Let me start with a confession: I have been writing concurrent code since the only tool in the box was a mutex and a prayer. After a decade of Swift I feel suspicion of any code that touches two threads and claims to be fine.
So when Swift 6 showed up promising to prove my concurrency correct at compile time, I had two reactions at once. The grizzled half of me said "sure, kid." The other half — the half that has spent actual weekends chasing a heisenbug that only reproduced on a customer's M1 under sync load — said "...please. Please be real."
This is the story of moving Ditto Edge Studio — a SwiftUI debug-and-query tool for the Ditto edge database — to Swift 6's strict concurrency mode. It's a real app: SQLCipher persistence, an embedded MCP server, a SpriteKit presence graph, live sync over Bluetooth and WebSocket. Not a to-do list. The kind of app where concurrency bugs hide in the cracks and wait for a demo.
Spoiler: it was worth it. It was also more work than the WWDC talk implied, and the most valuable thing the compiler did happened in the one place I told it to stop looking. Let me show you.
First, the Wall: A Dependency That Wasn't Coming to Swift 6
