WP3: Add AgentSession event subscription with session persistence

packages/coding-agent/docs/refactor.md

@@ -340,9 +340,10 @@ private unsubscribeAll(): void {
 **Verification:**
 1. `npm run check` passes
 
-- [ ] Add `subscribe()` method to AgentSession
-- [ ] Add `unsubscribeAll()` private method
-- [ ] Verify with `npm run check`
+- [x] Add `subscribe()` method to AgentSession
+- [x] Add `unsubscribeAll()` method
+- [x] Add `resubscribe()` method
+- [x] Verify with `npm run check`
 
 ---
 

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

@@ -13,12 +13,15 @@
  * Modes use this class and add their own I/O layer on top.
  */
 
-import type { Agent, AgentState, AppMessage, ThinkingLevel } from "@mariozechner/pi-agent-core";
+import type { Agent, AgentEvent, AgentState, AppMessage, ThinkingLevel } from "@mariozechner/pi-agent-core";
 import type { Model } from "@mariozechner/pi-ai";
 import type { SessionManager } from "../session-manager.js";
 import type { SettingsManager } from "../settings-manager.js";
 import type { FileSlashCommand } from "../slash-commands.js";
 
+/** Listener function for agent events */
+export type AgentEventListener = (event: AgentEvent) => void;
+
 // ============================================================================
 // Types
 // ============================================================================
@@ -45,6 +48,10 @@ export class AgentSession {
 	private _scopedModels: Array<{ model: Model<any>; thinkingLevel: ThinkingLevel }>;
 	private _fileCommands: FileSlashCommand[];
 
+	// Event subscription state
+	private _unsubscribeAgent?: () => void;
+	private _eventListeners: AgentEventListener[] = [];
+
 	constructor(config: AgentSessionConfig) {
 		this.agent = config.agent;
 		this.sessionManager = config.sessionManager;
@@ -53,6 +60,87 @@ export class AgentSession {
 		this._fileCommands = config.fileCommands ?? [];
 	}
 
+	// =========================================================================
+	// Event Subscription
+	// =========================================================================
+
+	/**
+	 * Subscribe to agent events.
+	 * Session persistence is handled internally (saves messages on message_end).
+	 * Multiple listeners can be added. Returns unsubscribe function for this listener.
+	 */
+	subscribe(listener: AgentEventListener): () => void {
+		this._eventListeners.push(listener);
+
+		// Set up agent subscription if not already done
+		if (!this._unsubscribeAgent) {
+			this._unsubscribeAgent = this.agent.subscribe(async (event) => {
+				// Notify all listeners
+				for (const l of this._eventListeners) {
+					l(event);
+				}
+
+				// Handle session persistence
+				if (event.type === "message_end") {
+					this.sessionManager.saveMessage(event.message);
+
+					// Initialize session after first user+assistant exchange
+					if (this.sessionManager.shouldInitializeSession(this.agent.state.messages)) {
+						this.sessionManager.startSession(this.agent.state);
+					}
+
+					// Check auto-compaction after assistant messages
+					// (will be implemented in WP7)
+					// if (event.message.role === "assistant") {
+					//   await this.checkAutoCompaction();
+					// }
+				}
+			});
+		}
+
+		// Return unsubscribe function for this specific listener
+		return () => {
+			const index = this._eventListeners.indexOf(listener);
+			if (index !== -1) {
+				this._eventListeners.splice(index, 1);
+			}
+		};
+	}
+
+	/**
+	 * Unsubscribe from agent entirely and clear all listeners.
+	 * Used during reset/cleanup operations.
+	 */
+	unsubscribeAll(): void {
+		if (this._unsubscribeAgent) {
+			this._unsubscribeAgent();
+			this._unsubscribeAgent = undefined;
+		}
+		this._eventListeners = [];
+	}
+
+	/**
+	 * Re-subscribe to agent after unsubscribeAll.
+	 * Call this after operations that require temporary unsubscription.
+	 */
+	resubscribe(): void {
+		if (this._unsubscribeAgent) return; // Already subscribed
+
+		this._unsubscribeAgent = this.agent.subscribe(async (event) => {
+			for (const l of this._eventListeners) {
+				l(event);
+			}
+
+			if (event.type === "message_end") {
+				this.sessionManager.saveMessage(event.message);
+
+				if (this.sessionManager.shouldInitializeSession(this.agent.state.messages)) {
+					this.sessionManager.startSession(this.agent.state);
+				}
+			}
+		});
+	}
+
 	// =========================================================================
 	// Read-only State Access
 	// =========================================================================