Show HN: AI Subroutines – Run automation scripts inside your browser tab

rtrvr.ai introduced AI Subroutines, which turn a recorded browser task into a callable tool and replay it at zero token cost and zero LLM inference delay. The script runs inside the active tab, reusing auth, CSRF, TLS sessions, and signed headers; recording trims about 300 requests to about 5 and falls back to DOM-only when GraphQL operation IDs are volatile. The part to watch is batching: one LLM call can assign parameters for a 500-row sheet and launch 500 subroutines.

Why it matters: This clears HKR-H/K/R: the hook is zero-token browser automation, the post gives concrete mechanics (300→5 requests, DOM fallback, 500-row fan-out), and it hits agent reliability/cost pain. Kept to mid-featured because it is a single-company Show HN post, not a market-wide event.