fix(coding-agent): add replacement-session callbacks closes #2860

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

@@ -53,6 +53,7 @@ import {
 	type MessageEndEvent,
 	type MessageStartEvent,
 	type MessageUpdateEvent,
+	type ReplacedSessionContext,
 	type SessionBeforeCompactResult,
 	type SessionBeforeTreeResult,
 	type SessionStartEvent,
@@ -722,6 +723,9 @@ export class AgentSession {
 	 * Call this when completely done with the session.
 	 */
 	dispose(): void {
+		this._extensionRunner.invalidate(
+			"This extension instance is stale after session replacement or reload. Use the provided replacement-session context instead.",
+		);
 		this._disconnectFromAgent();
 		this._eventListeners = [];
 	}
@@ -3066,6 +3070,16 @@ export class AgentSession {
 	// Extension System
 	// =========================================================================
 
+	createReplacedSessionContext(): ReplacedSessionContext {
+		const context = Object.defineProperties(
+			{},
+			Object.getOwnPropertyDescriptors(this._extensionRunner.createCommandContext()),
+		) as ReplacedSessionContext;
+		context.sendMessage = (message, options) => this.sendCustomMessage(message, options);
+		context.sendUserMessage = (content, options) => this.sendUserMessage(content, options);
+		return context;
+	}
+
 	/**
 	 * Check if extensions have handlers for a specific event type.
 	 */