It started at midnight I had 24 hours, a free Replit subscription, and an idea: what if I could build something like Miro — but actually understand every line of code in it? That's how CollabCanvas was born. A real-time collaborative whiteboard where multiple users can draw, drop sticky notes, build flowcharts, and see each other's cursors move live — all synced instantly over WebSockets. I'm a third-year AI & Data Science student, and most of my projects live in Python and ML pipelines. So building a full-stack multiplayer canvas app in a day was genuinely outside my comfort zone. This is the story of how it went. The core problem I had to solve first Multiplayer sync sounds simple until you actually build it. The hard part isn't sending a canvas update — it's figuring out what to send. I tried syncing the full Fabric.js canvas JSON on every change. It worked, but at 30+ objects it became sluggish. The fix was delta syncing — only emitting the changed object's state, not the entire canvas.…