diff --git a/.github/workflows/dev.yml b/.github/workflows/dev.yml
index 240bbaa9..080f06e5 100644
--- a/.github/workflows/dev.yml
+++ b/.github/workflows/dev.yml
@@ -195,6 +195,17 @@ jobs:
       - name: Test with coverage
         run: yarn workspace codingbuddy-claude-plugin test:coverage
 
+  plugin-validate-commands:
+    needs: install-dependencies
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: ./.github/actions/setup
+
+      - name: Validate commands (collision guardrails)
+        run: yarn workspace codingbuddy-claude-plugin validate:commands
+
   plugin-build:
     needs: install-dependencies
     runs-on: ubuntu-latest
diff --git a/packages/claude-code-plugin/package.json b/packages/claude-code-plugin/package.json
index ed5cbfd2..7104594c 100644
--- a/packages/claude-code-plugin/package.json
+++ b/packages/claude-code-plugin/package.json
@@ -44,6 +44,7 @@
     "typecheck": "tsc --noEmit",
     "circular": "madge --circular --extensions ts src/",
     "format:check": "prettier --check \"src/**/*.ts\" \"scripts/**/*.ts\"",
+    "validate:commands": "npx tsx scripts/validate-commands.ts",
     "test": "vitest run",
     "test:hooks": "python3 -m pytest tests/ -v --tb=short",
     "test:all": "vitest run && python3 -m pytest tests/ -v --tb=short",
diff --git a/packages/claude-code-plugin/scripts/validate-commands.spec.ts b/packages/claude-code-plugin/scripts/validate-commands.spec.ts
new file mode 100644
index 00000000..abaeda0b
--- /dev/null
+++ b/packages/claude-code-plugin/scripts/validate-commands.spec.ts
@@ -0,0 +1,275 @@
+/**
+ * Tests for validate-commands script
+ *
+ * Verifies collision guardrails for reserved slash commands:
+ * 1. Reserved denylist includes known Claude Code commands
+ * 2. Command extraction from commands/ directory
+ * 3. Legacy allowlist prevents false positives
+ * 4. Forbidden bare commands trigger failure
+ * 5. Namespaced commands pass validation
+ * 6. Collision detection works correctly
+ */
+
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import * as fs from 'fs';
+import * as path from 'path';
+
+import {
+  RESERVED_COMMANDS,
+  LEGACY_ALLOWLIST,
+  extractCommandsFromDirectory,
+  getBaseCommandName,
+  isNamespaced,
+  isReservedCommand,
+  validateCommands,
+} from './validate-commands';
+
+// ============================================================================
+// Reserved Denylist
+// ============================================================================
+
+describe('reserved command denylist', () => {
+  it('includes known Claude Code built-in commands', () => {
+    const knownBuiltins = [
+      'help',
+      'clear',
+      'exit',
+      'memory',
+      'status',
+      'doctor',
+      'model',
+      'vim',
+      'review',
+      'config',
+      'init',
+      'mcp',
+      'login',
+      'logout',
+      'cost',
+      'compact',
+      'permissions',
+      'listen',
+      'bug',
+      'terminal-setup',
+    ];
+
+    for (const cmd of knownBuiltins) {
+      expect(RESERVED_COMMANDS.has(cmd)).toBe(true);
+    }
+  });
+
+  it('is a non-empty set', () => {
+    expect(RESERVED_COMMANDS.size).toBeGreaterThan(20);
+  });
+
+  it('does not include plugin-specific commands', () => {
+    expect(RESERVED_COMMANDS.has('plan')).toBe(false);
+    expect(RESERVED_COMMANDS.has('act')).toBe(false);
+    expect(RESERVED_COMMANDS.has('eval')).toBe(false);
+    expect(RESERVED_COMMANDS.has('buddy')).toBe(false);
+  });
+});
+
+// ============================================================================
+// Legacy Allowlist
+// ============================================================================
+
+describe('legacy allowlist', () => {
+  it('contains current bare commands', () => {
+    const expected = ['plan', 'act', 'eval', 'auto', 'buddy', 'checklist'];
+    for (const cmd of expected) {
+      expect(LEGACY_ALLOWLIST.has(cmd)).toBe(true);
+    }
+  });
+
+  it('does not overlap with reserved commands', () => {
+    for (const cmd of LEGACY_ALLOWLIST) {
+      expect(RESERVED_COMMANDS.has(cmd)).toBe(false);
+    }
+  });
+});
+
+// ============================================================================
+// Command Extraction
+// ============================================================================
+
+describe('extractCommandsFromDirectory', () => {
+  const tmpDir = path.join(__dirname, '..', '__test_commands_tmp__');
+
+  beforeEach(() => {
+    fs.mkdirSync(tmpDir, { recursive: true });
+  });
+
+  afterEach(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  it('extracts command names from .md files', () => {
+    fs.writeFileSync(path.join(tmpDir, 'plan.md'), '# Plan');
+    fs.writeFileSync(path.join(tmpDir, 'act.md'), '# Act');
+
+    const commands = extractCommandsFromDirectory(tmpDir);
+    expect(commands).toContain('plan');
+    expect(commands).toContain('act');
+    expect(commands).toHaveLength(2);
+  });
+
+  it('ignores non-.md files', () => {
+    fs.writeFileSync(path.join(tmpDir, 'plan.md'), '# Plan');
+    fs.writeFileSync(path.join(tmpDir, 'notes.txt'), 'notes');
+    fs.writeFileSync(path.join(tmpDir, 'config.json'), '{}');
+
+    const commands = extractCommandsFromDirectory(tmpDir);
+    expect(commands).toEqual(['plan']);
+  });
+
+  it('returns empty array for non-existent directory', () => {
+    const commands = extractCommandsFromDirectory('/nonexistent/path');
+    expect(commands).toEqual([]);
+  });
+
+  it('returns empty array for empty directory', () => {
+    const commands = extractCommandsFromDirectory(tmpDir);
+    expect(commands).toEqual([]);
+  });
+
+  it('detects the real commands/ directory', () => {
+    const realCommandsDir = path.resolve(__dirname, '..', 'commands');
+    const commands = extractCommandsFromDirectory(realCommandsDir);
+
+    expect(commands).toContain('plan');
+    expect(commands).toContain('act');
+    expect(commands).toContain('eval');
+    expect(commands).toContain('auto');
+    expect(commands).toContain('buddy');
+    expect(commands).toContain('checklist');
+    expect(commands.length).toBeGreaterThanOrEqual(6);
+  });
+});
+
+// ============================================================================
+// Namespace Helpers
+// ============================================================================
+
+describe('getBaseCommandName', () => {
+  it('strips namespace prefix', () => {
+    expect(getBaseCommandName('codingbuddy:plan')).toBe('plan');
+  });
+
+  it('returns bare name as-is', () => {
+    expect(getBaseCommandName('plan')).toBe('plan');
+  });
+
+  it('handles nested colons', () => {
+    expect(getBaseCommandName('codingbuddy:sub:cmd')).toBe('sub:cmd');
+  });
+});
+
+describe('isNamespaced', () => {
+  it('returns true for namespaced commands', () => {
+    expect(isNamespaced('codingbuddy:plan')).toBe(true);
+  });
+
+  it('returns false for bare commands', () => {
+    expect(isNamespaced('plan')).toBe(false);
+  });
+
+  it('returns false for other namespaces', () => {
+    expect(isNamespaced('other:plan')).toBe(false);
+  });
+});
+
+// ============================================================================
+// Collision Detection
+// ============================================================================
+
+describe('isReservedCommand', () => {
+  it('detects reserved bare commands', () => {
+    expect(isReservedCommand('help')).toBe(true);
+    expect(isReservedCommand('mcp')).toBe(true);
+    expect(isReservedCommand('config')).toBe(true);
+  });
+
+  it('detects reserved commands even with namespace', () => {
+    expect(isReservedCommand('codingbuddy:help')).toBe(true);
+    expect(isReservedCommand('codingbuddy:mcp')).toBe(true);
+  });
+
+  it('returns false for non-reserved commands', () => {
+    expect(isReservedCommand('plan')).toBe(false);
+    expect(isReservedCommand('buddy')).toBe(false);
+    expect(isReservedCommand('codingbuddy:plan')).toBe(false);
+  });
+});
+
+// ============================================================================
+// Full Validation
+// ============================================================================
+
+describe('validateCommands', () => {
+  const tmpDir = path.join(__dirname, '..', '__test_validate_tmp__');
+
+  beforeEach(() => {
+    fs.mkdirSync(tmpDir, { recursive: true });
+  });
+
+  afterEach(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  it('passes with current legacy commands', () => {
+    for (const cmd of LEGACY_ALLOWLIST) {
+      fs.writeFileSync(path.join(tmpDir, `${cmd}.md`), `# ${cmd}`);
+    }
+
+    const result = validateCommands(tmpDir);
+    expect(result.valid).toBe(true);
+    expect(result.collisions).toHaveLength(0);
+    expect(result.namespaceViolations).toHaveLength(0);
+  });
+
+  it('fails when a reserved command is introduced', () => {
+    fs.writeFileSync(path.join(tmpDir, 'help.md'), '# Help');
+
+    const result = validateCommands(tmpDir);
+    expect(result.valid).toBe(false);
+    expect(result.collisions).toContain('help');
+  });
+
+  it('fails when a bare command is not in legacy allowlist', () => {
+    fs.writeFileSync(path.join(tmpDir, 'my-new-command.md'), '# New');
+
+    const result = validateCommands(tmpDir);
+    expect(result.valid).toBe(false);
+    expect(result.namespaceViolations).toContain('my-new-command');
+  });
+
+  it('reports both collision and namespace violation for reserved bare command', () => {
+    fs.writeFileSync(path.join(tmpDir, 'mcp.md'), '# MCP');
+
+    const result = validateCommands(tmpDir);
+    expect(result.valid).toBe(false);
+    expect(result.collisions).toContain('mcp');
+    expect(result.namespaceViolations).toContain('mcp');
+  });
+
+  it('handles empty commands directory', () => {
+    const result = validateCommands(tmpDir);
+    expect(result.valid).toBe(true);
+    expect(result.commands).toHaveLength(0);
+  });
+
+  it('handles non-existent directory', () => {
+    const result = validateCommands('/nonexistent/path');
+    expect(result.valid).toBe(true);
+    expect(result.commands).toHaveLength(0);
+  });
+
+  it('validates the real commands/ directory passes', () => {
+    const realCommandsDir = path.resolve(__dirname, '..', 'commands');
+    const result = validateCommands(realCommandsDir);
+    expect(result.valid).toBe(true);
+    expect(result.collisions).toHaveLength(0);
+    expect(result.namespaceViolations).toHaveLength(0);
+  });
+});
diff --git a/packages/claude-code-plugin/scripts/validate-commands.ts b/packages/claude-code-plugin/scripts/validate-commands.ts
new file mode 100644
index 00000000..7b341689
--- /dev/null
+++ b/packages/claude-code-plugin/scripts/validate-commands.ts
@@ -0,0 +1,276 @@
+#!/usr/bin/env ts-node
+/**
+ * Validate Commands Script
+ *
+ * Collision guardrails for reserved slash commands.
+ * Detects when a plugin command name collides with Claude Code built-in commands.
+ *
+ * Checks:
+ * 1. Reserved command denylist (Claude Code built-ins)
+ * 2. Command extraction from commands/ directory
+ * 3. Collision detection against denylist
+ * 4. Namespace validation (codingbuddy:* convention)
+ *
+ * Usage:
+ *   npx tsx scripts/validate-commands.ts
+ */
+
+import * as path from 'path';
+import * as fs from 'fs';
+
+// ============================================================================
+// Reserved Command Denylist
+// ============================================================================
+
+/**
+ * Claude Code built-in / reserved slash command names.
+ * Source: checked-in snapshot for deterministic, repo-local validation.
+ *
+ * Maintain this list when new Claude Code built-in commands are discovered.
+ */
+export const RESERVED_COMMANDS: ReadonlySet<string> = new Set([
+  // Core session commands
+  'help',
+  'clear',
+  'exit',
+  'quit',
+  'compact',
+  'reset',
+
+  // Configuration & settings
+  'config',
+  'model',
+  'permissions',
+  'vim',
+  'terminal-setup',
+  'init',
+  'settings',
+
+  // Authentication
+  'login',
+  'logout',
+
+  // Diagnostics & info
+  'status',
+  'doctor',
+  'cost',
+  'bug',
+  'version',
+
+  // Memory & context
+  'memory',
+  'context',
+
+  // MCP & tools
+  'mcp',
+  'tools',
+
+  // Code review & tasks
+  'review',
+
+  // Session management
+  'listen',
+  'resume',
+  'continue',
+
+  // IDE integration
+  'ide',
+
+  // Other known built-ins
+  'add-dir',
+  'release-notes',
+  'pr-review',
+  'fast',
+]);
+
+// ============================================================================
+// Legacy Allowlist
+// ============================================================================
+
+/**
+ * Known legacy bare commands that are intentionally kept without namespace prefix.
+ * These existed before the codingbuddy:* namespace convention.
+ * New commands MUST use the codingbuddy:* namespace.
+ */
+export const LEGACY_ALLOWLIST: ReadonlySet<string> = new Set([
+  'plan',
+  'act',
+  'eval',
+  'auto',
+  'buddy',
+  'checklist',
+]);
+
+// ============================================================================
+// Plugin Namespace
+// ============================================================================
+
+export const PLUGIN_NAMESPACE = 'codingbuddy';
+export const NAMESPACE_SEPARATOR = ':';
+
+// ============================================================================
+// Validation Types
+// ============================================================================
+
+export interface ValidationResult {
+  valid: boolean;
+  commands: string[];
+  collisions: string[];
+  namespaceViolations: string[];
+  errors: string[];
+}
+
+// ============================================================================
+// Command Extraction
+// ============================================================================
+
+/**
+ * Extracts command names from the commands/ directory.
+ * Each .md file in commands/ represents a slash command.
+ * Filename (without extension) is the command name.
+ */
+export function extractCommandsFromDirectory(commandsDir: string): string[] {
+  if (!fs.existsSync(commandsDir)) {
+    return [];
+  }
+
+  return fs
+    .readdirSync(commandsDir)
+    .filter(file => file.endsWith('.md'))
+    .map(file => path.basename(file, '.md'));
+}
+
+/**
+ * Extracts the base command name, stripping any namespace prefix.
+ * e.g., "codingbuddy:plan" → "plan", "plan" → "plan"
+ */
+export function getBaseCommandName(command: string): string {
+  const separatorIndex = command.indexOf(NAMESPACE_SEPARATOR);
+  if (separatorIndex === -1) {
+    return command;
+  }
+  return command.substring(separatorIndex + 1);
+}
+
+/**
+ * Checks if a command uses the plugin namespace.
+ * e.g., "codingbuddy:plan" → true, "plan" → false
+ */
+export function isNamespaced(command: string): boolean {
+  return command.startsWith(`${PLUGIN_NAMESPACE}${NAMESPACE_SEPARATOR}`);
+}
+
+// ============================================================================
+// Collision Detection
+// ============================================================================
+
+/**
+ * Checks a single command name against the reserved denylist.
+ * Returns true if the command collides with a reserved name.
+ */
+export function isReservedCommand(command: string): boolean {
+  const baseName = getBaseCommandName(command);
+  return RESERVED_COMMANDS.has(baseName);
+}
+
+// ============================================================================
+// Main Validation
+// ============================================================================
+
+/**
+ * Validates all commands for collisions and namespace compliance.
+ *
+ * Rules:
+ * 1. No command may collide with a reserved Claude Code built-in
+ * 2. Bare (non-namespaced) commands must be in the legacy allowlist
+ * 3. New commands must use the codingbuddy:* namespace
+ */
+export function validateCommands(commandsDir: string): ValidationResult {
+  const result: ValidationResult = {
+    valid: true,
+    commands: [],
+    collisions: [],
+    namespaceViolations: [],
+    errors: [],
+  };
+
+  try {
+    const commands = extractCommandsFromDirectory(commandsDir);
+    result.commands = commands;
+
+    for (const cmd of commands) {
+      // Check collision with reserved commands
+      if (isReservedCommand(cmd)) {
+        result.collisions.push(cmd);
+        result.valid = false;
+      }
+
+      // Check namespace compliance: bare commands must be in legacy allowlist
+      if (!isNamespaced(cmd) && !LEGACY_ALLOWLIST.has(cmd)) {
+        result.namespaceViolations.push(cmd);
+        result.valid = false;
+      }
+    }
+  } catch (error) {
+    result.errors.push(error instanceof Error ? error.message : String(error));
+    result.valid = false;
+  }
+
+  return result;
+}
+
+// ============================================================================
+// CLI Runner
+// ============================================================================
+
+function main(): void {
+  const pluginRoot = path.resolve(__dirname, '..');
+  const commandsDir = path.join(pluginRoot, 'commands');
+
+  console.log('🔍 Validating plugin commands...\n');
+
+  const result = validateCommands(commandsDir);
+
+  console.log(`Commands found: ${result.commands.join(', ') || '(none)'}`);
+  console.log(`Reserved denylist size: ${RESERVED_COMMANDS.size}`);
+  console.log(`Legacy allowlist: ${[...LEGACY_ALLOWLIST].join(', ')}`);
+  console.log('');
+
+  if (result.collisions.length > 0) {
+    console.error('❌ COLLISION DETECTED:');
+    for (const cmd of result.collisions) {
+      console.error(`   "${cmd}" collides with a reserved Claude Code command`);
+    }
+    console.error('');
+  }
+
+  if (result.namespaceViolations.length > 0) {
+    console.error('❌ NAMESPACE VIOLATION:');
+    for (const cmd of result.namespaceViolations) {
+      console.error(
+        `   "${cmd}" is a bare command not in the legacy allowlist. Use "${PLUGIN_NAMESPACE}:${cmd}" instead.`,
+      );
+    }
+    console.error('');
+  }
+
+  if (result.errors.length > 0) {
+    console.error('❌ ERRORS:');
+    for (const err of result.errors) {
+      console.error(`   ${err}`);
+    }
+    console.error('');
+  }
+
+  if (result.valid) {
+    console.log('✅ All commands passed validation.');
+  } else {
+    console.error('❌ Command validation failed.');
+    process.exit(1);
+  }
+}
+
+// Only run CLI when executed directly (not imported)
+if (require.main === module) {
+  main();
+}