirectory, checkedSocketPath } from "../socket-address.mjs";
 
 const workerd = process.env.QUIXOS_TEST_WORKERD;
 if (!workerd) throw Error("Set QUIXOS_TEST_WORKERD to the pinned engine");
@@ -95,6 +96,50 @@ async function fixture(source, options = {}) {
 }
 const registry = (code) => `export const registry={exports:['test'],async invoke(request,channel){${code}}};`;
 
+test("real engine sockets and retirement are independent of deep Unicode TMPDIR", async () => {
+  const root = await mkdtemp(join(tmpdir(), "restricted-deep-"));
+  const deep = join(root, "保留された状態".repeat(12));
+  await mkdir(deep);
+  const oldTmp = process.env.TMPDIR;
+  const socketRoot = dirname(socketDirectory({ kind: "qualification-probe" }));
+  const names = async () =>
+    readdir(socketRoot).catch((error) => {
+      if (error.code !== "ENOENT") throw error;
+      return [];
+    });
+  const before = new Set(await names());
+  let f, namespace;
+  process.env.TMPDIR = deep;
+  try {
+    assert.ok(Buffer.byteLength(join(deep, "qx-engine-XXXXXX", "engine.sock")) > 100);
+    f = await fixture(registry("return request.input;"));
+    f.start("deep runtime");
+    const result = await f.receive();
+    assert.equal(result.status, "returned");
+    assert.equal(result.output, "deep runtime");
+    assert.equal(f.stats().starts, 1);
+    const created = (await names()).filter((name) => !before.has(name));
+    assert.equal(created.length, 1);
+    namespace = join(socketRoot, created[0]);
+    const engines = await readdir(namespace);
+    assert.equal(engines.length, 1);
+    for (const name of ["broker.sock", "engine.sock"]) {
+      const endpoint = checkedSocketPath(join(namespace, engines[0], name));
+      assert.ok((await lstat(endpoint)).isSocket());
+    }
+  } finally {
+    try {
+      await f?.close();
+    } finally {
+      if (oldTmp === undefined) delete process.env.TMPDIR;
+      else process.env.TMPDIR = oldTmp;
+    }
+  }
+  await assert.rejects(lstat(namespace), { code: "ENOENT" });
+  assert.ok((await lstat(deep)).isDirectory());
+  await rm(root, { recursive: true, force: true });
+});
+
 test("uncertain OS cleanup cannot release engine capacity", async () => {
   const budget = new RestrictedEngineBudget(1, async () => ({
     async release() {