cfw-api-startup-optimization

Use the upload timing workflow or the local timing script with a sample size of at least 10 to get min, max, median, and p90 stats. Startup time has high variance, so single runs are noise; compare strictly serial alternating A/B blocks rather than concurrent runs.

Error 10021 means script startup exceeded the 1-second CPU time limit during Cloudflare's validation. Startup time covers V8 parsing plus all top-level code execution such as Zod schema construction, so reducing top-level evaluation work is the fix, not minification.

No. Minification shrinks bundle bytes but startup CPU time stays identical because V8 performs the same top-level evaluation work. It was measured in PR #21204 with no startup improvement, though it remains useful for upload size.

Run wrangler check startup against the already-built bundle, aggregating 10 serial runs into cpuprofiles. Map minified frames through the build sourcemap and aggregate self time by npm package, since raw subtree names are misleading.

Route extraction to separate workers saved about 100ms, subpath imports replaced barrel imports for tree-shaking, and AOT precompilation of buildZodGuard with zod-compiler cut the median by about 41ms. Dynamic import of the router was measured and removed after showing no startup benefit.

Avoid it for route handlers that must register synchronously, since it breaks OpenAPI schema generation and causes miniflare test hangs. It works only for routes hidden from OpenAPI, such as the backfill route in cfw-api.