refactor(ext): drive heartbeat and running flag from statuschange

Project agent status into chrome.storage via a statuschange listener
instead of pairing setup/teardown across lifecycle hooks. A throwing hook
can no longer leak the heartbeat or strand isAgentRunning, and rejected
concurrent execute() calls never touch the active run's state.

packages/extension/src/agent/MultiPageAgent.ts

@@ -39,15 +39,6 @@ export class MultiPageAgent extends PageAgentCore {
 		const includeInitialTab = config.includeInitialTab ?? true
 		const experimentalIncludeAllTabs = config.experimentalIncludeAllTabs ?? false
 
-		/**
-		 * When the agent is in side-panel and user closed the side-panel.
-		 * There is no chance for isAgentRunning to be set false.
-		 * (unload event doesn't work well in side panel.)
-		 * (I'm trying not to use long-lived connection because the lifecycle of a sw is hard to predict.)
-		 * This heartbeat mechanism acts as a backup.
-		 */
-		let heartBeatInterval: null | number = null
-
 		super({
 			...config,
 			pageController: pageController as any,
@@ -56,27 +47,6 @@ export class MultiPageAgent extends PageAgentCore {
 
 			onBeforeTask: async (agent) => {
 				await tabsController.init(agent.task, { includeInitialTab, experimentalIncludeAllTabs })
-
-				heartBeatInterval = window.setInterval(() => {
-					chrome.storage.local.set({
-						agentHeartbeat: Date.now(),
-					})
-				}, 1_000)
-
-				await chrome.storage.local.set({
-					isAgentRunning: true,
-				})
-			},
-
-			onAfterTask: async () => {
-				if (heartBeatInterval) {
-					window.clearInterval(heartBeatInterval)
-					heartBeatInterval = null
-				}
-
-				await chrome.storage.local.set({
-					isAgentRunning: false,
-				})
 			},
 
 			onBeforeStep: async (agent) => {
@@ -86,17 +56,35 @@ export class MultiPageAgent extends PageAgentCore {
 			},
 
 			onDispose: () => {
-				if (heartBeatInterval) {
-					window.clearInterval(heartBeatInterval)
-					heartBeatInterval = null
-				}
-
-				chrome.storage.local.set({
-					isAgentRunning: false,
-				})
-
 				tabsController.dispose()
 			},
 		})
+
+		/**
+		 * Project agent status into chrome.storage. The content script polls
+		 * `isAgentRunning` + `agentHeartbeat` (eventually consistent by design).
+		 *
+		 * When the agent is in side-panel and user closed the side-panel.
+		 * There is no chance for isAgentRunning to be set false.
+		 * (unload event doesn't work well in side panel.)
+		 * (I'm trying not to use long-lived connection because the lifecycle of a sw is hard to predict.)
+		 * This heartbeat mechanism acts as a backup.
+		 */
+		let heartBeatInterval: number | null = null
+
+		this.addEventListener('statuschange', () => {
+			const running = this.status === 'running'
+
+			if (running && !heartBeatInterval) {
+				heartBeatInterval = window.setInterval(() => {
+					void chrome.storage.local.set({ agentHeartbeat: Date.now() })
+				}, 1_000)
+			} else if (!running && heartBeatInterval) {
+				clearInterval(heartBeatInterval)
+				heartBeatInterval = null
+			}
+
+			chrome.storage.local.set({ isAgentRunning: running }).catch(console.error)
+		})
 	}
 }