fix: eagerly initialise dynamic env vars from process.env at module-eval time

[elliott-with-the-longest-name-on-github]

closes #14286

Dynamic $app/env values are normally populated when Server.init() calls set_env(). The problem is that instrumentation.server.js deliberately runs before Server.init(), so importing $app/env there gives you undefined. More subtly, instrumentation can share a chunk with application code and cause that code to evaluate early too, permanently capturing those undefined values at module scope.

Basically, instrumentation should run before the application, but not before the minimum runtime state it is allowed to observe exists.

This adds an environment initializer to builder.instrument(). Adapters provide the final env module location and generate the small platform-specific initializer; Kit handles the relative import, imports it before instrumentation, and only then dynamically imports the application entrypoint. The same ordering now applies in dev and preview.

The official adapters initialize from their native runtime source:

• Node, Vercel serverless and Netlify serverless use process.env
• Cloudflare uses env from cloudflare:workers
• Netlify edge uses Deno.env.toObject()

Added tests for generated import paths, custom facades, module evaluation order, filename collisions, and a built adapter-node app reading dynamic env at instrumentation module scope.

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 91afeee:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/91afeeed060aede8c09439926c818ec6f8d297f8

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16303

[changeset-bot]

🦋 Changeset detected

Latest commit: 91afeee

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

This PR includes changesets to release 5 packages

Name	Type
@sveltejs/kit	Patch
@sveltejs/adapter-node	Major
@sveltejs/adapter-cloudflare	Major
@sveltejs/adapter-vercel	Major
@sveltejs/adapter-netlify	Major

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-16303-svelte.vercel.app/

[SobolievOleksii]

Tested this branch against the repro for #16288 (adapter-node + src/instrumentation.server.js): the server crashes at startup —

build/__sveltekit_env_init.js:2
import { set_env } from './env.js';
SyntaxError: The requested module './env.js' does not provide an export named 'set_env'

The facade written in builder.js hardcodes import { set_env } from './env.js' relative to the entrypoint, but for adapter-node build/env.js is the adapter's own runtime helper (export { env, env_prefix, timeout_env }) — and kit's env module with set_env doesn't end up at a stable relative path after the adapter's bundling step. Full details in #16288 (comment) — happy to re-test after an adjustment.

[elliott-with-the-longest-name-on-github]

Yeah, this is still a draft, not ready yet 😅