Add Agent.prompt(AppMessage) overload for custom message types

Instead of using continue() which validates roles, prompt() now accepts
an AppMessage directly. This allows hook messages with role: 'hookMessage'
to trigger proper agent loop with message events.

- Add overloads: prompt(AppMessage) and prompt(string, attachments?)
- sendHookMessage uses prompt(appMessage) instead of appendMessage+continue

packages/agent/src/agent.ts

@@ -170,13 +170,20 @@ export class Agent {
 		this.messageQueue = [];
 	}
 
-	async prompt(input: string, attachments?: Attachment[]) {
+	/** Send a prompt to the agent with an AppMessage. */
+	async prompt(message: AppMessage): Promise<void>;
+	/** Send a prompt to the agent with text and optional attachments. */
+	async prompt(input: string, attachments?: Attachment[]): Promise<void>;
+	async prompt(input: string | AppMessage, attachments?: Attachment[]) {
 		const model = this._state.model;
 		if (!model) {
 			throw new Error("No model configured");
 		}
 
-		// Build user message with attachments
+		let userMessage: AppMessage;
+
+		if (typeof input === "string") {
+			// Build user message from text + attachments
 			const content: Array<TextContent | ImageContent> = [{ type: "text", text: input }];
 			if (attachments?.length) {
 				for (const a of attachments) {
@@ -191,13 +198,16 @@ export class Agent {
 					}
 				}
 			}
-
+			userMessage = {
-		const userMessage: AppMessage = {
 				role: "user",
 				content,
 				attachments: attachments?.length ? attachments : undefined,
 				timestamp: Date.now(),
 			};
+		} else {
+			// Use provided AppMessage directly
+			userMessage = input;
+		}
 
 		await this._runAgentLoop(userMessage);
 	}

packages/coding-agent/src/core/agent-session.ts

@@ -584,10 +584,8 @@ export class AgentSession {
 			// Queue for processing by agent loop
 			await this.agent.queueMessage(appMessage);
 		} else if (triggerTurn) {
-			// Append to agent state and session, then trigger a turn
+			// Send as prompt - agent loop will emit message events
-			this.agent.appendMessage(appMessage);
+			await this.agent.prompt(appMessage);
-			// Start a new turn - emit message events for the hook message so TUI can render it
-			await this.agent.continue(true);
 		} else {
 			// Just append to agent state and session, no turn
 			this.agent.appendMessage(appMessage);

packages/coding-agent/src/core/messages.ts

@@ -115,7 +115,7 @@ export function messageTransformer(messages: AppMessage[]): Message[] {
 				};
 			}
 			if (isHookAppMessage(m)) {
-				// Convert hook message to user message
+				// Convert hook message to user message for LLM
 				return {
 					role: "user",
 					content: m.content,