diff --git a/packages/core/package.json b/packages/core/package.json
index 22cff18..2fcc7fb 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -48,6 +48,7 @@
     "homepage": "https://alibaba.github.io/page-agent/",
     "scripts": {
         "build": "vite build",
+        "test": "vitest run",
         "dev:iife": "concurrently \"vite build --config vite.iife.config.js --watch\" \"npx serve dist/iife -p 5174\"",
         "prepublishOnly": "node ../../scripts/pre-publish.js",
         "postpublish": "node ../../scripts/post-publish.js"
diff --git a/packages/core/src/PageAgentCore.test.ts b/packages/core/src/PageAgentCore.test.ts
new file mode 100644
index 0000000..1739026
--- /dev/null
+++ b/packages/core/src/PageAgentCore.test.ts
@@ -0,0 +1,275 @@
+import type { BrowserState, PageController } from '@page-agent/page-controller'
+import { describe, expect, it, vi } from 'vitest'
+import * as z from 'zod/v4'
+
+import { PageAgentCore, tool } from './PageAgentCore'
+import type { ExecutionResult } from './types'
+
+type TestFetch = (...args: Parameters<typeof globalThis.fetch>) => Promise<Response>
+
+function agentResponse(args: unknown): Response {
+	return new Response(
+		JSON.stringify({
+			choices: [
+				{
+					finish_reason: 'tool_calls',
+					message: {
+						tool_calls: [
+							{
+								function: {
+									name: 'AgentOutput',
+									arguments: JSON.stringify(args),
+								},
+							},
+						],
+					},
+				},
+			],
+			usage: {},
+		})
+	)
+}
+
+function createPageController(): PageController {
+	const browserState: BrowserState = {
+		url: 'https://example.test/',
+		title: 'Test page',
+		header: '',
+		content: '',
+		footer: '',
+	}
+
+	return {
+		showMask: vi.fn(async () => {}),
+		hideMask: vi.fn(),
+		cleanUpHighlights: vi.fn(),
+		getLastUpdateTime: vi.fn(() => Date.now()),
+		getBrowserState: vi.fn(async () => browserState),
+		dispose: vi.fn(),
+	} as unknown as PageController
+}
+
+function createAgent(
+	customFetch: TestFetch,
+	options: Partial<ConstructorParameters<typeof PageAgentCore>[0]> = {}
+): PageAgentCore {
+	return new PageAgentCore({
+		baseURL: 'https://llm.test',
+		model: 'test-model',
+		maxRetries: 0,
+		stepDelay: 0,
+		customFetch,
+		customSystemPrompt: 'test',
+		pageController: createPageController(),
+		...options,
+	})
+}
+
+function createFetchMock() {
+	return vi.fn<TestFetch>()
+}
+
+function onceActivity(
+	agent: PageAgentCore,
+	predicate: (detail: unknown) => boolean
+): Promise<void> {
+	return new Promise((resolve) => {
+		const onActivity = (event: Event) => {
+			if (!predicate((event as CustomEvent).detail)) return
+			agent.removeEventListener('activity', onActivity)
+			resolve()
+		}
+
+		agent.addEventListener('activity', onActivity)
+	})
+}
+
+function isExecutingTool(detail: unknown, toolName: string): boolean {
+	return (
+		typeof detail === 'object' &&
+		detail !== null &&
+		'type' in detail &&
+		'tool' in detail &&
+		detail.type === 'executing' &&
+		detail.tool === toolName
+	)
+}
+
+function doneResponse(text: string, success = true): Response {
+	return agentResponse({ action: { done: { text, success } } })
+}
+
+function waitResponse(seconds = 10): Response {
+	return agentResponse({ action: { wait: { seconds } } })
+}
+
+/**
+ * Start a task that blocks on `wait`, returning once the tool is executing.
+ * The running promise is wrapped so awaiting this helper does not await the task.
+ */
+async function startBlockedTask(
+	agent: PageAgentCore,
+	task = 'first'
+): Promise<{ result: Promise<ExecutionResult> }> {
+	const waitStarted = onceActivity(agent, (detail) => isExecutingTool(detail, 'wait'))
+	const result = agent.execute(task)
+	await waitStarted
+	return { result }
+}
+
+describe.concurrent('PageAgentCore lifecycle', () => {
+	describe('normal execution', () => {
+		it('runs a task to natural completion', async () => {
+			const fetchMock = createFetchMock().mockResolvedValueOnce(doneResponse('all done'))
+			const agent = createAgent(fetchMock)
+
+			const result = await agent.execute('do something')
+
+			expect(result).toMatchObject({ success: true, data: 'all done' })
+			expect(agent.status).toBe('completed')
+			expect(fetchMock).toHaveBeenCalledTimes(1)
+		})
+
+		it('throws when a task is already running', async () => {
+			const fetchMock = createFetchMock().mockResolvedValueOnce(waitResponse())
+			const agent = createAgent(fetchMock)
+			const { result } = await startBlockedTask(agent)
+
+			await expect(agent.execute('second')).rejects.toThrow('A task is already running.')
+
+			agent.stop()
+			await result
+		})
+	})
+
+	describe('stop', () => {
+		it('aborts the running task and keeps the agent reusable', async () => {
+			const fetchMock = createFetchMock()
+				.mockResolvedValueOnce(waitResponse())
+				.mockResolvedValueOnce(doneResponse('second task'))
+			const agent = createAgent(fetchMock)
+			const { result: firstTask } = await startBlockedTask(agent)
+
+			agent.stop()
+			await expect(firstTask).resolves.toMatchObject({ success: false, data: 'Task aborted' })
+
+			const secondTask = await agent.execute('second')
+			expect(secondTask).toMatchObject({ success: true, data: 'second task' })
+		})
+
+		it('is a no-op when no task is running', () => {
+			const agent = createAgent(createFetchMock())
+
+			expect(() => {
+				agent.stop()
+				agent.stop()
+			}).not.toThrow()
+			expect(agent.status).toBe('idle')
+		})
+	})
+
+	describe('dispose', () => {
+		it('aborts the running task and blocks further execution', async () => {
+			const fetchMock = createFetchMock().mockResolvedValueOnce(waitResponse())
+			const agent = createAgent(fetchMock)
+			const { result: task } = await startBlockedTask(agent)
+
+			agent.dispose()
+			await expect(task).resolves.toMatchObject({ success: false, data: 'Task aborted' })
+
+			expect(agent.disposed).toBe(true)
+			await expect(agent.execute('again')).rejects.toThrow('has been disposed')
+		})
+
+		it('is idempotent', () => {
+			const agent = createAgent(createFetchMock())
+
+			expect(() => {
+				agent.dispose()
+				agent.dispose()
+			}).not.toThrow()
+			expect(agent.disposed).toBe(true)
+		})
+	})
+
+	describe('error handling', () => {
+		it('fails the task when the network request rejects', async () => {
+			const fetchMock = createFetchMock().mockRejectedValue(new Error('network down'))
+			const agent = createAgent(fetchMock)
+
+			const result = await agent.execute('do something')
+
+			expect(result.success).toBe(false)
+			expect(agent.status).toBe('error')
+		})
+
+		it('fails the task when a tool throws', async () => {
+			const fetchMock = createFetchMock().mockResolvedValue(agentResponse({ action: { boom: {} } }))
+			const agent = createAgent(fetchMock, {
+				customTools: {
+					boom: tool({
+						description: 'Always throws.',
+						inputSchema: z.object({}),
+						execute: async () => {
+							throw new Error('tool exploded')
+						},
+					}),
+				},
+			})
+
+			const result = await agent.execute('trigger tool error')
+
+			expect(result.success).toBe(false)
+			expect(agent.status).toBe('error')
+		})
+	})
+
+	describe('cancellation edge cases', () => {
+		it('rejects a new task while a stopped task is settling', async () => {
+			const fetchMock = createFetchMock().mockResolvedValueOnce(waitResponse())
+			const agent = createAgent(fetchMock)
+			const { result: firstTask } = await startBlockedTask(agent)
+
+			agent.stop()
+
+			await expect(agent.execute('too early')).rejects.toThrow('A task is already running.')
+			await expect(firstTask).resolves.toMatchObject({ success: false, data: 'Task aborted' })
+			expect(fetchMock).toHaveBeenCalledTimes(1)
+		})
+
+		it('discards a custom tool result that resolves after stop', async () => {
+			let resolveTool!: () => void
+			let notifyToolStarted!: () => void
+			const toolFinished = new Promise<void>((resolve) => {
+				resolveTool = resolve
+			})
+			const toolStarted = new Promise<void>((resolve) => {
+				notifyToolStarted = resolve
+			})
+			const fetchMock = createFetchMock().mockResolvedValue(
+				agentResponse({ action: { slow_tool: {} } })
+			)
+			const agent = createAgent(fetchMock, {
+				customTools: {
+					slow_tool: tool({
+						description: 'A tool that deliberately ignores cancellation.',
+						inputSchema: z.object({}),
+						execute: async () => {
+							notifyToolStarted()
+							await toolFinished
+							return 'ignored stop'
+						},
+					}),
+				},
+			})
+
+			const task = agent.execute('run slow tool')
+			await toolStarted
+
+			agent.stop()
+			resolveTool()
+
+			await expect(task).resolves.toMatchObject({ success: false, data: 'Task aborted' })
+		})
+	})
+})
diff --git a/packages/core/vitest.config.js b/packages/core/vitest.config.js
new file mode 100644
index 0000000..323e218
--- /dev/null
+++ b/packages/core/vitest.config.js
@@ -0,0 +1,9 @@
+import { defineConfig } from 'vitest/config'
+
+export default defineConfig({
+	test: {
+		name: 'core',
+		include: ['src/**/*.test.ts'],
+		silent: 'passed-only',
+	},
+})
diff --git a/packages/llms/tsconfig.json b/packages/llms/tsconfig.json
index fb30544..d45abe9 100644
--- a/packages/llms/tsconfig.json
+++ b/packages/llms/tsconfig.json
@@ -3,6 +3,6 @@
     "compilerOptions": {
         "tsBuildInfoFile": "./node_modules/.tmp/tsconfig.tsbuildinfo"
     },
-    "include": ["**/*.ts"],
+    "include": ["src/**/*.ts"],
     "exclude": ["dist", "node_modules"]
 }
diff --git a/packages/llms/vitest.config.ts b/packages/llms/vitest.config.js
similarity index 100%
rename from packages/llms/vitest.config.ts
rename to packages/llms/vitest.config.js