perf(@angular/build): avoid sharding intermediate files under worker surplus in i18n inliner

packages/angular/build/src/tools/i18n/i18n-inliner.ts

@@ -66,12 +66,12 @@ const SMALL_FILE_FLOOR_BYTES = 100 * 1024;
 
 /**
  * Ratio of the maximum file size in a window to consider a file "dominant".
- * Files within 70% of the largest file are sharded across all workers for maximum concurrency.
+ * Files within 70% of the largest file are sharded across bounded workers for concurrency.
  */
 const DOMINANT_FILE_RATIO = 0.7;
 
 /**
- * Maximum number of worker threads to allocate concurrently for a single dominant file.
+ * Maximum number of worker threads to allocate concurrently across dominant files.
  * Capping concurrency on dominant files (which hold large AST and sourcemap trees)
  * prevents V8 heap and RSS explosion on machines with high CPU core counts.
  */
@@ -520,6 +520,20 @@ export class I18nInliner {
     // while small files act as gap fillers near the window barrier to prevent tail stragglers.
     sortedFiles.sort((a, b) => b.fileSize - a.fileSize);
 
+    const dominantThreshold = Math.max(SMALL_FILE_FLOOR_BYTES, maxFileSize * DOMINANT_FILE_RATIO);
+    let dominantCount = 0;
+    for (const { fileSize } of sortedFiles) {
+      if (fileSize >= dominantThreshold) {
+        dominantCount++;
+      } else {
+        break;
+      }
+    }
+    const dominantTargetWorkers =
+      dominantCount > 0
+        ? Math.max(1, Math.min(workerCount - 1, Math.floor(MAX_DOMINANT_WORKERS / dominantCount)))
+        : 1;
+
     const workerTasks: Promise<void>[] = [];
 
     for (const { filename, entries, codeFile, fileSize } of sortedFiles) {
@@ -535,13 +549,16 @@ export class I18nInliner {
       } else if (fileSize < SMALL_FILE_FLOOR_BYTES) {
         // Small chunks (< 100 KB): process all locales in 1 batch to eliminate IPC overhead
         localesPerBatch = entries.length;
-      } else if (fileSize >= maxFileSize * DOMINANT_FILE_RATIO) {
+      } else if (fileSize >= dominantThreshold) {
         // Dominant file(s) with multiple files: shard across bounded workers while always reserving
         // at least one worker to process smaller chunks in parallel without starvation.
-        const targetWorkers = Math.max(1, Math.min(workerCount - 1, MAX_DOMINANT_WORKERS));
-        localesPerBatch = Math.max(1, Math.ceil(entries.length / targetWorkers));
+        localesPerBatch = Math.max(1, Math.ceil(entries.length / dominantTargetWorkers));
+      } else if (uncachedByFile.size >= workerCount) {
+        // Worker pool is already saturated by file-level concurrency;
+        // process all locales in a single batch to avoid duplicate parsing and IPC overhead.
+        localesPerBatch = entries.length;
       } else {
-        // Intermediate files: moderate sharding
+        // Intermediate files with idle workers: moderate sharding
         localesPerBatch = Math.max(1, Math.ceil(entries.length / 2));
       }