Harden watch-once callback handling and document symlink behavior

- Normalize watcher callback to a Promise to catch sync throws
  and ensure finalize always runs before exit in watch-once
- Add inline note for resolve.symlinks: false to align with docs

This reduces the chance of partial outputs or silent crashes in
single-run dev builds while preserving existing behavior

Author: PeterDaveHello

build.mjs

@@ -203,6 +203,8 @@ async function runWebpack(isWithoutKatex, isWithoutTiktoken, minimal, sourceBuil
     ],
     resolve: {
       extensions: ['.jsx', '.mjs', '.js'],
+      // Disable symlink resolution for consistent behavior/perf; note this can
+      // affect `npm link`/pnpm workspaces during local development
       symlinks: false,
       alias: {
         parse5: path.resolve(__dirname, 'node_modules/parse5'),
@@ -400,7 +402,8 @@ async function runWebpack(isWithoutKatex, isWithoutTiktoken, minimal, sourceBuil
         err ||
         (stats && typeof stats.hasErrors === 'function' && stats.hasErrors())
       )
-      const ret = callback(err, stats)
+      // Normalize callback return into a Promise to catch synchronous throws
+      const ret = Promise.resolve().then(() => callback(err, stats))
       if (isWatchOnce) {
         const finalize = (callbackFailed = false) =>
           watching.close((closeErr) => {
@@ -410,12 +413,10 @@ async function runWebpack(isWithoutKatex, isWithoutTiktoken, minimal, sourceBuil
             const shouldFail = hasErrors || closeErr || callbackFailed
             process.exit(shouldFail ? 1 : 0)
           })
-        if (ret && typeof ret.then === 'function')
-          ret.then(
-            () => finalize(false),
-            () => finalize(true),
-          )
-        else finalize(false)
+        ret.then(
+          () => finalize(false),
+          () => finalize(true),
+        )
       }
     })
   }