The new decompression work in #15667 is too large to review and merge as a single PR. This issue tracks splitting that work into smaller, independently reviewable PRs.

Checklist

• Introduce the core Decompressor API, defensive contract wrapper, input-buffering helper, and one compact implementation (FastLzFrameDecompressor) with shared contract tests: Codec-compression: Add decompressor API #16745.
• Add the generic backpressure decompression handler infrastructure (BackpressureGauge, AbstractBackpressureDecompressionHandler, BackpressureDecompressionHandler) and focused backpressure/read-complete tests.
• Add zlib support (ZlibDecompressor, JdkZlibDecompressor, JZlibDecompressor) and ZlibCodecFactory builder wiring.
• Add remaining per-format decompressor implementations in small PRs: Brotli, Bzip2, LZ4, LZF, Snappy, and Zstd.
• Add HTTP/1.1 decompression integration based on the new API, including native-image reflection configuration and HTTP content tests.
• Add HTTP/2 decompression integration based on the new API, with explicit flow-control tests for padded DATA frames.
• Deprecate the legacy channel-based decompression decoders and document migration paths once replacements are merged and tested.

Until this checklist is complete, the new decompression APIs should be treated as unstable and in progress.