Invalid export 'a' error from layout.server.ts/layout.ts during build process above 2.22.2

Describe the bug

We're getting an error about invalid exports in layout files that appears to be a false positive. We have no problem in development mode, only in build.
We got this error when we upgrade SvelteKit from 2.22.2 to above, even the latest 2.27.1, we are getting this error.

Reproduction

Making a reproduction is very hard since we really don't know how to reproduce, we have literally no idea...

Logs

The error occurs during the build process:

node:internal/event_target:1101
  process.nextTick(() => { throw err; });
                           ^
Error: Invalid export 'a' in src/routes/+layout.server.ts (valid exports are load, prerender, csr, ssr, trailingSlash, config, or anything with a '_' prefix)
    at validate (file:///application/node_modules/.pnpm/@sveltejs+kit@2.27.0_@sveltejs+vite-plugin-svelte@5.1.1_svelte@5.37.3_vite@6.3.5_@types+node@_f7pbfpiqtqavra6y44eihmr6gu/node_modules/@sveltejs/kit/src/utils/exports.js:21:10)
    at PageNodes.validate (file:///application/node_modules/.pnpm/@sveltejs+kit@2.27.0_@sveltejs+vite-plugin-svelte@5.1.1_svelte@5.37.3_vite@6.3.5_@types+node@_f7pbfpiqtqavra6y44eihmr6gu/node_modules/@sveltejs/kit/src/utils/page_nodes.js:29:5)
    at analyse_page (file:///application/node_modules/.pnpm/@sveltejs+kit@2.27.0_@sveltejs+vite-plugin-svelte@5.1.1_svelte@5.37.3_vite@6.3.5_@types+node@_f7pbfpiqtqavra6y44eihmr6gu/node_modules/@sveltejs/kit/src/core/postbuild/analyse.js:236:8)
    at analyse (file:///application/node_modules/.pnpm/@sveltejs+kit@2.27.0_@sveltejs+vite-plugin-svelte@5.1.1_svelte@5.37.3_vite@6.3.5_@types+node@_f7pbfpiqtqavra6y44eihmr6gu/node_modules/@sveltejs/kit/src/core/postbuild/analyse.js:115:4)
    at async MessagePort.<anonymous> (file:///application/node_modules/.pnpm/@sveltejs+kit@2.27.0_@sveltejs+vite-plugin-svelte@5.1.1_svelte@5.37.3_vite@6.3.5_@types+node@_f7pbfpiqtqavra6y44eihmr6gu/node_modules/@sveltejs/kit/src/utils/fork.js:23:16)

In file applications/web/.svelte-kit/output/server/entries/pages/_layout.server.ts.js we can see the invalid export:

export {
  load$4 as a,
  load$3 as b,
  load$2 as c,
  load$1 as d,
  load as e,
  load$5 as l,
  load$6 as load,
  ssr as s
};

System Info

System:
    OS: macOS 15.5
    CPU: (16) arm64 Apple M3 Max
    Memory: 300.17 MB / 48.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.18.0 - ~/.volta/tools/image/node/22.18.0/bin/node
    npm: 10.9.3 - ~/.volta/tools/image/node/22.18.0/bin/npm
    pnpm: 10.13.1 - ~/.volta/bin/pnpm
    bun: 1.2.19 - /opt/homebrew/bin/bun
  Browsers:
    Chrome: 138.0.7204.184
    Safari: 18.5
  npmPackages:
    @sveltejs/adapter-node: ^5.2.13 => 5.2.13 
    @sveltejs/kit: 2.27.1 => 2.27.1 
    @sveltejs/vite-plugin-svelte: ^5.1.1 => 5.1.1 
    svelte: ^5.37.0 => 5.37.3 
    vite: ^6.3.5 => 6.3.5

Severity

blocking an upgrade

Additional Information

There is a high chance this issue will directly be closed since there is no reproduction but we are facing this error since a month and many developers on our team tried to fix this issue without any success by reviewing all of our layout files but nothing anormal was found.
Even claude sonnet model tried things without success.

Maybe somebody faced the same error or somebody from the SvelteKit core team can help us to test some modifications.

Start at src/utils/exports.js, src/utils/page_nodes.js, and src/core/postbuild/analyse.js from the stack trace, then inspect applications/web/.svelte-kit/output/server/entries/pages/_layout.server.ts.js and its generated exports. Compare the generated aliases with the validation rules and use a reproducible build to confirm the invalid-export error no longer appears for valid layout files.