v0.2.0

Performance

• LZ4 hot-path allocation reduced by ~99.997%. Compression::Lz4's encode
  path now amortizes its internal hash table across calls via lz4_flex 0.13's
  new compress_into_with_table API and a per-thread CompressTable. The
  per-record 8 KiB hash-table allocation that dominated heap traffic on
  LZ4-heavy workloads (~1.2 GiB cumulative across 300 K records on lz4_flex
  0.11) is now amortized to a single 8 KiB allocation per encoder thread for
  the process lifetime. Measured: 24.9 KiB total across 100 000 LZ4 sends
  in the kafko-bench lz4_sequential scenario (0.10% of total process
  allocation, down from 93%). LZ4 sequential throughput now tracks no-codec
  sequential throughput within 3% (164 K vs 160 K rec/s on the same path).

Added

• Cargo features for compression codecs. Two new opt-in features —
  compression-lz4 and compression-zstd, plus the convenience
  compression-all — make lz4_flex and zstd optional dependencies. A
  default cargo add kafko no longer pulls either codec into the dep tree.
  Compression::Lz4 and Compression::Zstd remain visible in the public API
  regardless of feature flags so on-disk records written by another build are
  detectable and produce a friendly KafkoError::CompressionUnavailable
  rather than mis-decoding.
• KafkoError::CompressionUnavailable(Compression) — error variant returned
  when encoding or decoding a record under a codec whose Cargo feature is not
  enabled. Display message names the missing feature.
• Compression::is_available() -> bool — runtime feature detection for
  callers that want to fall back gracefully between codecs.
• kafko-bench lz4_sequential scenario — mirrors the sequential scenario
  under Compression::Lz4 so the hotpath alloc table can attribute
  compression::compress heap traffic to the LZ4 path specifically. Gated
  behind the compression-lz4 feature.
• [package.metadata.docs.rs] — docs.rs builds with all-features so both
  codec variants are documented in full on the rendered crate page.

Changed (breaking)

• Record::encode_with signature. Previously -> usize; now
  -> Result<usize>. The error case is KafkoError::CompressionUnavailable,
  returned when encoding under a codec whose feature is not enabled. Callers
  using Producer::send / Producer::send_batch are unaffected — the
  Producer API was already Result-returning and propagates the new error
  naturally. Callers using Record::encode_with directly must add ? or
  .unwrap(). Record::encode() (the Compression::None convenience) is
  unchanged.
• Default Cargo features. Previously lz4_flex and zstd were
  unconditional dependencies; now both are gated behind opt-in features. A
  cargo update kafko from 0.1.1 to 0.2.0 for a downstream pinned at
  ^0.1 will silently drop LZ4/Zstd support until features are added.
  To preserve v0.1.1 behaviour, change the dependency to:

  kafko = { version = "0.2", features = ["compression-all"] }

Internal

• lz4_flex bumped from 0.11 to 0.13. The 0.11 line is in maintenance mode;
  0.13 ships the same security fixes as 0.11.6 plus the
  compress_into_with_table API that enables the per-thread hash-table reuse
  win above. Wire format unchanged; existing on-disk segments read back
  identically.
• New LZ4_TABLE: RefCell<lz4_flex::block::CompressTable> thread-local in
  crates/kafko/src/compression.rs alongside the existing
  ZSTD_COMPRESSOR/ZSTD_DECOMPRESSOR thread-locals.