[alan-agius4]

Summary

• When TypeScript's BuilderProgram.emitNextAffectedFile emits .d.ts-only (emitOnly = Dts) for an affected transitive importer, TypeScript skips transformers.before and runs transformers.afterDeclarations. ensurePreDeclarationTransformers runs before transformers inside afterDeclarations to populate Angular's dtsTransforms, and caches the transformed ts.SourceFile in preTransformedSourceFiles only for those .d.ts-first files (deleting the entry immediately when consumed by a subsequent .js emit).
• For normal .js-first / combined .js + .d.ts emits, tracks seenSourceFiles via a Set<ts.SourceFile> without retaining transformed SourceFile ASTs in memory across the emit loop.

Benchmark Results

Metric	main	Branch	Delta
Runs (ms)	11814, 11582, 11874, 11927, 12264	11584, 11679, 11758, 11764, 11807
Median (ms)	11874 ms	11758 ms	-0.98% (-116 ms)
Mean (ms)	11892 ms	11718 ms	-1.46% (-174 ms)
Min (ms)	11582 ms	11584 ms	+0.02% (+2 ms)

[gemini-code-assist]

Code Review

This pull request exports and refactors the ensurePreDeclarationTransformers function in aot-compilation.ts to properly cache and reuse pre-transformed source files. The implementation now combines all before-transformers into a single transformer and utilizes a map to cache the transformed ASTs during the declaration emit phase, preventing redundant executions when subsequently emitting JavaScript. Comprehensive unit tests have also been added in angular-compilation_spec.ts to verify this behavior. There are no review comments, so I have no feedback to provide.