feat(cloudflare/vite): runner-mode dev with HMR via Bun.serve front-proxy

[Mkassabov]

Wire Cloudflare.Vite into bun alchemy dev so SPA projects get a working dev loop with Vite HMR. SSR projects (cloudflare-vite-plugin virtual entry) detected at runtime and gated until the workerd-side runner pieces are wired through serveVite.

Before: bun alchemy dev crashed with BundleError: Failed to find real path for bundle: undefined for any Cloudflare.Vite resource because LocalWorkerProvider had no Vite branch.

After:

import * as Cloudflare from "alchemy/Cloudflare";
const Web = Cloudflare.Vite("Web", {
  rootDir: "./web",
  compatibility: { flags: ["nodejs_compat"] },
  assets: {
    config: {
      htmlHandling: "auto-trailing-slash",
      notFoundHandling: "single-page-application",
    },
  },
});

$ bun alchemy dev --profile <profile>
✓ Web (Cloudflare.Worker) updated
{ webUrl: "http://web-...localhost:1337" }

Browser loads the SPA via the workerd LocalProxy → Bun.serve front-proxy → Vite middleware. Vite's HMR runs on a dedicated port the browser connects to directly. Editing web/src/main.ts hot-updates without a page refresh. The HMR port is persisted across bun --watch reloads so the browser auto-reconnects when the dev process restarts.

A small auto-accept Vite plugin appends if (import.meta.hot) import.meta.hot.accept() to user .ts/.js/.tsx/.jsx files outside node_modules that don't already mention import.meta.hot — boilerplate-free hot-update for plain SPAs.

Architecture

• Cloudflare/Local/Vite/ViteDev.ts — spawns Vite in middleware mode with a dedicated HMR port; control HTTP server for SSR module-graph snapshots.
• Cloudflare/Local/Vite/FrontProxy.ts — Bun.serve listener that drives Vite's connect middleware against a real Writable shim (so sirv's createReadStream(file).pipe(res) for /@fs/ works) and falls through to workerd for SSR.
• Cloudflare/Local/Vite/AutoAcceptPlugin.ts — auto-injects import.meta.hot.accept().
• Cloudflare/Local/Vite/HostWorker.ts + ModuleSnapshot.ts — workerd-side runner-mode pieces (worker_loader bootstrap + SSR module-graph walk). Type-clean but currently gated; activation needs Runtime/Bindings exposed from cloudflare-runtime/RuntimeServices.
• Cloudflare/Local/Sidecar.ts + SidecarHandlers.ts — new serveVite RPC. Hash-keyed reuse map keeps the same Vite scope alive across bun --watch reloads on POSIX.
• Cloudflare/Workers/LocalWorkerProvider.ts — branches on props.vite.

Windows fixes that came out of testing

• Sidecar/Lock.ts — Date.now() → new Date() on win32 (Bun fs.utimes EINVAL on millis); bounded retry on lock conflict to absorb the bun --watch reload race.
• SidecarServer.ts — exit silently on LockError(Conflict) instead of dumping a stack trace.
• Sidecar/RpcClient.ts — drop detached: true on win32. DETACHED_PROCESS allocates a console window regardless of windowsHide. Trade-off: sidecar dies with parent on Windows (Vite restarts on alchemy.run.ts edits), but the persisted HMR port lets the browser auto-reconnect.
• Util/PlatformServices.ts — patch child_process.spawn/etc. and Bun.spawn/spawnSync to default windowsHide: true on win32.
• bin/exec.ts — propagate --profile to subprocesses via ALCHEMY_PROFILE env. ConfigProvider override only applied to the local Effect runtime; the sidecar saw "default" profile and prompted for Cloudflare auth.
• Vite/ViteDev.ts — cacheDir set to <root>/.alchemy/vite (absolute via path.resolve). Vite's default cache lives under node_modules/.vite/deps, which sits inside a bun link-ed alchemy symlink — bun --watch follows the symlink and reloads the dev process every time Vite re-optimizes deps.

Vite 8 compatibility

FrontProxy.ts shim is a real Writable and implements the full ServerResponse surface Vite 8 + sirv exercise: setHeader/getHeader/removeHeader/appendHeader/getHeaders/getHeaderNames/hasHeader/writeHead/flushHeaders plus stream _write. appendHeader is required for Vite 8's Vary: Sec-Fetch-Dest and stream-piping is required for sirv to serve env.mjs etc. with the right MIME type.