diff --git a/scripts/postinstall.js b/scripts/postinstall.js
index 43a99eef..e190c038 100755
--- a/scripts/postinstall.js
+++ b/scripts/postinstall.js
@@ -12,14 +12,24 @@ const os = require('os');
  * Runs when: npm install -g @kaitranntt/ccs
  * Idempotent: Safe to run multiple times (won't overwrite existing configs)
  * Cross-platform: Works on Unix, macOS, Windows
+ *
+ * Test isolation: Set CCS_HOME env var to redirect all operations to a test directory
  */
 
+/**
+ * Get the CCS home directory (respects CCS_HOME env var for test isolation)
+ * @returns {string} Home directory path
+ */
+function getCcsHome() {
+  return process.env.CCS_HOME || os.homedir();
+}
+
 /**
  * Validate created configuration files
  * @returns {object} { success: boolean, errors: string[], warnings: string[] }
  */
 function validateConfiguration() {
-  const homedir = os.homedir();
+  const homedir = getCcsHome();
   const errors = [];
   const warnings = [];
 
@@ -63,8 +73,8 @@ function validateConfiguration() {
 
 function createConfigFiles() {
   try {
-    // Get user home directory (cross-platform)
-    const homedir = os.homedir();
+    // Get user home directory (cross-platform, respects CCS_HOME for test isolation)
+    const homedir = getCcsHome();
     const ccsDir = path.join(homedir, '.ccs');
 
     // Create ~/.ccs/ directory if missing
@@ -106,30 +116,9 @@ function createConfigFiles() {
     }
     console.log('');
 
-    // Copy .claude/ directory from package to ~/.ccs/.claude/ (v4.1.1)
-    try {
-      const ClaudeDirInstaller = require('../dist/utils/claude-dir-installer').default;
-      const installer = new ClaudeDirInstaller();
-      const packageDir = path.join(__dirname, '..');
-      installer.install(packageDir);
-
-      // Clean up deprecated files (v4.3.2)
-      installer.cleanupDeprecated();
-    } catch (err) {
-      console.warn('[!] Failed to install .claude/ directory:', err.message);
-      console.warn('    CCS items may not be available');
-    }
-
-    // Install CCS items to ~/.claude/ (v4.1.0)
-    try {
-      const { ClaudeSymlinkManager } = require('../dist/utils/claude-symlink-manager');
-      const claudeSymlinkManager = new ClaudeSymlinkManager();
-      claudeSymlinkManager.install();
-    } catch (err) {
-      console.warn('[!] CCS item installation warning:', err.message);
-      console.warn('    Run "ccs sync" to retry');
-    }
-    console.log('');
+    // NOTE: .claude/ directory installation moved to "ccs sync" command
+    // Users can run "ccs sync" to install CCS commands/skills to ~/.claude/
+    // This gives users control over when to modify their Claude configuration
 
     // Create config.json if missing
     const configPath = path.join(ccsDir, 'config.json');
diff --git a/src/utils/config-manager.ts b/src/utils/config-manager.ts
index ecd25e2a..dff576ac 100644
--- a/src/utils/config-manager.ts
+++ b/src/utils/config-manager.ts
@@ -9,11 +9,27 @@ import { error } from './helpers';
 // const { ErrorManager } = require('./error-manager');
 // const RecoveryManager = require('./recovery-manager');
 
+/**
+ * Get the CCS home directory (respects CCS_HOME env var for test isolation)
+ * @returns Home directory path
+ */
+export function getCcsHome(): string {
+  return process.env.CCS_HOME || os.homedir();
+}
+
+/**
+ * Get the CCS directory path (~/.ccs)
+ * @returns Path to .ccs directory
+ */
+export function getCcsDir(): string {
+  return path.join(getCcsHome(), '.ccs');
+}
+
 /**
  * Get config file path
  */
 export function getConfigPath(): string {
-  return process.env.CCS_CONFIG || path.join(os.homedir(), '.ccs', 'config.json');
+  return process.env.CCS_CONFIG || path.join(getCcsHome(), '.ccs', 'config.json');
 }
 
 /**
diff --git a/tests/fixtures/test-environment.js b/tests/fixtures/test-environment.js
new file mode 100644
index 00000000..bd6d7554
--- /dev/null
+++ b/tests/fixtures/test-environment.js
@@ -0,0 +1,160 @@
+#!/usr/bin/env node
+'use strict';
+
+/**
+ * Test Environment Isolation
+ *
+ * Provides isolated ~/.ccs/ directory for tests to prevent
+ * interference with the user's actual CCS configuration.
+ *
+ * Usage:
+ *   const { createTestEnvironment } = require('../fixtures/test-environment');
+ *
+ *   describe('my tests', () => {
+ *     let testEnv;
+ *
+ *     before(() => {
+ *       testEnv = createTestEnvironment();
+ *     });
+ *
+ *     after(() => {
+ *       testEnv.cleanup();
+ *     });
+ *
+ *     it('test something', () => {
+ *       // Tests run with CCS_HOME pointing to temp directory
+ *       // Your test code here
+ *     });
+ *   });
+ */
+
+const fs = require('fs');
+const path = require('path');
+const os = require('os');
+
+/**
+ * Create an isolated test environment
+ * Sets CCS_HOME to a temporary directory and provides cleanup
+ *
+ * @returns {object} Test environment with paths and cleanup function
+ */
+function createTestEnvironment() {
+  // Create unique temp directory for this test run
+  const tempBase = path.join(os.tmpdir(), 'ccs-test');
+  const uniqueId = `${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
+  const testHome = path.join(tempBase, uniqueId);
+  const testCcsDir = path.join(testHome, '.ccs');
+
+  // Create directories
+  fs.mkdirSync(testCcsDir, { recursive: true });
+
+  // Store original environment
+  const originalHome = process.env.HOME;
+  const originalCcsHome = process.env.CCS_HOME;
+  const originalUserProfile = process.env.USERPROFILE;
+
+  // Set test environment - use CCS_HOME for isolation
+  process.env.CCS_HOME = testHome;
+
+  // Return environment object
+  return {
+    /** Path to the test home directory (like ~) */
+    testHome,
+
+    /** Path to the test .ccs directory (like ~/.ccs) */
+    ccsDir: testCcsDir,
+
+    /** Original HOME value for reference */
+    originalHome,
+
+    /**
+     * Get a path within the test CCS directory
+     * @param {...string} parts - Path segments
+     * @returns {string} Full path
+     */
+    getCcsPath(...parts) {
+      return path.join(testCcsDir, ...parts);
+    },
+
+    /**
+     * Create a file in the test CCS directory
+     * @param {string} relativePath - Path relative to .ccs/
+     * @param {string|object} content - File content (objects are JSON stringified)
+     */
+    createFile(relativePath, content) {
+      const fullPath = path.join(testCcsDir, relativePath);
+      const dir = path.dirname(fullPath);
+      if (!fs.existsSync(dir)) {
+        fs.mkdirSync(dir, { recursive: true });
+      }
+      const data = typeof content === 'object' ? JSON.stringify(content, null, 2) : content;
+      fs.writeFileSync(fullPath, data);
+    },
+
+    /**
+     * Read a file from the test CCS directory
+     * @param {string} relativePath - Path relative to .ccs/
+     * @param {boolean} [asJson=false] - Parse as JSON
+     * @returns {string|object} File content
+     */
+    readFile(relativePath, asJson = false) {
+      const fullPath = path.join(testCcsDir, relativePath);
+      const content = fs.readFileSync(fullPath, 'utf8');
+      return asJson ? JSON.parse(content) : content;
+    },
+
+    /**
+     * Check if a file exists in the test CCS directory
+     * @param {string} relativePath - Path relative to .ccs/
+     * @returns {boolean}
+     */
+    fileExists(relativePath) {
+      return fs.existsSync(path.join(testCcsDir, relativePath));
+    },
+
+    /**
+     * Clean up the test environment and restore original settings
+     */
+    cleanup() {
+      // Restore original environment
+      if (originalCcsHome !== undefined) {
+        process.env.CCS_HOME = originalCcsHome;
+      } else {
+        delete process.env.CCS_HOME;
+      }
+
+      // Clean up temp directory
+      try {
+        fs.rmSync(testHome, { recursive: true, force: true });
+      } catch (err) {
+        // Ignore cleanup errors
+        console.warn(`[test-environment] Cleanup warning: ${err.message}`);
+      }
+    }
+  };
+}
+
+/**
+ * Get the CCS home directory (respects CCS_HOME env var)
+ * This should be used instead of os.homedir() for CCS paths
+ *
+ * @returns {string} Home directory path
+ */
+function getCcsHome() {
+  return process.env.CCS_HOME || os.homedir();
+}
+
+/**
+ * Get the CCS directory path
+ *
+ * @returns {string} Path to .ccs directory
+ */
+function getCcsDir() {
+  return path.join(getCcsHome(), '.ccs');
+}
+
+module.exports = {
+  createTestEnvironment,
+  getCcsHome,
+  getCcsDir
+};
diff --git a/tests/npm/cli.test.js b/tests/npm/cli.test.js
index a98083e3..47d6f2f1 100644
--- a/tests/npm/cli.test.js
+++ b/tests/npm/cli.test.js
@@ -1,28 +1,47 @@
 const assert = require('assert');
 const { execSync } = require('child_process');
 const path = require('path');
-const fs = require('fs');
-const os = require('os');
+const { createTestEnvironment } = require('../fixtures/test-environment');
 
 describe('npm CLI', () => {
   const ccsPath = path.join(__dirname, '..', '..', 'dist', 'ccs.js');
-  const ccsDir = path.join(os.homedir(), '.ccs');
-  const configPath = path.join(ccsDir, 'config.json');
+  let testEnv;
+  let testCcsHome;
 
   before(() => {
-    // Ensure CCS is installed and configured
-    if (!fs.existsSync(configPath)) {
-      const postinstallScript = path.join(__dirname, '..', '..', 'scripts', 'postinstall.js');
-      execSync(`node "${postinstallScript}"`, { stdio: 'ignore' });
+    // Create isolated test environment
+    testEnv = createTestEnvironment();
+    testCcsHome = testEnv.testHome;
+
+    // Run postinstall to create config in test environment
+    const postinstallScript = path.join(__dirname, '..', '..', 'scripts', 'postinstall.js');
+    execSync(`node "${postinstallScript}"`, {
+      stdio: 'ignore',
+      env: { ...process.env, CCS_HOME: testCcsHome }
+    });
+  });
+
+  after(() => {
+    // Clean up test environment
+    if (testEnv) {
+      testEnv.cleanup();
     }
   });
 
+  // Helper to run CLI with test environment
+  function runCli(args, options = {}) {
+    return execSync(`node "${ccsPath}" ${args}`, {
+      ...options,
+      env: { ...process.env, CCS_HOME: testCcsHome }
+    });
+  }
+
   describe('Argument parsing', () => {
     it('handles flag -c without profile error', function() {
       this.timeout(5000);
 
       try {
-        execSync(`node "${ccsPath}" -c`, { stdio: 'pipe' });
+        runCli('-c', { stdio: 'pipe' });
       } catch (e) {
         const output = e.stderr?.toString() || e.stdout?.toString() || '';
         // Should NOT show "Profile '-c' not found" error
@@ -34,7 +53,7 @@ describe('npm CLI', () => {
       this.timeout(5000);
 
       try {
-        execSync(`node "${ccsPath}" --verbose`, { stdio: 'pipe' });
+        runCli('--verbose', { stdio: 'pipe' });
       } catch (e) {
         const output = e.stderr?.toString() || e.stdout?.toString() || '';
         assert(!output.includes("Profile '--verbose' not found"), 'Should not treat --verbose as profile');
@@ -45,7 +64,7 @@ describe('npm CLI', () => {
       this.timeout(10000);
 
       try {
-        execSync(`node "${ccsPath}" -p "test prompt"`, { stdio: 'pipe', timeout: 8000 });
+        runCli('-p "test prompt"', { stdio: 'pipe', timeout: 8000 });
       } catch (e) {
         const output = e.stderr?.toString() || e.stdout?.toString() || '';
         assert(!output.includes("Profile '-p' not found"), 'Should not treat -p as profile');
@@ -56,7 +75,7 @@ describe('npm CLI', () => {
       this.timeout(5000);
 
       try {
-        execSync(`node "${ccsPath}" -c --verbose`, { stdio: 'pipe' });
+        runCli('-c --verbose', { stdio: 'pipe' });
       } catch (e) {
         const output = e.stderr?.toString() || e.stdout?.toString() || '';
         assert(!output.includes("Profile '-c' not found"), 'Should not treat flags as profiles');
@@ -70,7 +89,7 @@ describe('npm CLI', () => {
       this.timeout(5000);
 
       try {
-        execSync(`node "${ccsPath}" glm --help`, { stdio: 'pipe' });
+        runCli('glm --help', { stdio: 'pipe' });
       } catch (e) {
         const output = e.stderr?.toString() || '';
         assert(!output.includes("Profile 'glm' not found"), 'GLM profile should exist');
@@ -81,7 +100,7 @@ describe('npm CLI', () => {
       this.timeout(5000);
 
       try {
-        execSync(`node "${ccsPath}" invalid-profile-name`, { stdio: 'pipe' });
+        runCli('invalid-profile-name', { stdio: 'pipe' });
         assert(false, 'Should have thrown an error for invalid profile');
       } catch (e) {
         const output = e.stderr?.toString() || e.stdout?.toString() || '';
@@ -93,7 +112,7 @@ describe('npm CLI', () => {
       this.timeout(5000);
 
       try {
-        execSync(`node "${ccsPath}" glm -c`, { stdio: 'pipe' });
+        runCli('glm -c', { stdio: 'pipe' });
       } catch (e) {
         const output = e.stderr?.toString() || '';
         assert(!output.includes("Profile 'glm' not found"), 'GLM profile should exist');
@@ -106,28 +125,28 @@ describe('npm CLI', () => {
     it('shows version with --version flag', function() {
       this.timeout(5000);
 
-      const output = execSync(`node "${ccsPath}" --version`, { encoding: 'utf8' });
+      const output = runCli('--version', { encoding: 'utf8' });
       assert(/\d+\.\d+\.\d+/.test(output), 'Should show version number');
     });
 
     it('shows version with -v flag', function() {
       this.timeout(5000);
 
-      const output = execSync(`node "${ccsPath}" -v`, { encoding: 'utf8' });
+      const output = runCli('-v', { encoding: 'utf8' });
       assert(/\d+\.\d+\.\d+/.test(output), 'Should show version number');
     });
 
     it('shows help with --help flag', function() {
       this.timeout(5000);
 
-      const output = execSync(`node "${ccsPath}" --help`, { encoding: 'utf8' });
+      const output = runCli('--help', { encoding: 'utf8' });
       assert(/usage|help|options/i.test(output), 'Should show help information');
     });
 
     it('shows help with -h flag', function() {
       this.timeout(5000);
 
-      const output = execSync(`node "${ccsPath}" -h`, { encoding: 'utf8' });
+      const output = runCli('-h', { encoding: 'utf8' });
       assert(/usage|help|options/i.test(output), 'Should show help information');
     });
   });
@@ -137,7 +156,7 @@ describe('npm CLI', () => {
       this.timeout(5000);
 
       try {
-        execSync(`node "${ccsPath}"`, { stdio: 'pipe' });
+        runCli('', { stdio: 'pipe' });
       } catch (e) {
         // Should either succeed or fail gracefully with a helpful error
         const output = e.stderr?.toString() || e.stdout?.toString() || '';
@@ -150,7 +169,7 @@ describe('npm CLI', () => {
 
       const longArg = 'a'.repeat(1000);
       try {
-        execSync(`node "${ccsPath}" "${longArg}"`, { stdio: 'pipe' });
+        runCli(`"${longArg}"`, { stdio: 'pipe' });
       } catch (e) {
         // Should handle gracefully, not crash
         const output = e.stderr?.toString() || e.stdout?.toString() || '';
@@ -158,4 +177,4 @@ describe('npm CLI', () => {
       }
     });
   });
-});
\ No newline at end of file
+});
diff --git a/tests/npm/postinstall.test.js b/tests/npm/postinstall.test.js
index 874a7074..438a0870 100644
--- a/tests/npm/postinstall.test.js
+++ b/tests/npm/postinstall.test.js
@@ -1,53 +1,56 @@
 const assert = require('assert');
 const { execSync } = require('child_process');
-const fs = require('fs');
 const path = require('path');
-const os = require('os');
+const { createTestEnvironment } = require('../fixtures/test-environment');
 
 describe('npm postinstall', () => {
-  const ccsDir = path.join(os.homedir(), '.ccs');
-  const configPath = path.join(ccsDir, 'config.json');
-  const glmPath = path.join(ccsDir, 'glm.settings.json');
+  let testEnv;
   const postinstallScript = path.join(__dirname, '..', '..', 'scripts', 'postinstall.js');
 
   beforeEach(() => {
-    // Clean slate before each test
-    if (fs.existsSync(ccsDir)) {
-      fs.rmSync(ccsDir, { recursive: true, force: true });
-    }
+    // Create isolated test environment for each test
+    testEnv = createTestEnvironment();
   });
 
-  after(() => {
-    // Cleanup after all tests
-    if (fs.existsSync(ccsDir)) {
-      fs.rmSync(ccsDir, { recursive: true, force: true });
+  afterEach(() => {
+    // Clean up test environment
+    if (testEnv) {
+      testEnv.cleanup();
     }
   });
 
   it('creates config.json', () => {
-    execSync(`node "${postinstallScript}"`, { stdio: 'ignore' });
+    execSync(`node "${postinstallScript}"`, {
+      stdio: 'ignore',
+      env: { ...process.env, CCS_HOME: testEnv.testHome }
+    });
 
-    assert(fs.existsSync(configPath), 'config.json should be created');
+    assert(testEnv.fileExists('config.json'), 'config.json should be created');
 
-    const config = JSON.parse(fs.readFileSync(configPath, 'utf8'));
+    const config = testEnv.readFile('config.json', true);
     assert(config.profiles, 'config.json should have profiles');
     assert(typeof config.profiles === 'object', 'profiles should be an object');
   });
 
   it('creates glm.settings.json', () => {
-    execSync(`node "${postinstallScript}"`, { stdio: 'ignore' });
+    execSync(`node "${postinstallScript}"`, {
+      stdio: 'ignore',
+      env: { ...process.env, CCS_HOME: testEnv.testHome }
+    });
 
-    assert(fs.existsSync(glmPath), 'glm.settings.json should be created');
+    assert(testEnv.fileExists('glm.settings.json'), 'glm.settings.json should be created');
 
-    const glmSettings = JSON.parse(fs.readFileSync(glmPath, 'utf8'));
+    const glmSettings = testEnv.readFile('glm.settings.json', true);
     assert(glmSettings.env, 'glm.settings.json should have env section');
     assert(glmSettings.env.ANTHROPIC_MODEL, 'should have ANTHROPIC_MODEL set');
     assert.strictEqual(glmSettings.env.ANTHROPIC_MODEL, 'glm-4.6');
   });
 
   it('is idempotent', () => {
+    const env = { ...process.env, CCS_HOME: testEnv.testHome };
+
     // Run postinstall first time
-    execSync(`node "${postinstallScript}"`, { stdio: 'ignore' });
+    execSync(`node "${postinstallScript}"`, { stdio: 'ignore', env });
 
     // Create custom config
     const customConfig = {
@@ -56,19 +59,22 @@ describe('npm postinstall', () => {
         glm: '~/.ccs/glm.settings.json'
       }
     };
-    fs.writeFileSync(configPath, JSON.stringify(customConfig, null, 2));
+    testEnv.createFile('config.json', customConfig);
 
     // Run postinstall again
-    execSync(`node "${postinstallScript}"`, { stdio: 'ignore' });
+    execSync(`node "${postinstallScript}"`, { stdio: 'ignore', env });
 
     // Verify custom config preserved
-    const config = JSON.parse(fs.readFileSync(configPath, 'utf8'));
+    const config = testEnv.readFile('config.json', true);
     assert(config.profiles.custom, 'Custom profile should be preserved');
     assert.strictEqual(config.profiles.custom, '~/.custom.json');
   });
 
   it('uses ASCII symbols', () => {
-    const output = execSync(`node "${postinstallScript}"`, { encoding: 'utf8' });
+    const output = execSync(`node "${postinstallScript}"`, {
+      encoding: 'utf8',
+      env: { ...process.env, CCS_HOME: testEnv.testHome }
+    });
 
     // Check for ASCII symbols [OK], [!], [X], [i] - not emojis
     assert(/\[(OK|!|X|i)\]/.test(output), 'Should use ASCII symbols, not emojis');
@@ -80,23 +86,27 @@ describe('npm postinstall', () => {
 
   it('handles existing directory gracefully', () => {
     // Create directory manually first
-    fs.mkdirSync(ccsDir, { recursive: true });
-    fs.writeFileSync(path.join(ccsDir, 'existing.txt'), 'exists');
+    testEnv.createFile('existing.txt', 'exists');
 
     // Run postinstall
-    execSync(`node "${postinstallScript}"`, { stdio: 'ignore' });
+    execSync(`node "${postinstallScript}"`, {
+      stdio: 'ignore',
+      env: { ...process.env, CCS_HOME: testEnv.testHome }
+    });
 
     // Verify existing file still exists and new files are created
-    assert(fs.existsSync(path.join(ccsDir, 'existing.txt')), 'Existing files should be preserved');
-    assert(fs.existsSync(configPath), 'config.json should be created');
-    assert(fs.existsSync(glmPath), 'glm.settings.json should be created');
+    assert(testEnv.fileExists('existing.txt'), 'Existing files should be preserved');
+    assert(testEnv.fileExists('config.json'), 'config.json should be created');
+    assert(testEnv.fileExists('glm.settings.json'), 'glm.settings.json should be created');
   });
 
   it('does not create VERSION file', () => {
-    execSync(`node "${postinstallScript}"`, { stdio: 'ignore' });
+    execSync(`node "${postinstallScript}"`, {
+      stdio: 'ignore',
+      env: { ...process.env, CCS_HOME: testEnv.testHome }
+    });
 
-    const versionPath = path.join(ccsDir, 'VERSION');
     // The postinstall script doesn't create VERSION file (only native install does)
-    assert(!fs.existsSync(versionPath), 'VERSION file should NOT be created by npm postinstall');
+    assert(!testEnv.fileExists('VERSION'), 'VERSION file should NOT be created by npm postinstall');
   });
-});
\ No newline at end of file
+});