Book: Kotlin and Java to TypeScript — A Bridge for JVM Developers Also by me: The TypeScript Library — the 5-book collection My project: Hermes IDE | GitHub — an IDE for developers who ship with Claude Code and other AI coding tools Me: xgabriel.com | GitHub A Kotlin engineer ports their first non-trivial service to Node. The handler launches three calls in parallel, the request times out, and the engineer expects the in-flight work to stop. It does not. Two of the three downstream calls finish ten seconds later, write to the database, and emit a metric for a request whose response was already a 504. In Kotlin, that bug does not exist. Every coroutineScope and every launch belongs to a parent. The runtime cancels every child recursively and atomically when the parent is cancelled. It is not a library feature. It is the central design decision of kotlinx.coroutines . The Kotlin docs call it structured concurrency . JavaScript has none of this. A Promise does not have cancel() .…