diff --git a/scripts/install-guided.js b/scripts/install-guided.js
index 4fa27525d..08a1a15e6 100644
--- a/scripts/install-guided.js
+++ b/scripts/install-guided.js
@@ -106,7 +106,11 @@ function parseArgs(argv) {
   if (options.allHarnesses && options.harnesses.length > 0) {
     throw new Error('--all-harnesses and --harness are mutually exclusive.');
   }
-  return options;
+  const dryRunEnv = process.env.ECC_DRY_RUN;
+  if (dryRunEnv !== undefined && dryRunEnv !== '0' && dryRunEnv !== '1') {
+    throw new Error('ECC_DRY_RUN must be "1" or "0" when set');
+  }
+  return { ...options, dryRun: options.dryRun || dryRunEnv === '1' };
 }
 
 function choicesText(values) {
diff --git a/tests/scripts/install-guided-global-dry-run.test.js b/tests/scripts/install-guided-global-dry-run.test.js
new file mode 100644
index 000000000..40e6ae8fa
--- /dev/null
+++ b/tests/scripts/install-guided-global-dry-run.test.js
@@ -0,0 +1,47 @@
+'use strict';
+
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const os = require('node:os');
+const path = require('node:path');
+const { spawnSync } = require('node:child_process');
+const test = require('node:test');
+
+const repoRoot = path.resolve(__dirname, '../..');
+
+for (const entry of ['install-guided.js', 'install-apply.js', 'ecc.js']) {
+  test(`global dry-run protects the actual ${entry} guided workflow`, () => {
+    const root = fs.mkdtempSync(path.join(os.tmpdir(), 'ecc-guided-global-preview-'));
+    try {
+      const home = path.join(root, 'home');
+      const project = path.join(root, 'project');
+      fs.mkdirSync(home);
+      fs.mkdirSync(project);
+      const args = entry === 'ecc.js' ? ['--dry-run', 'install', '--guided']
+        : entry === 'install-apply.js' ? ['--guided'] : [];
+      const child = spawnSync(process.execPath, [path.join(repoRoot, 'scripts', entry),
+        ...args, '--harness', 'kimi', '--profile', 'minimal', '--yes', '--json'], {
+        cwd: project, encoding: 'utf8', timeout: 30000, maxBuffer: 16 * 1024 * 1024,
+        env: { ...process.env, HOME: home, USERPROFILE: home,
+          CLAUDE_CONFIG_DIR: path.join(home, '.claude'), ECC_DRY_RUN: '1' },
+      });
+      assert.equal(child.status, 0, child.stderr);
+      const payload = JSON.parse(child.stdout);
+      assert.equal(payload.dryRun, true);
+      assert.equal(payload.plan.request.dryRun, true);
+      assert.deepEqual(fs.readdirSync(home), []);
+      assert.deepEqual(fs.readdirSync(project), []);
+    } finally {
+      fs.rmSync(root, { recursive: true, force: true });
+    }
+  });
+}
+
+test('invalid global dry-run input is rejected before guided planning', () => {
+  const child = spawnSync(process.execPath, [path.join(repoRoot, 'scripts/install-guided.js'),
+    '--harness', 'kimi', '--yes', '--json'], {
+    encoding: 'utf8', env: { ...process.env, ECC_DRY_RUN: 'yes' },
+  });
+  assert.equal(child.status, 1);
+  assert.match(JSON.parse(child.stderr).error.message, /ECC_DRY_RUN must be "1" or "0"/);
+});