diff --git a/scripts/run-product-tests.mjs b/scripts/run-product-tests.mjs
index e28f7773..8d71b11e 100644
--- a/scripts/run-product-tests.mjs
+++ b/scripts/run-product-tests.mjs
@@ -87,6 +87,10 @@ async function collectTests(directory, prefix = '') {
   return files;
 }
 
+// 端末の本物のhost設定の置き場を指す変数（`src/setup-hosts.mjs`が読む）。試験は一時のHOMEを渡すが、
+// これらが残っていると、CLIはHOMEでなくそちらを使い、利用者の本物の設定を書き換える。
+export const HOST_CONFIG_ENV = Object.freeze(['CLAUDE_CONFIG_DIR', 'CODEX_HOME', 'GROK_HOME']);
+
 export function productTestEnvironment(parentEnv = process.env) {
   // product gateはsuite単位ですでに全CPU並列である。各integration fixtureが
   // sensor init用WASM poolまで最大8本prewarmするとnested oversubscriptionになり、
@@ -95,6 +99,7 @@ export function productTestEnvironment(parentEnv = process.env) {
   const env = { ...parentEnv, LATTICE_DASHBOARD_AUTOSTART: '0',
     LATTICE_SENSOR_PARSE_WORKERS: '1' };
   delete env.FORCE_COLOR;
+  for (const name of HOST_CONFIG_ENV) delete env[name];
   return env;
 }
 
diff --git a/test/hooks-cli.test.mjs b/test/hooks-cli.test.mjs
index f290d42e..899b2002 100644
--- a/test/hooks-cli.test.mjs
+++ b/test/hooks-cli.test.mjs
@@ -11,6 +11,7 @@ import { tmpdir } from 'node:os';
 import path from 'node:path';
 import { fileURLToPath } from 'node:url';
 import nodeTest, { after, before } from 'node:test';
+import { HOST_CONFIG_ENV } from '../scripts/run-product-tests.mjs';
 import { resolveStableNodePath, runHooksCli } from '../src/hooks-cli.mjs';
 
 const test = process.platform === 'win32' ? nodeTest.skip : nodeTest;
@@ -79,8 +80,12 @@ after(async () => {
 
 function isolatedEnv({ home = suiteHome, stateHome = suiteState, configHome = suiteConfig,
   extraEnv = {} } = {}) {
+  // 端末の本物のhost設定の置き場を指す変数は渡さない。残っていると、CLIは下のHOMEでなくそちらを使い、
+  // 利用者の本物の設定を書き換える。
+  const inherited = { ...process.env };
+  for (const name of HOST_CONFIG_ENV) delete inherited[name];
   const env = {
-    ...process.env,
+    ...inherited,
     ...extraEnv,
     HOME: home,
     XDG_STATE_HOME: stateHome,
@@ -598,6 +603,38 @@ test('P4 F6: pending receipt回復はlock取得後にconfigを再読してcommit
 });
 
 // C3-1: host home dir不在はHOST_NOT_PRESENT exit 1で、dirを作らない。
+// 試験を起こした端末が`CODEX_HOME`等を持っていても、CLIへ渡すのは試験のHOMEだけである。
+// 2026-10-03: `CODEX_HOME`を持つ端末でこの試験を走らせ、共有の本物のCodex hooks.jsonを書き換えた。
+test('試験のCLIは、端末のCODEX_HOME・CLAUDE_CONFIG_DIR・GROK_HOMEが指す本物の設定へ触れない', async (t) => {
+  const decoy = await mkdtemp(path.join(tmpdir(), 'lattice-hooks-decoy-'));
+  t.after(() => rm(decoy, { recursive: true, force: true }));
+  const saved = Object.fromEntries(HOST_CONFIG_ENV.map((name) => [name, process.env[name]]));
+  t.after(() => {
+    for (const [name, value] of Object.entries(saved)) {
+      if (value === undefined) delete process.env[name];
+      else process.env[name] = value;
+    }
+  });
+  // 本物の代わりのフォルダを指させる。中へ設定を置き、試験の後も1 byteも変わっていないことを見る。
+  const decoyHooks = path.join(decoy, 'hooks.json');
+  const decoySettings = path.join(decoy, 'settings.json');
+  await writeFile(decoyHooks, FOREIGN_CODEX_HOOKS, { mode: 0o600 });
+  await writeFile(decoySettings, '{}\n', { mode: 0o600 });
+  for (const name of HOST_CONFIG_ENV) process.env[name] = decoy;
+  const before = [await snapshotFile(decoyHooks), await snapshotFile(decoySettings)];
+
+  for (const host of ['codex', 'claude']) {
+    const fixture = await hooksFixture(t, host, { config: host === 'codex' ? FOREIGN_CODEX_HOOKS : '{}\n' });
+    assert.equal(runCli(['hooks', 'install', '--host', host], options(fixture)).status, 0, host);
+    assert.equal(handlers(await readJson(fixture.configPath))
+      .filter((item) => commandArgv(item.command).includes('hooks')).length, 1, host);
+    assert.equal(runCli(['hooks', 'uninstall', '--host', host], options(fixture)).status, 0, host);
+  }
+
+  assert.deepEqual([await snapshotFile(decoyHooks), await snapshotFile(decoySettings)], before);
+  assert.deepEqual((await readdir(decoy)).sort(), ['hooks.json', 'settings.json']);
+});
+
 test('P3 C3-1: host home dir不在は HOST_NOT_PRESENT exit 1、設定dirを作らずに終了する', async (t) => {
   for (const host of ['claude', 'codex', 'cursor']) {
     const fixture = await hooksFixture(t, host, { createHost: false });
diff --git a/test/product-test-runner.test.mjs b/test/product-test-runner.test.mjs
index 31069a1b..7853901a 100644
--- a/test/product-test-runner.test.mjs
+++ b/test/product-test-runner.test.mjs
@@ -32,6 +32,16 @@ test('product test child envはFORCE_COLORを除去しdashboard autostartを無
   });
 });
 
+test('product test child envは、端末の本物のhost設定を指す変数を渡さない', () => {
+  // これらが残ると、一時のHOMEを渡した試験のCLIが、利用者の本物のCodex・Claude・Grokの設定を書き換える。
+  const parentEnv = { PATH: '/fixture/bin', CODEX_HOME: '/real/.codex', CLAUDE_CONFIG_DIR: '/real/.claude',
+    GROK_HOME: '/real/.grok' };
+  const childEnv = productTestEnvironment(parentEnv);
+  for (const name of ['CODEX_HOME', 'CLAUDE_CONFIG_DIR', 'GROK_HOME']) assert.equal(Object.hasOwn(childEnv, name), false, name);
+  assert.equal(childEnv.PATH, '/fixture/bin');
+  assert.equal(parentEnv.CODEX_HOME, '/real/.codex');
+});
+
 test('環境別profileはfocused再現用のsuiteだけを選びcoreの総当たりを複製しない', () => {
   const retired = 'control-compiler.test.mjs';
   const all = [