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/src/core/index.ts

@@ -13,6 +13,18 @@ export {
 	type SessionStats,
 } from "./agent-session.js";
 export { type BashExecutorOptions, type BashResult, executeBash } from "./bash-executor.js";
+export {
+	type CustomAgentTool,
+	type CustomToolFactory,
+	type CustomToolsLoadResult,
+	discoverAndLoadCustomTools,
+	type ExecResult,
+	type LoadedCustomTool,
+	loadCustomTools,
+	type RenderResultOptions,
+	type ToolAPI,
+	type ToolUIContext,
+} from "./custom-tools/index.js";
 export {
 	type HookAPI,
 	type HookError,