Limit webpack cache version to output-affecting dimensions

Remove THREAD, WORKERS, and CACHE_COMP from Webpack filesystem cache
version to avoid unnecessary invalidations across machines/CI runners.
This keeps BUILD_CACHE_COMPRESSION effective via the compression field
without affecting cache validity.

Why: Worker count, thread toggle, and cache compression do not change
module outputs; including them in the version reduces cross-run cache
hit rates. Retain PROD in the version since prod/dev impacts outputs.

Author: PeterDaveHello

build.mjs

@@ -138,12 +138,9 @@ async function runWebpack(isWithoutKatex, isWithoutTiktoken, minimal, sourceBuil
     cache: {
       type: 'filesystem',
       name: `webpack-${variantId}`,
-      version: JSON.stringify({
-        THREAD: enableThread,
-        WORKERS: threadWorkers,
-        CACHE_COMP: cacheCompressionOption ?? false,
-        PROD: isProduction,
-      }),
+      // Only include dimensions that affect module outputs to avoid
+      // unnecessary cache invalidations across machines/CI runners
+      version: JSON.stringify({ PROD: isProduction }),
       // default none; override via BUILD_CACHE_COMPRESSION=gzip|brotli
       compression: cacheCompressionOption ?? false,
       buildDependencies: {