Real-Time on the Web

The owner wants the pin moving

A dog walk is LIVE. Somewhere out there, a walker's phone is producing a new GPS position every few seconds, and the owner staring at the app wants to see that pin crawl across the map as it happens — not refresh and hope. Everything you've built through module 12 was ask once, answer once: a curl request, a JSON response, done. That shape doesn't fit a moving dog.

The iOS side of this exact feature (Services/LiveTracker.swift, if you've seen that course) opens one socket per booking and watches it stream. This module builds the SERVER half of that same feature — the piece that decides who's allowed to listen, and pushes the fix out to everyone who is.