diff --git a/package.json b/package.json
index cd02e3746..4de0f9e75 100644
--- a/package.json
+++ b/package.json
@@ -40,7 +40,8 @@
     "lint:md": "markdownlint-cli2 \"**/*.md\"",
     "prepare": "command -v husky >/dev/null 2>&1 && husky || exit 0",
     "rebundle": "node tools/cli/bundlers/bundle-web.js rebundle",
-    "test": "npm run test:schemas && npm run test:refs && npm run test:install && npm run validate:schemas && npm run lint && npm run lint:md && npm run format:check",
+    "test": "npm run test:schemas && npm run test:refs && npm run test:install && npm run test:copilot && npm run validate:schemas && npm run lint && npm run lint:md && npm run format:check",
+    "test:copilot": "node test/test-github-copilot-installer.js",
     "test:coverage": "c8 --reporter=text --reporter=html npm run test:schemas",
     "test:install": "node test/test-installation-components.js",
     "test:refs": "node test/test-file-refs-csv.js",
diff --git a/test/test-github-copilot-installer.js b/test/test-github-copilot-installer.js
new file mode 100644
index 000000000..7db0af8fe
--- /dev/null
+++ b/test/test-github-copilot-installer.js
@@ -0,0 +1,238 @@
+/**
+ * GitHub Copilot Installer Tests
+ *
+ * Tests for the GitHubCopilotSetup class methods:
+ * - loadModuleConfig: module-aware config loading
+ * - createTechWriterPromptContent: BMM-only tech-writer handling
+ * - generateCopilotInstructions: selectedModules deduplication
+ *
+ * Usage: node test/test-github-copilot-installer.js
+ */
+
+const path = require('node:path');
+const fs = require('fs-extra');
+const { GitHubCopilotSetup } = require('../tools/cli/installers/lib/ide/github-copilot');
+
+// ANSI colors
+const colors = {
+  reset: '\u001B[0m',
+  green: '\u001B[32m',
+  red: '\u001B[31m',
+  yellow: '\u001B[33m',
+  cyan: '\u001B[36m',
+  dim: '\u001B[2m',
+};
+
+let passed = 0;
+let failed = 0;
+
+/**
+ * Test helper: Assert condition
+ */
+function assert(condition, testName, errorMessage = '') {
+  if (condition) {
+    console.log(`${colors.green}✓${colors.reset} ${testName}`);
+    passed++;
+  } else {
+    console.log(`${colors.red}✗${colors.reset} ${testName}`);
+    if (errorMessage) {
+      console.log(`  ${colors.dim}${errorMessage}${colors.reset}`);
+    }
+    failed++;
+  }
+}
+
+/**
+ * Test Suite
+ */
+async function runTests() {
+  console.log(`${colors.cyan}========================================`);
+  console.log('GitHub Copilot Installer Tests');
+  console.log(`========================================${colors.reset}\n`);
+
+  const tempDir = path.join(__dirname, 'temp-copilot-test');
+
+  try {
+    // Clean up any leftover temp directory
+    await fs.remove(tempDir);
+    await fs.ensureDir(tempDir);
+
+    const installer = new GitHubCopilotSetup();
+
+    // ============================================================
+    // Test Suite 1: loadModuleConfig
+    // ============================================================
+    console.log(`${colors.yellow}Test Suite 1: loadModuleConfig${colors.reset}\n`);
+
+    // Create mock bmad directory structure with multiple modules
+    const bmadDir = path.join(tempDir, '_bmad');
+    await fs.ensureDir(path.join(bmadDir, 'core'));
+    await fs.ensureDir(path.join(bmadDir, 'bmm'));
+    await fs.ensureDir(path.join(bmadDir, 'custom-module'));
+
+    // Create config files for each module
+    await fs.writeFile(path.join(bmadDir, 'core', 'config.yaml'), 'project_name: Core Project\nuser_name: CoreUser\n');
+    await fs.writeFile(path.join(bmadDir, 'bmm', 'config.yaml'), 'project_name: BMM Project\nuser_name: BmmUser\n');
+    await fs.writeFile(path.join(bmadDir, 'custom-module', 'config.yaml'), 'project_name: Custom Project\nuser_name: CustomUser\n');
+
+    // Test 1a: Load config with only core module (default)
+    const coreConfig = await installer.loadModuleConfig(bmadDir, ['core']);
+    assert(
+      coreConfig.project_name === 'Core Project',
+      'loadModuleConfig loads core config when only core installed',
+      `Got: ${coreConfig.project_name}`,
+    );
+
+    // Test 1b: Load config with bmm module (should prefer bmm over core)
+    const bmmConfig = await installer.loadModuleConfig(bmadDir, ['bmm', 'core']);
+    assert(bmmConfig.project_name === 'BMM Project', 'loadModuleConfig prefers bmm config over core', `Got: ${bmmConfig.project_name}`);
+
+    // Test 1c: Load config with custom module (should prefer custom over core)
+    const customConfig = await installer.loadModuleConfig(bmadDir, ['custom-module', 'core']);
+    assert(
+      customConfig.project_name === 'Custom Project',
+      'loadModuleConfig prefers custom module config over core',
+      `Got: ${customConfig.project_name}`,
+    );
+
+    // Test 1d: Load config with multiple non-core modules (first wins)
+    const multiConfig = await installer.loadModuleConfig(bmadDir, ['bmm', 'custom-module', 'core']);
+    assert(
+      multiConfig.project_name === 'BMM Project',
+      'loadModuleConfig uses first non-core module config',
+      `Got: ${multiConfig.project_name}`,
+    );
+
+    // Test 1e: Empty modules list uses default (core)
+    const defaultConfig = await installer.loadModuleConfig(bmadDir);
+    assert(
+      defaultConfig.project_name === 'Core Project',
+      'loadModuleConfig defaults to core when no modules specified',
+      `Got: ${defaultConfig.project_name}`,
+    );
+
+    // Test 1f: Non-existent module falls back to core
+    const fallbackConfig = await installer.loadModuleConfig(bmadDir, ['nonexistent', 'core']);
+    assert(
+      fallbackConfig.project_name === 'Core Project',
+      'loadModuleConfig falls back to core for non-existent modules',
+      `Got: ${fallbackConfig.project_name}`,
+    );
+
+    console.log('');
+
+    // ============================================================
+    // Test Suite 2: createTechWriterPromptContent (BMM-only)
+    // ============================================================
+    console.log(`${colors.yellow}Test Suite 2: createTechWriterPromptContent (BMM-only)${colors.reset}\n`);
+
+    // Test 2a: BMM tech-writer entry should generate content
+    const bmmTechWriterEntry = {
+      'agent-name': 'tech-writer',
+      module: 'bmm',
+      name: 'Write Document',
+    };
+    const bmmResult = installer.createTechWriterPromptContent(bmmTechWriterEntry);
+    assert(
+      bmmResult !== null && bmmResult.fileName === 'bmad-bmm-write-document',
+      'createTechWriterPromptContent generates content for BMM tech-writer',
+      `Got: ${bmmResult ? bmmResult.fileName : 'null'}`,
+    );
+
+    // Test 2b: Non-BMM tech-writer entry should return null
+    const customTechWriterEntry = {
+      'agent-name': 'tech-writer',
+      module: 'custom-module',
+      name: 'Write Document',
+    };
+    const customResult = installer.createTechWriterPromptContent(customTechWriterEntry);
+    assert(customResult === null, 'createTechWriterPromptContent returns null for non-BMM tech-writer', `Got: ${customResult}`);
+
+    // Test 2c: Core tech-writer entry should return null
+    const coreTechWriterEntry = {
+      'agent-name': 'tech-writer',
+      module: 'core',
+      name: 'Write Document',
+    };
+    const coreResult = installer.createTechWriterPromptContent(coreTechWriterEntry);
+    assert(coreResult === null, 'createTechWriterPromptContent returns null for core tech-writer', `Got: ${coreResult}`);
+
+    // Test 2d: Non-tech-writer BMM entry should return null
+    const nonTechWriterEntry = {
+      'agent-name': 'pm',
+      module: 'bmm',
+      name: 'Write Document',
+    };
+    const nonTechResult = installer.createTechWriterPromptContent(nonTechWriterEntry);
+    assert(nonTechResult === null, 'createTechWriterPromptContent returns null for non-tech-writer agents', `Got: ${nonTechResult}`);
+
+    // Test 2e: Unknown tech-writer command should return null
+    const unknownCmdEntry = {
+      'agent-name': 'tech-writer',
+      module: 'bmm',
+      name: 'Unknown Command',
+    };
+    const unknownResult = installer.createTechWriterPromptContent(unknownCmdEntry);
+    assert(unknownResult === null, 'createTechWriterPromptContent returns null for unknown commands', `Got: ${unknownResult}`);
+
+    console.log('');
+
+    // ============================================================
+    // Test Suite 3: selectedModules deduplication
+    // ============================================================
+    console.log(`${colors.yellow}Test Suite 3: selectedModules deduplication${colors.reset}\n`);
+
+    // We can't easily test generateCopilotInstructions directly without mocking,
+    // but we can verify the deduplication logic pattern
+    const testDedupe = (modules) => {
+      const installedModules = modules.length > 0 ? [...new Set(modules)] : ['core'];
+      return installedModules;
+    };
+
+    // Test 3a: Duplicate modules should be deduplicated
+    const dupeResult = testDedupe(['bmm', 'core', 'bmm', 'custom', 'core', 'custom']);
+    assert(
+      dupeResult.length === 3 && dupeResult.includes('bmm') && dupeResult.includes('core') && dupeResult.includes('custom'),
+      'Deduplication removes duplicate modules',
+      `Got: ${JSON.stringify(dupeResult)}`,
+    );
+
+    // Test 3b: Empty array defaults to core
+    const emptyResult = testDedupe([]);
+    assert(
+      emptyResult.length === 1 && emptyResult[0] === 'core',
+      'Empty modules array defaults to core',
+      `Got: ${JSON.stringify(emptyResult)}`,
+    );
+
+    // Test 3c: Order is preserved after deduplication (first occurrence wins)
+    const orderResult = testDedupe(['custom', 'bmm', 'custom', 'bmm']);
+    assert(
+      orderResult[0] === 'custom' && orderResult[1] === 'bmm',
+      'Deduplication preserves order (first occurrence)',
+      `Got: ${JSON.stringify(orderResult)}`,
+    );
+  } finally {
+    // Cleanup
+    await fs.remove(tempDir);
+  }
+
+  // Print summary
+  console.log(`${colors.cyan}========================================`);
+  console.log('Test Results:');
+  console.log(`  Passed: ${passed}`);
+  console.log(`  Failed: ${failed}`);
+  console.log(`========================================${colors.reset}\n`);
+
+  if (failed > 0) {
+    console.log(`${colors.red}Some tests failed!${colors.reset}`);
+    process.exit(1);
+  } else {
+    console.log(`${colors.green}✨ All GitHub Copilot installer tests passed!${colors.reset}`);
+  }
+}
+
+runTests().catch((error) => {
+  console.error(`${colors.red}Test runner error:${colors.reset}`, error);
+  process.exit(1);
+});
diff --git a/tools/cli/installers/lib/ide/github-copilot.js b/tools/cli/installers/lib/ide/github-copilot.js
index 5862eb758..7379eade6 100644
--- a/tools/cli/installers/lib/ide/github-copilot.js
+++ b/tools/cli/installers/lib/ide/github-copilot.js
@@ -325,11 +325,13 @@ ${body}
 
   /**
    * Create prompt content for tech-writer agent-only commands (Pattern C)
+   * Tech-writer is BMM-specific - these commands only work with the BMM module.
    * @param {Object} entry - bmad-help.csv row
    * @returns {Object|null} { fileName, content } or null if not a tech-writer command
    */
   createTechWriterPromptContent(entry) {
-    if (entry['agent-name'] !== 'tech-writer') return null;
+    // Tech-writer is BMM-specific - only process entries from the bmm module
+    if (entry['agent-name'] !== 'tech-writer' || entry.module !== 'bmm') return null;
 
     const techWriterCommands = {
       'Write Document': { code: 'WD', file: 'bmad-bmm-write-document', description: 'Write document' },
@@ -403,11 +405,11 @@ tools: ${toolsStr}
    * @param {Map} agentManifest - Agent manifest data
    */
   async generateCopilotInstructions(projectDir, bmadDir, agentManifest, options = {}) {
-    const configVars = await this.loadModuleConfig(bmadDir);
-
     // Determine installed modules (excluding internal directories)
     const selectedModules = options.selectedModules || [];
-    const installedModules = selectedModules.length > 0 ? selectedModules : ['core'];
+    // Deduplicate selectedModules to prevent duplicate paths in generated markdown
+    const installedModules = selectedModules.length > 0 ? [...new Set(selectedModules)] : ['core'];
+    const configVars = await this.loadModuleConfig(bmadDir, installedModules);
     // Filter to only non-core modules for display (core is always listed separately)
     const nonCoreModules = installedModules.filter((m) => m !== 'core');
 
@@ -466,9 +468,6 @@ tools: ${toolsStr}
       moduleConfigLine = `- **Module configuration**: (no non-core modules installed)`;
     }
 
-    // Determine primary module for config loading instruction
-    const primaryModule = nonCoreModules.length > 0 ? nonCoreModules[0] : 'core';
-
     const bmadSection = `# BMAD Method — Project Instructions
 
 ## Project Configuration
@@ -546,13 +545,15 @@ Type \`/bmad-\` in Copilot Chat to see all available BMAD workflows and agent ac
   /**
    * Load module config.yaml for template variables
    * @param {string} bmadDir - BMAD installation directory
+   * @param {string[]} installedModules - List of installed modules to check for config
    * @returns {Object} Config variables
    */
-  async loadModuleConfig(bmadDir) {
-    const bmmConfigPath = path.join(bmadDir, 'bmm', 'config.yaml');
-    const coreConfigPath = path.join(bmadDir, 'core', 'config.yaml');
+  async loadModuleConfig(bmadDir, installedModules = ['core']) {
+    // Build config paths from installed modules (non-core first, then core as fallback)
+    const nonCoreModules = installedModules.filter((m) => m !== 'core');
+    const configPaths = [...nonCoreModules.map((m) => path.join(bmadDir, m, 'config.yaml')), path.join(bmadDir, 'core', 'config.yaml')];
 
-    for (const configPath of [bmmConfigPath, coreConfigPath]) {
+    for (const configPath of configPaths) {
       if (await fs.pathExists(configPath)) {
         try {
           const content = await fs.readFile(configPath, 'utf8');