Harden env flags and simplify CPU detection

Treat 'false/no/off/0' as disabled for BUILD_PARALLEL and BUILD_THREAD
while keeping default enabled when unset. Replace defensive cpu count
logic with os.cpus().length guarded by try/catch. This aligns behavior
with documented defaults and improves robustness without changing
outputs.

Author: PeterDaveHello

build.mjs

@@ -14,12 +14,19 @@ const outdir = 'build'
 const __dirname = path.resolve()
 const isProduction = process.argv[2] !== '--development' // --production and --analyze are both production
 const isAnalyzing = process.argv[2] === '--analyze'
-const parallelBuild = process.env.BUILD_PARALLEL !== '0'
+// Env helpers
 function parseBooleanEnv(val) {
   if (val == null) return false
   const s = String(val).trim().toLowerCase()
   return !(s === '' || s === '0' || s === 'false' || s === 'no' || s === 'off')
 }
+function isDisabledEnv(val) {
+  if (val == null) return false
+  const s = String(val).trim().toLowerCase()
+  return s === '' || s === '0' || s === 'false' || s === 'no' || s === 'off'
+}
+// Default: parallel build ON unless explicitly disabled
+const parallelBuild = !isDisabledEnv(process.env.BUILD_PARALLEL)
 const isWatchOnce = parseBooleanEnv(process.env.BUILD_WATCH_ONCE)
 // Cache compression control: default none; allow override via env
 function parseCacheCompressionOption(envVal) {
@@ -33,9 +40,8 @@ function parseCacheCompressionOption(envVal) {
 const cacheCompressionOption = parseCacheCompressionOption(process.env.BUILD_CACHE_COMPRESSION)
 let cpuCount = 1
 try {
-  const cpuInfo = os.cpus && os.cpus()
-  const len = Array.isArray(cpuInfo) ? cpuInfo.length : 0
-  cpuCount = Number.isInteger(len) && len > 0 ? len : 1
+  // os.cpus() returns an array in Node.js; guard with try/catch for portability
+  cpuCount = Math.max(1, os.cpus().length || 1)
 } catch {
   cpuCount = 1
 }
@@ -70,8 +76,8 @@ if (process.env.BUILD_POOL_TIMEOUT) {
     )
   }
 }
-// Enable threads by default; allow disabling via BUILD_THREAD=0
-const enableThread = process.env.BUILD_THREAD !== '0'
+// Enable threads by default; allow disabling via BUILD_THREAD=0/false/no/off
+const enableThread = !isDisabledEnv(process.env.BUILD_THREAD)
 
 async function deleteOldDir() {
   await fs.rm(outdir, { recursive: true, force: true })