Switch the payload compression codec to zstd, which benchmarks 3–7×
faster than gzip at an equal-or-better ratio on representative workloads
(compression runs at every step boundary, so the write CPU is a per-step
tax). zstd uses node:zlib (>= 22.15); gzip via the portable
CompressionStream remains the fallback when zstd is unavailable, and
WORKFLOW_COMPRESSION_CODEC=gzip forces it. Reads dispatch on the format
prefix, so 'zstd' and 'gzip' payloads are both always decodable.
zstd is Node-only (Web CompressionStream has no zstd), so the browser
o11y read path registers a WASM-backed decoder (@tootallnate/zstd-wasm)
via a new registerZstdDecoder hook; node:zlib handles Node-side reads
(runtime replay, CLI, server o11y). A new workflow.serialization.codec
span attribute reports which codec applied. gzip and zstd read support
co-ship, so the existing specVersion-5 capability gate is unchanged.
Verified end-to-end: spec-5 runs store zstd-prefixed payloads on disk
and replay/complete correctly; the WASM decoder round-trips node:zlib
zstd output. Benchmarks updated to compare zstd vs gzip.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Pranay Prakash