Vary Accumulator Middleware

Accumulates Vary tokens from downstream components (e.g., Accept-Encoding, Accept-Language) and deduplicates them.

Why it matters

Correct Vary headers prevent cache poisoning and ensure CDN/proxy keys are accurate.

Placement (post-global)

postGlobal: [
  \Infocyph\Webrick\Middleware\CompressionMiddleware::class,
  \Infocyph\Webrick\Middleware\VaryAccumulatorMiddleware::class,
  // ...
]