Cleanup: unify HookMessage naming and simplify SessionContext

- Rename HookAppMessage to HookMessage, isHookAppMessage to isHookMessage
- Remove entries array from SessionContext (use isHookMessage type guard instead)
- HookMessage.content now accepts string directly (not just array)
- Fix streamMessage type in AgentState (AppMessage, not Message)
- Rename CustomMessageComponent to HookMessageComponent
- Fix test hook to use pi.sendMessage

packages/agent/src/agent.ts

@@ -325,15 +325,15 @@ export class Agent {
 						break;
 					}
 					case "message_update": {
-						partial = ev.message as AppMessage;
+						partial = ev.message;
 						this._state.streamMessage = ev.message as Message;
 						break;
 					}
 					case "message_end": {
 						partial = null;
 						this._state.streamMessage = null;
-						this.appendMessage(ev.message as AppMessage);
-						generatedMessages.push(ev.message as AppMessage);
+						this.appendMessage(ev.message);
+						generatedMessages.push(ev.message);
 						break;
 					}
 					case "tool_execution_start": {

packages/agent/src/types.ts

@@ -73,7 +73,7 @@ export interface AgentState {
 	tools: AgentTool<any>[];
 	messages: AppMessage[]; // Can include attachments + custom message types
 	isStreaming: boolean;
-	streamMessage: Message | null;
+	streamMessage: AppMessage | null;
 	pendingToolCalls: Set<string>;
 	error?: string;
 }