docs: add hierarchical AGENTS.md for hooks, tools, features

Create directory-specific knowledge bases for high-complexity directories:
- src/hooks/AGENTS.md: Documents 21 hooks across 86 files
- src/tools/AGENTS.md: Documents 11 LSP tools, AST-Grep, MCP, background tasks (50 files)
- src/features/AGENTS.md: Documents 6 Claude Code compatibility features (24 files)

Root AGENTS.md updated to reference these specialized guides while maintaining project overview. Enables better navigation and reduces cognitive load for developers working in specific areas.

🤖 Generated with assistance of OhMyOpenCode (https://github.com/code-yeongyu/oh-my-opencode)

src/hooks/AGENTS.md

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+# HOOKS KNOWLEDGE BASE
+
+## OVERVIEW
+
+Lifecycle hooks that intercept/modify agent behavior. Inject context, enforce rules, recover from errors, notify on events.
+
+## STRUCTURE
+
+```
+hooks/
+├── agent-usage-reminder/       # Remind to use specialized agents
+├── anthropic-auto-compact/     # Auto-compact Claude at token limit
+├── auto-update-checker/        # Version update notifications
+├── background-notification/    # OS notify on background task complete
+├── claude-code-hooks/          # Claude Code settings.json integration
+├── comment-checker/            # Prevent excessive AI comments
+│   ├── filters/                # Filtering rules (docstring, directive, bdd, etc.)
+│   └── output/                 # Output formatting
+├── compaction-context-injector/ # Inject context during compaction
+├── directory-agents-injector/  # Auto-inject AGENTS.md files
+├── directory-readme-injector/  # Auto-inject README.md files
+├── empty-message-sanitizer/    # Sanitize empty messages
+├── interactive-bash-session/   # Tmux session management
+├── keyword-detector/           # Detect ultrawork/search keywords
+├── non-interactive-env/        # CI/headless environment handling
+├── preemptive-compaction/      # Pre-emptive session compaction
+├── rules-injector/             # Conditional rules from .claude/rules/
+├── session-recovery/           # Recover from session errors
+├── think-mode/                 # Auto-detect thinking triggers
+├── context-window-monitor.ts   # Monitor context usage (standalone)
+├── empty-task-response-detector.ts
+├── session-notification.ts     # OS notify on idle (standalone)
+├── todo-continuation-enforcer.ts # Force TODO completion (standalone)
+└── tool-output-truncator.ts    # Truncate verbose outputs (standalone)
+```
+
+## HOOK CATEGORIES
+
+| Category | Hooks | Purpose |
+|----------|-------|---------|
+| Context Injection | directory-agents-injector, directory-readme-injector, rules-injector, compaction-context-injector | Auto-inject relevant context |
+| Session Management | session-recovery, anthropic-auto-compact, preemptive-compaction, empty-message-sanitizer | Handle session lifecycle |
+| Output Control | comment-checker, tool-output-truncator | Control agent output quality |
+| Notifications | session-notification, background-notification, auto-update-checker | OS/user notifications |
+| Behavior Enforcement | todo-continuation-enforcer, keyword-detector, think-mode, agent-usage-reminder | Enforce agent behavior |
+| Environment | non-interactive-env, interactive-bash-session, context-window-monitor | Adapt to runtime environment |
+| Compatibility | claude-code-hooks | Claude Code settings.json support |
+
+## HOW TO ADD A HOOK
+
+1. Create directory: `src/hooks/my-hook/`
+2. Create files:
+   - `index.ts`: Export `createMyHook(input: PluginInput)`
+   - `constants.ts`: Hook name constant
+   - `types.ts`: TypeScript interfaces (optional)
+   - `storage.ts`: Persistent state (optional)
+3. Return event handlers: `{ PreToolUse?, PostToolUse?, UserPromptSubmit?, Stop?, onSummarize? }`
+4. Export from `src/hooks/index.ts`
+5. Register in main plugin
+
+## HOOK EVENTS
+
+| Event | Timing | Can Block | Use Case |
+|-------|--------|-----------|----------|
+| PreToolUse | Before tool exec | Yes | Validate, modify input |
+| PostToolUse | After tool exec | No | Add context, warnings |
+| UserPromptSubmit | On user prompt | Yes | Inject messages, block |
+| Stop | Session idle | No | Inject follow-ups |
+| onSummarize | During compaction | No | Preserve critical context |
+
+## COMMON PATTERNS
+
+- **Storage**: Use `storage.ts` with JSON file for persistent state across sessions
+- **Once-per-session**: Track injected paths in Set to avoid duplicate injection
+- **Message injection**: Return `{ messages: [...] }` from event handlers
+- **Blocking**: Return `{ blocked: true, message: "reason" }` from PreToolUse
+
+## ANTI-PATTERNS (HOOKS)
+
+- **Heavy computation** in PreToolUse: Slows every tool call
+- **Blocking without clear reason**: Always provide actionable message
+- **Duplicate injection**: Track what's already injected per session
+- **Ignoring errors**: Always try/catch, log failures, don't crash session