diff --git a/test/codex-e2e-sol-scope.test.ts b/test/codex-e2e-sol-scope.test.ts
index 395d96746..862f7b8de 100644
--- a/test/codex-e2e-sol-scope.test.ts
+++ b/test/codex-e2e-sol-scope.test.ts
@@ -25,8 +25,19 @@ const CODEX_AVAILABLE = spawnSync('which', ['codex'], { timeout: 30_000 }).statu
 // The run pins the model with --ignore-user-config; older codex CLIs reject
 // the flag with an argv error indistinguishable from a Sol regression, so
 // probe support and skip (not fail) on old CLIs.
-const IGNORE_USER_CONFIG_SUPPORTED = CODEX_AVAILABLE
-  && (spawnSync('codex', ['exec', '--help'], { encoding: 'utf8', timeout: 120_000 }).stdout ?? '').includes('--ignore-user-config');
+// The probe runs in a private HOME and CODEX_HOME: every codex run writes
+// $CODEX_HOME/tmp/arg0, and module load must never touch the real ~/.codex.
+function codexSupportsIgnoreUserConfig(): boolean {
+  const home = fs.mkdtempSync(path.join(os.tmpdir(), 'codex-sol-probe-'));
+  try {
+    fs.mkdirSync(path.join(home, '.codex'));
+    const help = spawnSync('codex', ['exec', '--help'], {
+      encoding: 'utf8', timeout: 120_000, env: { ...process.env, HOME: home, CODEX_HOME: path.join(home, '.codex') },
+    });
+    return (help.stdout ?? '').includes('--ignore-user-config');
+  } finally { fs.rmSync(home, { recursive: true, force: true }); }
+}
+const IGNORE_USER_CONFIG_SUPPORTED = CODEX_AVAILABLE && codexSupportsIgnoreUserConfig();
 const evalsEnabled = !!process.env.EVALS;
 // External-service test — periodic tier only (CLAUDE.md tiering rule 3). The
 // positive guard shape below is what classifyPaidTestFile greps to exclude
diff --git a/test/codex-hardening.test.ts b/test/codex-hardening.test.ts
index 120a217ee..0a76657d7 100644
--- a/test/codex-hardening.test.ts
+++ b/test/codex-hardening.test.ts
@@ -956,3 +956,39 @@ describe('codex broken-install detection (#2742)', () => {
     expect(src).toContain('_CODEX_MP=$?');
   });
 });
+
+// --- Live codex smokes keep away from the real Codex home -------------------
+
+describe('live codex smokes run codex in a private HOME and CODEX_HOME', () => {
+  // Every codex run writes $CODEX_HOME/tmp/arg0. The two smokes below probe the
+  // CLI at module load or in free-tier tests, so with a real codex on PATH they
+  // used to write into the developer's ~/.codex.
+  for (const file of ['test/codex-resume-flag-semantics.test.ts', 'test/codex-e2e-sol-scope.test.ts']) {
+    test(`${file} never runs codex with the caller's HOME or Codex home`, () => {
+      const home = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-codex-smoke-home-'));
+      try {
+        const stubDir = path.join(home, 'stub-bin');
+        const log = path.join(home, 'codex-calls.log');
+        fs.mkdirSync(stubDir);
+        fs.writeFileSync(path.join(stubDir, 'codex'), `#!/usr/bin/env bash
+printf '%s|%s\\n' "$HOME" "\${CODEX_HOME:-unset}" >> "${log}"
+mkdir -p "\${CODEX_HOME:-$HOME/.codex}/tmp" && : > "\${CODEX_HOME:-$HOME/.codex}/tmp/arg0"
+printf 'Usage: codex exec [OPTIONS]\\n  -c, --config <key=value>  sandbox_mode\\n      --ignore-user-config\\n'
+`, { mode: 0o755 });
+        const r = spawnSync(process.execPath, ['test', file], {
+          cwd: ROOT, encoding: 'utf8', timeout: 120_000,
+          env: { PATH: `${stubDir}:${process.env.PATH ?? ''}`, HOME: home, TMPDIR: os.tmpdir() },
+        });
+        expect(r.status).toBe(0);
+        const calls = fs.readFileSync(log, 'utf8').trim().split('\n');
+        expect(calls.length).toBeGreaterThan(0);
+        for (const call of calls) {
+          const [callHome, codexHome] = call.split('|');
+          expect({ call, privateHome: callHome !== home, privateCodexHome: codexHome !== 'unset' && !codexHome!.startsWith(home) })
+            .toEqual({ call, privateHome: true, privateCodexHome: true });
+        }
+        expect(fs.existsSync(path.join(home, '.codex'))).toBe(false);
+      } finally { fs.rmSync(home, { recursive: true, force: true }); }
+    });
+  }
+});
diff --git a/test/codex-resume-flag-semantics.test.ts b/test/codex-resume-flag-semantics.test.ts
index 8f702ef2b..3db172290 100644
--- a/test/codex-resume-flag-semantics.test.ts
+++ b/test/codex-resume-flag-semantics.test.ts
@@ -12,11 +12,20 @@
  * (the periodic-tier eval runners) will exercise it.
  */
 
-import { describe, test, expect } from 'bun:test';
+import { afterAll, describe, test, expect } from 'bun:test';
 import { spawnSync } from 'child_process';
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
 
 const codexPath = spawnSync('which', ['codex'], { encoding: 'utf-8', timeout: 30_000 }).stdout.trim();
 const codexAvailable = codexPath.length > 0;
+// Every codex run writes $CODEX_HOME/tmp/arg0, so the smoke gets a private
+// HOME and CODEX_HOME and never touches the developer's real ~/.codex.
+const smokeHome = fs.mkdtempSync(path.join(os.tmpdir(), 'codex-resume-smoke-'));
+fs.mkdirSync(path.join(smokeHome, '.codex'));
+const smokeEnv = { ...process.env, HOME: smokeHome, CODEX_HOME: path.join(smokeHome, '.codex') };
+afterAll(() => fs.rmSync(smokeHome, { recursive: true, force: true }));
 
 describe.skipIf(!codexAvailable)(
   'codex exec resume — flag semantics (live CLI smoke; closes #1270 regex-only gap)',
@@ -26,6 +35,7 @@ describe.skipIf(!codexAvailable)(
         encoding: 'utf-8',
         stdio: ['ignore', 'pipe', 'pipe'],
         timeout: 10_000,
+        env: smokeEnv,
       });
       const helpText = (result.stdout || '') + '\n' + (result.stderr || '');
       // The /codex skill builds resume invocations with `-c 'sandbox_mode="read-only"'`.
@@ -39,6 +49,7 @@ describe.skipIf(!codexAvailable)(
         encoding: 'utf-8',
         stdio: ['ignore', 'pipe', 'pipe'],
         timeout: 10_000,
+        env: smokeEnv,
       });
       const helpText = (result.stdout || '') + '\n' + (result.stderr || '');
       // The whole point of #1270 was that `codex exec resume` rejects `-C <dir>`.