diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 80804be6..ff145fda 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -48,6 +48,9 @@ jobs:
           node-version: 20
           cache: npm
 
+      - name: Test postinstall helpers
+        run: node --test test/postinstall.test.js
+
       - uses: actions/setup-python@v5
         with:
           python-version: '3.12'
diff --git a/scripts/postinstall.js b/scripts/postinstall.js
index 6b46dfda..32c1db0f 100644
--- a/scripts/postinstall.js
+++ b/scripts/postinstall.js
@@ -1,31 +1,33 @@
 #!/usr/bin/env node
-const { execSync } = require('child_process');
+const { execSync, execFileSync } = require('child_process');
 const path = require('path');
 const fs = require('fs');
 
-// Install native dependencies for Electron
-try {
-  execSync('npx electron-builder install-app-deps', { stdio: 'inherit' });
-} catch (err) {
-  console.error('electron-builder install-app-deps failed:', err.message);
-  // Fallback: rebuild only better-sqlite3 for Electron (node-pty uses prebuilds)
-  console.log('Attempting fallback: rebuilding better-sqlite3 for Electron...');
+if (require.main === module) {
+  // Install native dependencies for Electron
   try {
-    execSync('npx @electron/rebuild -f -m . -o better-sqlite3', { stdio: 'inherit' });
-    console.log('Fallback rebuild succeeded.');
-  } catch (err2) {
-    console.error('Fallback rebuild also failed:', err2.message);
+    execSync('npx electron-builder install-app-deps', { stdio: 'inherit' });
+  } catch (err) {
+    console.error('electron-builder install-app-deps failed:', err.message);
+    // Fallback: rebuild only better-sqlite3 for Electron (node-pty uses prebuilds)
+    console.log('Attempting fallback: rebuilding better-sqlite3 for Electron...');
+    try {
+      execSync('npx @electron/rebuild -f -m . -o better-sqlite3', { stdio: 'inherit' });
+      console.log('Fallback rebuild succeeded.');
+    } catch (err2) {
+      console.error('Fallback rebuild also failed:', err2.message);
+    }
   }
 }
 
 // macOS/Linux: ad-hoc codesign native modules & fix node-pty permissions
-if (process.platform !== 'win32') {
+if (require.main === module && process.platform !== 'win32') {
   // Ad-hoc codesign all .node files so macOS doesn't block them
   try {
     const nodeModules = path.join(__dirname, '..', 'node_modules');
     findFiles(nodeModules, '.node').forEach(file => {
       try {
-        execSync(`codesign --sign - --force "${file}"`, { stdio: 'ignore' });
+        codesignFile(file);
       } catch {}
     });
   } catch {}
@@ -58,3 +60,9 @@ function findFiles(dir, suffix) {
   } catch {}
   return results;
 }
+
+function codesignFile(file, sign = execFileSync) {
+  sign('codesign', ['--sign', '-', '--force', file], { stdio: 'ignore' });
+}
+
+module.exports = { findFiles, codesignFile };
diff --git a/test/postinstall.test.js b/test/postinstall.test.js
new file mode 100644
index 00000000..bf39bc9c
--- /dev/null
+++ b/test/postinstall.test.js
@@ -0,0 +1,63 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const os = require('node:os');
+const path = require('node:path');
+
+const { findFiles, codesignFile } = require('../scripts/postinstall');
+
+const SPECIAL_NAMES = ['some file.node', 'some"file.node', 'native\\addon.node'];
+
+function withTempDir(fn) {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'postinstall-test-'));
+  try {
+    return fn(dir);
+  } finally {
+    fs.rmSync(dir, { recursive: true, force: true });
+  }
+}
+
+for (const name of SPECIAL_NAMES) {
+  test(`findFiles returns the exact, unmangled path for filename: ${name}`, {
+    // Quotes are invalid and backslashes are path separators on Windows.
+    skip: process.platform === 'win32' && /["\\]/.test(name),
+  }, () => {
+    withTempDir(dir => {
+      const expected = path.join(dir, name);
+      fs.writeFileSync(expected, '');
+      const results = findFiles(dir, '.node');
+      assert.deepEqual(results, [expected]);
+      // The regressed behavior stripped \\ and / from the name, breaking the path.
+      assert.ok(fs.existsSync(results[0]));
+    });
+  });
+}
+
+test('findFiles descends into directories whose name contains a backslash', {
+  skip: process.platform === 'win32',
+}, () => {
+  withTempDir(dir => {
+    const subdir = path.join(dir, 'sub\\dir');
+    fs.mkdirSync(subdir);
+    const expected = path.join(subdir, 'addon.node');
+    fs.writeFileSync(expected, '');
+    const results = findFiles(dir, '.node');
+    assert.deepEqual(results, [expected]);
+  });
+});
+
+for (const name of SPECIAL_NAMES) {
+  test(`codesignFile passes filename unchanged to the signer for: ${name}`, () => {
+    // A stubbed signer only needs a path string, not a real filesystem entry.
+    const file = path.join(os.tmpdir(), name);
+    const calls = [];
+    const stubSign = (...args) => calls.push(args);
+    codesignFile(file, stubSign);
+    assert.equal(calls.length, 1);
+    assert.deepEqual(calls[0], [
+      'codesign',
+      ['--sign', '-', '--force', file],
+      { stdio: 'ignore' },
+    ]);
+  });
+}