perf(@angular/build): consolidate build worker pools with shared router

[alan-agius4]

Unify isolated per-subsystem worker pools (JavaScriptTransformer, SassService, I18nInliner) into a single singleton WorkerPool routed via dynamic task dispatching (shared-worker-router.ts).

• Reduce active worker threads by 66.7% (24 -> 8 threads), eliminating thread thrashing and reducing kernel system CPU time by 42.3%.
• Implement zero-copy transferable file and translation Blobs, avoiding IPC serialization overhead.
• Add bounded Map caching (fileDataCache, deserializedTranslations) with fileKey and translationKey in the i18n inliner worker isolate, achieving 100% AST and 99.8% translation cache hit rates across locales without memory leaks.
• Standardize discriminated union tasks (InlineI18nFileTask, InlineI18nCodeTask) with zero-allocation synchronous dispatching.

Benchmark 1: Subsystem Benchmark (500 Components, 500 SCSS Stylesheets, 5 Locales / 3,500 operations, 5 iterations)

Metric	Baseline (main)	Consolidated (perf-build-singleton-shared-worker-pool)	Delta / Speedup
Active Worker Threads	24 threads	8 threads	-66.7% threads (-16 threads)
Cold Build Duration (mean)	1,182.0 ms	1,180.5 ms	1.00x faster (-0.1%)
Cold Build Duration (min / max)	1,151.7 ms / 1,228.2 ms	1,156.8 ms / 1,224.2 ms	+5.1 ms / -4.0 ms
P95 Build Latency	1,228.2 ms	1,224.2 ms	-0.3% (-4.0 ms)
Throughput	2,962.4 ops/sec	2,966.1 ops/sec	+0.1% (+3.7 ops/sec)
I18n Inlining Duration (Pure mean)	696.0 ms	217.9 ms	3.19x faster (-68.7%)
I18n Inlining (min / max)	678.7 ms / 730.5 ms	196.4 ms / 243.2 ms	3.46x / 3.00x faster
AST Cache Hit Rate (Subsequent Locales)	0.0% (0 / 2,000)	100.0% (2,000 / 2,000)	100.0% cache hit rate
Translation Cache Hit Rate	0.0% (0 / 2,500)	99.8% (2,495 / 2,500)	99.8% cache hit rate
Process RSS Delta	+2,786.0 MB	+1,519.7 MB	-45.5% (-1,266.3 MB saved)
Final Process RSS	2,842.1 MB	1,576.4 MB	-44.5% (-1,265.7 MB saved)
Kernel System CPU	2,355.1 ms	1,358.3 ms	-42.3% (1.73x less kernel CPU)
Total CPU (User + Kernel)	16,198.8 ms	10,808.7 ms	-33.3% (1.50x CPU efficiency)

Benchmark 2: End-to-End ng build Application Benchmark (500 Components, 500 SCSS Stylesheets, 5 Locales, 5 iterations)

Metric	Baseline (main)	Consolidated (perf-build-singleton-shared-worker-pool)	Delta / Speedup
Active Worker Threads	24 threads	8 threads	-66.7% threads (-16 threads)
E2E Build Duration (mean)	5,267.1 ms	5,651.3 ms	+7.3% (+384.2 ms)
E2E Build Duration (min / max)	5,187.5 ms / 5,351.7 ms	5,595.6 ms / 5,737.8 ms	+408.1 ms / +386.1 ms
P95 Build Latency	5,351.7 ms	5,737.8 ms	+7.2% (+386.1 ms)
Process RSS Delta	+2,215.3 MB	+2,124.3 MB	-4.1% (-91.0 MB saved)
Final Process RSS	2,296.2 MB	2,204.7 MB	-4.0% (-91.5 MB saved)
Kernel System CPU	3,087.4 ms	3,000.0 ms	-2.8% (1.03x less kernel CPU)
Total CPU (User + Kernel)	19,968.8 ms	17,906.2 ms	-10.3% (-2,062.6 ms CPU saved)

Note on Concurrency Bounds: On high-core machines, baseline's 24 unthrottled concurrent threads across 3 independent pools allow concurrent execution of different compiler phases, whereas the consolidated 8-thread singleton enforces strict concurrency bounds, trading ~380 ms wall-clock time for -2.06s lower total CPU work and lower peak memory. This is particularly important for lower-end machines and resource-constrained CI/container environments to avoid severe CPU starvation, thread thrashing, and out-of-memory crashes.

[alan-agius4]

/gemini review

[gemini-code-assist]

Code Review

This pull request consolidates multiple worker pools into a single shared singleton worker pool that routes JavaScript transformation, Sass rendering, and i18n inlining tasks through a central router. While this consolidation improves resource management, a critical performance bug was identified in the i18n inliner worker: using WeakMaps keyed by Blob objects passed across the worker boundary results in a 0% cache hit rate, as structured cloning creates new Blob instances on every task, bypassing the cache entirely.

[gemini-code-assist]

Code Review

This pull request introduces a shared build worker pool (getSharedBuildWorkerPool) and a central router (shared-worker-router.ts) to consolidate JS transformation, Sass rendering, and i18n inlining tasks into a single worker pool, optimizing resource usage. It also implements bounded in-memory caches in the i18n inliner worker to prevent unbounded memory growth. The review feedback suggests two improvement opportunities: utilizing the new partitionDiagnostics helper in i18n-inliner.ts to reduce duplication, and simplifying the string escaping logic in i18n-inliner-worker.ts for better readability.