Guard createWebpackBuildPromise against early runWebpack rejection

Attach a catch handler to the async runWebpack call so early setup
errors (e.g., failing dynamic imports) properly reject the outer
promise instead of hanging. Mirrored the same protection in the
development single-build path to surface failures deterministically.

This prevents silent timeouts during CI and improves failure signaling
without altering build outputs.

Author: PeterDaveHello

build.mjs

@@ -544,21 +544,29 @@ async function finishOutput(outputDirSuffix, sourceBuildDir = outdir) {
 async function build() {
   await deleteOldDir()
   function createWebpackBuildPromise(isWithoutKatex, isWithoutTiktoken, minimal, tmpDir, suffix) {
-    return new Promise((resolve, reject) =>
-      runWebpack(isWithoutKatex, isWithoutTiktoken, minimal, tmpDir, async (err, stats) => {
-        if (err || (stats && typeof stats.hasErrors === 'function' && stats.hasErrors())) {
-          console.error(err || stats.toString())
-          reject(err || new Error('webpack error'))
-          return
-        }
-        try {
-          await finishOutput(suffix, tmpDir)
-          resolve()
-        } catch (copyErr) {
-          reject(copyErr)
-        }
-      }),
-    )
+    return new Promise((resolve, reject) => {
+      const ret = runWebpack(
+        isWithoutKatex,
+        isWithoutTiktoken,
+        minimal,
+        tmpDir,
+        async (err, stats) => {
+          if (err || (stats && typeof stats.hasErrors === 'function' && stats.hasErrors())) {
+            console.error(err || stats.toString())
+            reject(err || new Error('webpack error'))
+            return
+          }
+          try {
+            await finishOutput(suffix, tmpDir)
+            resolve()
+          } catch (copyErr) {
+            reject(copyErr)
+          }
+        },
+      )
+      // runWebpack is async; catch early rejections (e.g., failed dynamic imports)
+      if (ret && typeof ret.then === 'function') ret.catch(reject)
+    })
   }
   if (isProduction && !isAnalyzing) {
     const tmpFull = `${outdir}/.tmp-full`
@@ -580,8 +588,8 @@ async function build() {
     return
   }
 
-  await new Promise((resolve, reject) =>
-    runWebpack(false, false, false, outdir, async (err, stats) => {
+  await new Promise((resolve, reject) => {
+    const ret = runWebpack(false, false, false, outdir, async (err, stats) => {
       if (err || (stats && typeof stats.hasErrors === 'function' && stats.hasErrors())) {
         console.error(err || stats.toString())
         reject(err || new Error('webpack error'))
@@ -593,8 +601,9 @@ async function build() {
       } catch (e) {
         reject(e)
       }
-    }),
-  )
+    })
+    if (ret && typeof ret.then === 'function') ret.catch(reject)
+  })
 }
 
 build().catch((e) => {