feat(agent): add instructions api

packages/page-agent/src/PageAgent.ts

@@ -361,9 +361,40 @@ export class PageAgent extends EventTarget {
 		return systemPrompt
 	}
 
+	/**
+	 * Get instructions from config and format as XML block
+	 */
+	async #getInstructions(): Promise<string> {
+		const { instructions } = this.config
+		if (!instructions) return ''
+
+		const systemInstructions = instructions.system?.trim()
+		const url = await this.pageController.getCurrentUrl()
+		const pageInstructions = instructions.getPageInstructions?.(url)?.trim()
+
+		if (!systemInstructions && !pageInstructions) return ''
+
+		let result = '<instructions>\n'
+
+		if (systemInstructions) {
+			result += `<system_instructions>\n${systemInstructions}\n</system_instructions>\n`
+		}
+
+		if (pageInstructions) {
+			result += `<page_instructions>\n${pageInstructions}\n</page_instructions>\n`
+		}
+
+		result += '</instructions>\n\n'
+
+		return result
+	}
+
 	async #assembleUserPrompt(): Promise<string> {
 		let prompt = ''
 
+		// <instructions> (optional)
+		prompt += await this.#getInstructions()
+
 		// <agent_state>
 		//  - <user_request>
 		//  - <step_info>

packages/page-agent/src/config/index.ts

@@ -42,6 +42,24 @@ export interface AgentConfig {
 	 */
 	customTools?: Record<string, PageAgentTool | null>
 
+	/**
+	 * Instructions to guide the agent's behavior
+	 */
+	instructions?: {
+		/**
+		 * Global system-level instructions, applied to all tasks
+		 */
+		system?: string
+
+		/**
+		 * Dynamic page-level instructions callback
+		 * Called before each step to get instructions for the current page
+		 * @param url - Current page URL (window.location.href)
+		 * @returns Instructions string, or undefined/null to skip
+		 */
+		getPageInstructions?: (url: string) => string | undefined | null
+	}
+
 	// lifecycle hooks
 	// @todo: use event instead of hooks