Using explicitEnvironmentVariables tries to import _app/env.js despite not emitting it.

[minht11]

Describe the bug

I am using new explicitEnvironmentVariables option, with 2 static variables.

Generate index.html script includes import for _app/env.js, despite it not existing.

__sveltekit_1fs6yae = {
						base: "",
						env: null
					};

					const element = document.currentScript.parentElement;

					import("/_app/env.js").then(({ env }) => {
						__sveltekit_1fs6yae.env = env;

						Promise.all([
							import("/_app/immutable/entry/start.DBxPQlil.js"),
							import("/_app/immutable/entry/app.D9hp4Ypm.js")
						]).then(([kit, app]) => {
							kit.start(app, element, {
									node_ids: [0, 13],
									data: [null,null],
									form: null,
									error: null
								});
						});
					});
				}

service worker file includes importScripts(/_app/env.script.js) but that file also doesn't exist.

Variables themselves are inlined correctly it just that import is also added into html/service worker entry points.

interestingly vite preview works fine and does not contain import("/_app/env.js") but actual source output does.

Reproduction

1. Goto https://stackblitz.com/edit/sveltejs-kit-template-default-597qc6h8?file=.svelte-kit%2Foutput%2Fprerendered%2Fpages%2Findex.html
2. Run pnpm run build.
3. Go to .svelte-kit/output/prerendered/pages/index.html.
4. Observe entry script imports env.js despite it not existing.

Logs

System Info

System:
    OS: macOS 26.5.1
    CPU: (10) arm64 Apple M4
    Memory: 315.45 MB / 32.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 26.2.0 - /Users/justinas/.proto/tools/node/26.2.0/bin/node
    Yarn: 4.6.0 - /Users/justinas/.proto/shims/yarn
    npm: 11.13.0 - /Users/justinas/.proto/tools/node/26.2.0/bin/npm
    pnpm: 11.5.2 - /Users/justinas/.proto/tools/pnpm/11.5.2/shims/pnpm
  Browsers:
    Brave Browser: 148.1.90.128
    Chrome: 149.0.7827.53
    Chrome Canary: 151.0.7881.0
    Firefox: 151.0.1
    Safari: 26.5
    Safari Technology Preview: 26.0
  npmPackages:
    @sveltejs/adapter-static: 3.0.10 => 3.0.10 
    @sveltejs/kit: 2.63.1 => 2.63.1 
    svelte: 5.56.2 => 5.56.2 
    vite: 8.0.16 => 8.0.16

Severity

serious, but I can work around it

Additional Information

No response

[Nic-Polumeyv]

Hit this in production today on an adapter-static site. Every prerendered page imports /_app/env.js, the host answers with the SPA fallback HTML, and hydration dies on the MIME error before any user code runs.

Been working on this for a few hours; PR soon. I think the solution is to skip the deferral when no dynamic public env is actually in play, and emit env.js/env.script.js as prerender output for the genuinely dynamic case.