fix(install): accept UTF-8 BOM in install configs

scripts/lib/install/config.js

@@ -10,7 +10,9 @@ let cachedValidator = null;
 
 function readJson(filePath, label) {
   try {
-    return JSON.parse(fs.readFileSync(filePath, 'utf8'));
+    // Windows PowerShell 5.1 writes a BOM with Set-Content -Encoding UTF8.
+    const content = fs.readFileSync(filePath, 'utf8').replace(/^\uFEFF/, '');
+    return JSON.parse(content);
   } catch (error) {
     throw new Error(`Invalid JSON in ${label}: ${error.message}`);
   }

tests/lib/install-config.test.js

@@ -106,6 +106,63 @@ function runTests() {
     }
   })) passed++; else failed++;
 
+  if (test('loads a UTF-8 BOM config without changing its values or source bytes', () => {
+    const cwd = createTempDir('install-config-');
+
+    try {
+      const configPath = path.join(cwd, 'ecc-install.json');
+      const value = { version: 1, target: 'cursor', modules: ['rules-core'] };
+      writeJson(configPath, value);
+      const expected = loadInstallConfig(configPath);
+      const content = `\uFEFF${JSON.stringify(value, null, 2).replace(/\n/g, '\r\n')}\r\n`;
+      fs.writeFileSync(configPath, content, 'utf8');
+
+      assert.deepStrictEqual(loadInstallConfig(configPath), expected);
+      assert.strictEqual(fs.readFileSync(configPath, 'utf8'), content);
+    } finally {
+      cleanup(cwd);
+    }
+  })) passed++; else failed++;
+
+  if (test('preserves BOM characters inside JSON string values', () => {
+    const cwd = createTempDir('install-config-');
+
+    try {
+      const configPath = path.join(cwd, 'ecc-install.json');
+      const options = { note: 'custom\uFEFFvalue' };
+      fs.writeFileSync(configPath, `\uFEFF${JSON.stringify({ version: 1, options })}`, 'utf8');
+      assert.deepStrictEqual(loadInstallConfig(configPath).options, options);
+    } finally {
+      cleanup(cwd);
+    }
+  })) passed++; else failed++;
+
+  if (test('still rejects malformed JSON and misplaced BOM characters', () => {
+    const cwd = createTempDir('install-config-');
+
+    try {
+      const configPath = path.join(cwd, 'ecc-install.json');
+      for (const content of ['\uFEFF{', ' \uFEFF{"version":1}', '\uFEFF\uFEFF{"version":1}']) {
+        fs.writeFileSync(configPath, content, 'utf8');
+        assert.throws(() => loadInstallConfig(configPath), /Invalid JSON in ecc-install.json/);
+      }
+    } finally {
+      cleanup(cwd);
+    }
+  })) passed++; else failed++;
+
+  if (test('validates the schema after reading a UTF-8 BOM config', () => {
+    const cwd = createTempDir('install-config-');
+
+    try {
+      const configPath = path.join(cwd, 'ecc-install.json');
+      fs.writeFileSync(configPath, '\uFEFF{"version":2,"target":"ghost-target"}', 'utf8');
+      assert.throws(() => loadInstallConfig(configPath), /Invalid install config/);
+    } finally {
+      cleanup(cwd);
+    }
+  })) passed++; else failed++;
+
   if (test('rejects invalid config schema values', () => {
     const cwd = createTempDir('install-config-');
 

tests/scripts/install-apply.test.js

@@ -1487,6 +1487,29 @@ function runTests() {
     }
   })) passed++; else failed++;
 
+  for (const explicitConfig of [true, false]) {
+    if (test(`installs from a UTF-8 BOM config (${explicitConfig ? '--config' : 'auto-detected'})`, () => {
+      const homeDir = createTempDir('install-apply-bom-home-');
+      const projectDir = createTempDir('install-apply-bom-project-');
+      const configPath = path.join(projectDir, 'ecc-install.json');
+      const content = '\uFEFF{\r\n  "version": 1,\r\n  "target": "cursor",\r\n  "modules": ["rules-core"]\r\n}\r\n';
+
+      try {
+        fs.writeFileSync(configPath, content, 'utf8');
+        const args = explicitConfig ? ['--config', configPath] : [];
+        const result = run(args, { cwd: projectDir, homeDir });
+        assert.strictEqual(result.code, 0, result.stderr);
+        assert.ok(fs.existsSync(path.join(projectDir, '.cursor', 'rules', 'common-coding-style.mdc')));
+        const state = readJson(path.join(projectDir, '.cursor', 'ecc-install-state.json'));
+        assert.deepStrictEqual(state.request.modules, ['rules-core']);
+        assert.strictEqual(fs.readFileSync(configPath, 'utf8'), content);
+      } finally {
+        cleanup(homeDir);
+        cleanup(projectDir);
+      }
+    })) passed++; else failed++;
+  }
+
   if (test('preserves legacy language installs when a project config is present', () => {
     const homeDir = createTempDir('install-apply-home-');
     const projectDir = createTempDir('install-apply-project-');