Wires a writ_create_monitor monitor's change_detected event to an action. action='workflow' runs a saved workflow when the monitored page changes; action='notify' sends a notification to channels + recipients the account has configured; action='ai_task' wakes an AI agent with a task prompt: the agent opens the monitored page in a cloud browser, sees what changed (diff + extracted values) and works the prompt autonomously (channels/recipients also notify when it finishes). A price watch takes threshold: the action then runs once, when a check reads a price at or below it (threshold_op picks the side), not on every change. Buying at the price, in order: 1) writ_create_monitor reads the price; 2) writ_record_website or writ_browser_use, then writ_browser_save, record the checkout up to the order page, with the product, quantity and shipping as inputs where they vary, an extract of the total, and the order button never pressed (its selector kept); 3) writ_run_workflow with mutation_mode='dry_run' rehearses it once, to end on the order page and return the total (safe to rehearse only a checkout recorded this way: an older one may hold the order click); 4) action='workflow' + that workflow + buy (payment {kind, ref} from writ_payment, total_selector, commit_selector = that button (Writ clicks it live), fallback_ai_session: true); 5) the fallback, ONLY when the checkout can't be recorded or its rehearsal fails (bot wall, a checkout that won't replay, a login the persona can't hold): action='ai_task' with a prompt naming what to buy and the same buy; an AI PURCHASE session browses to the order page and hands over to Writ's confirmed checkout. Either way it is saved as a REHEARSAL (dry run) until the user turns purchases on in the Writ app, and a person confirms each purchase unless an auto-confirm rule they set covers automation purchases. The answer's buy.runs_as names the path: recorded_checkout or ai_purchase_session.