docs: Add multi-agent support documentation

Update documentation for PR #270 multi-agent enhancement feature:
- CHANGELOG.md: Add comprehensive section for multi-agent support
- README.md: Update LOCAL Enhancement section with agent options
- ENHANCEMENT_MODES.md: Add multi-agent guide with security details

Includes:
- Agent selection (claude, codex, copilot, opencode, custom)
- CLI flags and environment variables
- Security validation details
- Agent aliases and normalization
- Usage examples for all modes

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -9,6 +9,31 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+#### Multi-Agent Support for Local Enhancement (NEW)
+- **Multiple Coding Agent Support**: Choose your preferred local coding agent for SKILL.md enhancement
+  - **Claude Code** (default): Claude Code CLI with `--dangerously-skip-permissions`
+  - **Codex CLI**: OpenAI Codex CLI with `--full-auto` and `--skip-git-repo-check`
+  - **Copilot CLI**: GitHub Copilot CLI (`gh copilot chat`)
+  - **OpenCode CLI**: OpenCode CLI
+  - **Custom agents**: Use any CLI tool with `--agent custom --agent-cmd "command {prompt_file}"`
+- **CLI Arguments**: New flags for agent selection
+  - `--agent`: Choose agent (claude, codex, copilot, opencode, custom)
+  - `--agent-cmd`: Override command template for custom agents
+- **Environment Variables**: CI/CD friendly configuration
+  - `SKILL_SEEKER_AGENT`: Default agent to use
+  - `SKILL_SEEKER_AGENT_CMD`: Default command template for custom agents
+- **Security First**: Custom command validation
+  - Blocks dangerous shell characters (`;`, `&`, `|`, `$`, `` ` ``, `\n`, `\r`)
+  - Validates executable exists in PATH
+  - Safe parsing with `shlex.split()`
+- **Dual Input Modes**: Supports both file-based and stdin-based agents
+  - File-based: Uses `{prompt_file}` placeholder (Claude, custom agents)
+  - Stdin-based: Pipes prompt via stdin (Codex CLI)
+- **Backward Compatible**: Claude Code remains the default, no breaking changes
+- **Comprehensive Tests**: 13 new tests covering all agent types and security validation
+- **Agent Normalization**: Smart alias handling (e.g., "claude-code" → "claude")
+- **Credit**: Contributed by @rovo79 (Robert Dean) via PR #270
+
 #### C3.10: Signal Flow Analysis for Godot Projects (NEW)
 - **Complete Signal Flow Analysis System**: Analyze event-driven architectures in Godot game projects
   - Signal declaration extraction (`signal` keyword detection)

README.md

@@ -1560,8 +1560,24 @@ skill-seekers enhance output/react/
 - **Quality:** Transforms 75-line templates into 500+ line comprehensive guides
 
 **LOCAL Enhancement (Recommended):**
-- Uses your Claude Code Max plan (no API costs)
-- Opens new terminal with Claude Code
+- Uses your local coding agent (no API costs)
+- **Multiple Agent Support:**
+  - Claude Code (default) - Your Claude Code Max plan
+  - Codex CLI - OpenAI Codex CLI
+  - Copilot CLI - GitHub Copilot CLI
+  - OpenCode CLI - OpenCode CLI
+  - Custom agents - Use any CLI tool
+- Choose agent with `--agent` flag:
+  ```bash
+  skill-seekers enhance output/react/ --agent codex
+  skill-seekers enhance output/react/ --agent copilot
+  skill-seekers enhance output/react/ --agent custom --agent-cmd "my-agent {prompt_file}"
+  ```
+- Environment variables for CI/CD:
+  ```bash
+  export SKILL_SEEKER_AGENT=codex
+  export SKILL_SEEKER_AGENT_CMD="my-agent {prompt_file}"
+  ```
 - Analyzes reference files automatically
 - Takes 30-60 seconds
 - Quality: 9/10 (comparable to API version)

docs/features/ENHANCEMENT_MODES.md

@@ -11,6 +11,98 @@ Skill Seekers supports **4 enhancement modes** for different use cases:
 3. **Daemon** - Fully detached process, continues after parent exits
 4. **Terminal** - Opens new terminal window (interactive)
 
+## Multi-Agent Support (NEW)
+
+All enhancement modes now support **multiple local coding agents**:
+
+### Supported Agents
+
+| Agent | Display Name | Default | Notes |
+|-------|--------------|---------|-------|
+| **claude** | Claude Code | ✅ Yes | Your Claude Code Max plan (no API costs) |
+| **codex** | OpenAI Codex CLI | No | Uses `codex exec --full-auto` |
+| **copilot** | GitHub Copilot CLI | No | Uses `gh copilot chat` |
+| **opencode** | OpenCode CLI | No | Uses `opencode` command |
+| **custom** | Custom CLI Agent | No | Use any CLI tool with `--agent-cmd` |
+
+### Agent Selection
+
+**CLI Flags:**
+```bash
+# Use Codex CLI
+skill-seekers enhance output/react/ --agent codex
+
+# Use Copilot CLI
+skill-seekers enhance output/react/ --agent copilot
+
+# Use OpenCode CLI
+skill-seekers enhance output/react/ --agent opencode
+
+# Custom agent with file input
+skill-seekers enhance output/react/ --agent custom --agent-cmd "my-agent --prompt {prompt_file}"
+
+# Custom agent with stdin input
+skill-seekers enhance output/react/ --agent custom --agent-cmd "my-agent --enhance"
+```
+
+**Environment Variables (CI/CD):**
+```bash
+# Set default agent
+export SKILL_SEEKER_AGENT=codex
+skill-seekers enhance output/react/
+
+# Set custom command template
+export SKILL_SEEKER_AGENT=custom
+export SKILL_SEEKER_AGENT_CMD="my-agent {prompt_file}"
+skill-seekers enhance output/react/
+```
+
+### Agent Command Templates
+
+**File-based agents** (use `{prompt_file}` placeholder):
+```bash
+--agent-cmd "my-agent --input {prompt_file}"
+--agent-cmd "my-agent < {prompt_file}"
+```
+
+**Stdin-based agents** (no placeholder):
+```bash
+--agent-cmd "my-agent --enhance"
+```
+
+### Security
+
+Custom commands are validated for security:
+- ✅ Blocks dangerous shell characters: `;`, `&`, `|`, `$`, `` ` ``, `\n`, `\r`
+- ✅ Validates executable exists in PATH
+- ✅ Safe parsing with `shlex.split()`
+
+**Example rejection:**
+```bash
+# This will fail with security error:
+skill-seekers enhance . --agent custom --agent-cmd "evil; rm -rf /"
+# Error: Custom command contains dangerous shell characters
+```
+
+### Agent Aliases
+
+Agent names are normalized with smart alias support:
+```bash
+# All resolve to "claude"
+--agent claude
+--agent claude-code
+--agent claude_code
+--agent CLAUDE
+
+# All resolve to "codex"
+--agent codex
+--agent codex-cli
+
+# All resolve to "copilot"
+--agent copilot
+--agent copilot-cli
+```
+
 ## Mode Comparison
 
 | Feature | Headless | Background | Daemon | Terminal |
@@ -28,18 +120,25 @@ Skill Seekers supports **4 enhancement modes** for different use cases:
 **When to use**: CI/CD pipelines, automation scripts, when you want to wait for completion
 
 ```bash
-# Basic usage - waits until done
+# Basic usage - waits until done (uses Claude Code by default)
 skill-seekers enhance output/react/
 
+# Use different agent
+skill-seekers enhance output/react/ --agent codex
+skill-seekers enhance output/react/ --agent copilot
+
 # With custom timeout
 skill-seekers enhance output/react/ --timeout 1200
 
 # Force mode - no confirmations
 skill-seekers enhance output/react/ --force
+
+# Combine agent + force mode
+skill-seekers enhance output/react/ --agent codex --force
 ```
 
 **Behavior**:
-- Runs `claude` CLI directly
+- Runs selected coding agent CLI directly (default: Claude Code)
 - **BLOCKS** until enhancement completes
 - Shows progress output
 - Returns exit code: 0 = success, 1 = failure
@@ -49,9 +148,13 @@ skill-seekers enhance output/react/ --force
 **When to use**: When you want to continue working while enhancement runs
 
 ```bash
-# Start enhancement in background
+# Start enhancement in background (default agent: Claude Code)
 skill-seekers enhance output/react/ --background
 
+# Start with different agent
+skill-seekers enhance output/react/ --background --agent codex
+skill-seekers enhance output/react/ --background --agent copilot
+
 # Returns immediately with status file created
 # ✅ Background enhancement started!
 # 📊 Status file: output/react/.enhancement_status.json