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/modes/rpc/rpc-mode.ts

@@ -120,6 +120,9 @@ export async function runRpcMode(session: AgentSession): Promise<never> {
 		},
 	});
 
+	// Load entries once for session start events
+	const entries = session.sessionManager.loadEntries();
+
 	// Set up hooks with RPC-based UI context
 	const hookRunner = session.hookRunner;
 	if (hookRunner) {
@@ -139,8 +142,31 @@ export async function runRpcMode(session: AgentSession): Promise<never> {
 				});
 			}
 		});
-		// Emit session_start event
-		await hookRunner.emit({ type: "session_start" });
+		// Emit session event
+		await hookRunner.emit({
+			type: "session",
+			entries,
+			sessionFile: session.sessionFile,
+			previousSessionFile: null,
+			reason: "start",
+		});
+	}
+
+	// Emit session start event to custom tools
+	// Note: Tools get no-op UI context in RPC mode (host handles UI via protocol)
+	for (const { tool } of session.customTools) {
+		if (tool.onSession) {
+			try {
+				await tool.onSession({
+					entries,
+					sessionFile: session.sessionFile,
+					previousSessionFile: null,
+					reason: "start",
+				});
+			} catch (_err) {
+				// Silently ignore tool errors
+			}
+		}
 	}
 
 	// Output all agent events as JSON