Add before/after session events with cancellation support

- Merge branch event into session with before_branch/branch reasons
- Add before_switch, before_clear, shutdown reasons
- before_* events can be cancelled with { cancel: true }
- Update RPC commands to return cancelled status
- Add shutdown event on process exit
- New example hooks: confirm-destructive, dirty-repo-guard, auto-commit-on-exit

fixes #278

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -1162,8 +1162,7 @@ export class InteractiveMode {
 	private handleCtrlC(): void {
 		const now = Date.now();
 		if (now - this.lastSigintTime < 500) {
-			this.stop();
-			process.exit(0);
+			void this.shutdown();
 		} else {
 			this.clearEditor();
 			this.lastSigintTime = now;
@@ -1172,6 +1171,27 @@ export class InteractiveMode {
 
 	private handleCtrlD(): void {
 		// Only called when editor is empty (enforced by CustomEditor)
+		void this.shutdown();
+	}
+
+	/**
+	 * Gracefully shutdown the agent.
+	 * Emits shutdown event to hooks, then exits.
+	 */
+	private async shutdown(): Promise<void> {
+		// Emit shutdown event to hooks
+		const hookRunner = this.session.hookRunner;
+		if (hookRunner?.hasHandlers("session")) {
+			const entries = this.sessionManager.loadEntries();
+			await hookRunner.emit({
+				type: "session",
+				entries,
+				sessionFile: this.session.sessionFile,
+				previousSessionFile: null,
+				reason: "shutdown",
+			});
+		}
+
 		this.stop();
 		process.exit(0);
 	}
@@ -1496,8 +1516,8 @@ export class InteractiveMode {
 				userMessages.map((m) => ({ index: m.entryIndex, text: m.text })),
 				async (entryIndex) => {
 					const result = await this.session.branch(entryIndex);
-					if (result.skipped) {
-						// Hook requested to skip conversation restore
+					if (result.cancelled) {
+						// Hook cancelled the branch
 						done();
 						this.ui.requestRender();
 						return;
@@ -1533,8 +1553,7 @@ export class InteractiveMode {
 					this.ui.requestRender();
 				},
 				() => {
-					this.stop();
-					process.exit(0);
+					void this.shutdown();
 				},
 			);
 			return { component: selector, focus: selector.getSessionList() };

packages/coding-agent/src/modes/rpc/rpc-client.ts

@@ -186,9 +186,11 @@ export class RpcClient {
 
 	/**
 	 * Reset session (clear all messages).
+	 * @returns Object with `cancelled: true` if a hook cancelled the reset
 	 */
-	async reset(): Promise<void> {
-		await this.send({ type: "reset" });
+	async reset(): Promise<{ cancelled: boolean }> {
+		const response = await this.send({ type: "reset" });
+		return this.getData(response);
 	}
 
 	/**
@@ -311,15 +313,18 @@ export class RpcClient {
 
 	/**
 	 * Switch to a different session file.
+	 * @returns Object with `cancelled: true` if a hook cancelled the switch
 	 */
-	async switchSession(sessionPath: string): Promise<void> {
-		await this.send({ type: "switch_session", sessionPath });
+	async switchSession(sessionPath: string): Promise<{ cancelled: boolean }> {
+		const response = await this.send({ type: "switch_session", sessionPath });
+		return this.getData(response);
 	}
 
 	/**
 	 * Branch from a specific message.
+	 * @returns Object with `text` (the message text) and `cancelled` (if hook cancelled)
 	 */
-	async branch(entryIndex: number): Promise<{ text: string }> {
+	async branch(entryIndex: number): Promise<{ text: string; cancelled: boolean }> {
 		const response = await this.send({ type: "branch", entryIndex });
 		return this.getData(response);
 	}

packages/coding-agent/src/modes/rpc/rpc-mode.ts

@@ -205,8 +205,8 @@ export async function runRpcMode(session: AgentSession): Promise<never> {
 			}
 
 			case "reset": {
-				await session.reset();
-				return success(id, "reset");
+				const cancelled = !(await session.reset());
+				return success(id, "reset", { cancelled });
 			}
 
 			// =================================================================
@@ -339,13 +339,13 @@ export async function runRpcMode(session: AgentSession): Promise<never> {
 			}
 
 			case "switch_session": {
-				await session.switchSession(command.sessionPath);
-				return success(id, "switch_session");
+				const cancelled = !(await session.switchSession(command.sessionPath));
+				return success(id, "switch_session", { cancelled });
 			}
 
 			case "branch": {
 				const result = await session.branch(command.entryIndex);
-				return success(id, "branch", { text: result.selectedText, skipped: result.skipped });
+				return success(id, "branch", { text: result.selectedText, cancelled: result.cancelled });
 			}
 
 			case "get_branch_messages": {

packages/coding-agent/src/modes/rpc/rpc-types.ts

@@ -86,7 +86,7 @@ export type RpcResponse =
 	| { id?: string; type: "response"; command: "prompt"; success: true }
 	| { id?: string; type: "response"; command: "queue_message"; success: true }
 	| { id?: string; type: "response"; command: "abort"; success: true }
-	| { id?: string; type: "response"; command: "reset"; success: true }
+	| { id?: string; type: "response"; command: "reset"; success: true; data: { cancelled: boolean } }
 
 	// State
 	| { id?: string; type: "response"; command: "get_state"; success: true; data: RpcSessionState }
@@ -142,8 +142,8 @@ export type RpcResponse =
 	// Session
 	| { id?: string; type: "response"; command: "get_session_stats"; success: true; data: SessionStats }
 	| { id?: string; type: "response"; command: "export_html"; success: true; data: { path: string } }
-	| { id?: string; type: "response"; command: "switch_session"; success: true }
-	| { id?: string; type: "response"; command: "branch"; success: true; data: { text: string } }
+	| { id?: string; type: "response"; command: "switch_session"; success: true; data: { cancelled: boolean } }
+	| { id?: string; type: "response"; command: "branch"; success: true; data: { text: string; cancelled: boolean } }
 	| {
 			id?: string;
 			type: "response";