fix(vite-plugin): keep Miniflare alive when a build runs during serve

[1rgs]

What / why

The plugin uses buildEnd as its signal that the dev server is closing, and disposes the Miniflare instance there:

https://github.com/cloudflare/workers-sdk/blob/main/packages/vite-plugin-cloudflare/src/plugins/dev.ts#L58-L69

Vite's experimental.bundledDev runs a Rolldown build pass during serve, so buildEnd fires while the dev server is still live. Miniflare gets torn down mid-serve and every subsequent request fails:

[vite] Internal server error: Expected `miniflare` to be defined
    at get miniflare (@cloudflare/vite-plugin/dist/index.mjs)
    at cloudflarePreMiddleware (@cloudflare/vite-plugin/dist/index.mjs)

With NODE_DEBUG=@cloudflare:vite-plugin the sequence is unambiguous:

Creating new Miniflare instance
Miniflare is ready
buildEnd: disposing        <-- during serve, not on close
... next request -> 500

Reproduces on both the currently pinned 1.37.2 and latest 1.45.1 (with matching wrangler), so it isn't version lag — the dev architecture just assumes a pure module-runner serve rather than a build-during-serve.

Why bundledDev matters here (i.e. why fix this rather than avoid the flag)

Vite's unbundled dev server is optimised for the common case: the browser is on the same machine as the dev server, so one HTTP request per module is essentially free.

Our dev servers aren't local to the browser. Each runs inside a remote sandbox, and the browser reaches it through a Cloudflare Worker and a tunnel. Every module request is a full cross-network round trip, and the app is ~1000 modules — so a cold page load issues ~1000 sequential-ish round trips before it renders. Requests dominate; transform time is noise.

experimental.bundledDev is the direct fix for that shape: Rolldown bundles the graph and the dev server ships a handful of chunks instead of a thousand modules, while keeping HMR. It collapses the request count by orders of magnitude, which is exactly the axis that hurts when the dev server is behind a Worker.

This isn't a niche setup, and it's one Cloudflare users are likely to hit more, not less: remote/cloud dev environments, Codespaces-style sandboxes, and any workflow where the Vite dev server sits behind a Worker or tunnel all have the same profile. Today the combination of @cloudflare/vite-plugin + experimental.bundledDev is unusable — not slow, but 500 on every request — so the flag can't be evaluated at all by anyone using this plugin.

The fix is also small and independent of bundledDev itself: it just stops the plugin from conflating "a build finished" with "the dev server closed". That conflation is arguably wrong regardless of this flag — any plugin or future Vite feature that triggers a build during serve would hit the same teardown.

The change

During serve, dispose Miniflare from a patched server.close instead of from buildEnd. This mirrors the existing server.restart patch in index.ts, so the mechanism should look familiar:

https://github.com/cloudflare/workers-sdk/blob/main/packages/vite-plugin-cloudflare/src/index.ts#L93-L105

Preserved behaviour:

• production builds — unchanged (buildEnd still disposes when command !== "serve")
• dev-server restarts — Miniflare still stays warm (the !isRestartingDevServer guard moved with the disposal)
• forceful exits (ctrl+C) — still covered by the existing exit handler, which the code comments already call out as the reason buildEnd alone was never sufficient

Test

packages/vite-plugin-cloudflare/src/__tests__/bundled-dev-dispose.spec.ts starts a real dev server, invokes the cloudflare plugins' buildEnd hooks (exactly what a bundledDev build pass does), and asserts the server still serves. It fails on main with Expected \miniflare` to be definedand passes with this change. Modeled on the existinghmr-events.spec.ts`.

Driving the hook directly (rather than enabling bundledDev in the fixture) keeps the test deterministic and independent of an experimental Vite flag's internals — it pins the actual invariant: a buildEnd during serve must not dispose Miniflare.

Validation beyond the unit test

Applied the equivalent change to the built plugin inside a large real app (~1000 modules, React + TanStack Router, Worker + SPA) and ran it with experimental.bundledDev enabled:

	before	after
GET /	500 Expected \miniflare` to be defined`	200, real app HTML
GET /src/main.tsx	500	200
repeated requests	500	stable 200

Unrelated note in case it's useful to maintainers: with bundledDev there's also a separate non-fatal TypeError: Cannot read properties of undefined (reading 'config') from @vitejs/plugin-react-swc's transformIndexHtml — different repo, and it doesn't block serving once this fix is in.

Changeset

Patch for @cloudflare/vite-plugin.

---

• Tests
  • Tests included/updated
  • Automated tests not possible - manual testing has been completed as follows:
  • Additional testing not necessary because:
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: bug fix

[changeset-bot]

🦋 Changeset detected

Latest commit: a2d11e7

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@cloudflare/vite-plugin	Patch

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[workers-devprod]

Codeowners approval required for this PR:

• ✅ @cloudflare/wrangler

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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[pkg-pr-new]

@cloudflare/autoconfig

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wrangler

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commit: a2d11e7

[jamesopstad]

Thanks for the PR! I'm working on getting some new APIs added in Vite that would enable us to remove the server patching (vitejs/vite#22913) but this is a good workaround for now. I pushed a couple of commits.

We also need to ensure that HTML files are served correctly in experimental.bundledDev. I'll try and get a PR up for that today.

[workers-devprod]

Codeowners reviews satisfied