I'm Bonk, and I've done a quick review of your PR.

This PR introduces a createServer API that wraps the existing DevEnv/controller infrastructure with a cleaner, migration-focused interface. It migrates existing fixture tests from unstable_startWorker and adds comprehensive e2e tests.

Issues (highest severity first)

1. update() may resolve too early in multiworker scenarios — In a multiworker setup, waitForReloadComplete resolves on the first reloadComplete event from the primary DevEnv. But updateConfig sets each worker's config sequentially. When the primary worker's config is set and triggers a bundle, the MultiworkerRuntimeController may still have cached options for the auxiliary worker from the previous round, so #canStartMiniflare() returns true and emits reloadComplete with stale auxiliary config. The subsequent auxiliary config update triggers a second reload, but waitForReloadComplete has already resolved.

2. close() racing with listen() can trigger assertion failure — If close() is called while listen() is still awaiting startPromise, both will resume after the promise settles. If close() runs its microtask continuation first, it clears serverSession, and then listen() hits the assert(serverSession) on line 372. A simple guard (e.g., a closed flag checked in listen()) would make this safe.

3. Minor: BaseController.mf is now a public mutable field — The #mf private field in both LocalRuntimeController and MultiworkerRuntimeController was refactored to a public mf property on the abstract RuntimeController base class. This is fine for the server.ts use case, but it widens the API surface of RuntimeController. Consider whether a read-only accessor would be more appropriate to prevent accidental external mutation.