59ms: anatomy of a dev cold start

(The native Rust runtime is an experimental track — v0.1's june dev is the Bun/Node host. These numbers are why the track exists.)

We benchmarked our Rust dev runtime's cold start — process spawn to first HTML byte — and then took it apart. Three cuts, all measured (medians, reproducible scripts in the repo):

cut	before	after
listen-early (dev scripts off the critical path)	~100ms blocking	3ms to listening
V8 startup snapshot (Web globals baked into the heap)	24.4ms	5µs
React vendors in the snapshot's module map	98ms	18ms

End to end: 244ms → 59ms on a hello-world page, with the remaining budget split between process spawn (~10ms) and first-render JIT (~30ms) — the latter is V8 physics for unbundled dev, and the bundled production path has already measured 22ms.

The honest caveats: one dev machine, medians not marketing minimums, and next dev/Vite comparisons are class-level, not same-app shootouts yet. Benchmark rigor is its own roadmap item.

One number we did not expect: rebuilding a worker isolate after a file edit dropped from 137ms to 16ms, which is what makes push-based HMR (the server re-renders and pushes the diff over the live channel) feel instant.