fix: ensure version is defined when using $app/env with explicit env vars

[Nic-Polumeyv]

When experimental.explicitEnvironmentVariables is enabled, $app/environment throws and apps import from $app/env instead. $app/env re-exports version from internal.js (export const version = __SVELTEKIT_APP_VERSION__), but unlike $app/environment it never references import.meta.hot, so Vite doesn't force its client to load. If $app/env is imported before the Vite client has loaded, version evaluates while the define is missing and the browser throws:

ReferenceError: __SVELTEKIT_APP_VERSION__ is not defined

This happens when $app/env is imported early, e.g. from hooks.client.js. Importing it from a route component is too late to hit it, since the client is already up by then, which is why it's intermittent. I ran into it in a real app after enabling experimental.explicitEnvironmentVariables.

It came in with #15934, which moved version onto the __SVELTEKIT_APP_VERSION__ define and added import.meta.hot to $app/environment, but not to the newly split $app/env.

The fix mirrors $app/environment. I left that file's import.meta.hot in place to keep this minimal, though it's now redundant with this one.

Added a regression test in options-2: an early $app/env import in hooks.client.js plus a load of the page. It fails on main (the app never finishes hydrating) and passes with this change.

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[Nic-Polumeyv]

The two failing jobs look unrelated to this change. test-kit (20) crashed at the Node level (Assertion failed: (req_wrap_async) != nullptr, exit 129) and test-kit (22) timed out on a remote-functions e2e test, while 18, 24 and all cross-browser runs pass. This PR only adds import.meta.hot to $app/env, so I don't think it's related, but happy to rebase or re-run if that helps.

[Nic-Polumeyv]

Added a regression test in options-2 and pinned the exact trigger: the error fires when $app/env is imported before the Vite client loads (e.g. from hooks.client.js); a route-component import is too late to hit it. Verified locally that the test fails on main and passes with this change. (Updating an earlier note of mine that said a deterministic test wasn't feasible, it is.)

[teemingc]

I wonder if a fix such as https://github.com/sveltejs/kit/pull/15574/changes#diff-a7244013c14e3925b24a2faf96dc33f01fae957ae2fa1a89a96fba3ee90be886R646 would be more fool proof. This isn’t the first time we’ve run into this issue and it could happen again depending on the order or presence of imported modules.

[teemingc]

Thanks!