Custom tools with session lifecycle, examples for hooks and tools

- Custom tools: TypeScript modules that extend pi with new tools
  - Custom TUI rendering via renderCall/renderResult
  - User interaction via pi.ui (select, confirm, input, notify)
  - Session lifecycle via onSession callback for state reconstruction
  - Examples: todo.ts, question.ts, hello.ts

- Hook examples: permission-gate, git-checkpoint, protected-paths

- Session lifecycle centralized in AgentSession
  - Works across all modes (interactive, print, RPC)
  - Unified session event for hooks (replaces session_start/session_switch)

- Box component added to pi-tui

- Examples bundled in npm and binary releases

Fixes #190

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,16 @@
 
 ## [Unreleased]
 
+### Added
+
+- **Custom tools**: Extend pi with custom tools written in TypeScript. Tools can provide custom TUI rendering, interact with users via `pi.ui` (select, confirm, input, notify), and maintain state across sessions via `onSession` callback. See [docs/custom-tools.md](docs/custom-tools.md) and [examples/custom-tools/](examples/custom-tools/). ([#190](https://github.com/badlogic/pi-mono/issues/190))
+
+- **Hook and tool examples**: Added `examples/hooks/` and `examples/custom-tools/` with working examples. Examples are now bundled in npm and binary releases.
+
+### Breaking Changes
+
+- **Hooks**: Replaced `session_start` and `session_switch` events with unified `session` event. Use `event.reason` (`"start" | "switch" | "clear"`) to distinguish. Event now includes `entries` array for state reconstruction.
+
 ## [0.22.5] - 2025-12-17
 
 ### Fixed