docs(adr-0012): re-affirm portable zstd-encode deficit via RM-309 survey [RM-309]#72
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…vey [RM-309] Survey the pure-Rust streaming zstd encoder landscape for DEV-123. Latest ruzstd (0.8.3, pinned) exposes only compress_to_vec (one-shot) and the pull-based FrameCompressor (set_source(Read)/set_drain(Write)/blocking compress()); neither is push-drivable for the engine's bounded ZIP-member write loop without whole-member buffering or a thread, both barred by core invariants. structured-zstd (fork) has the same architecture; zstd/zstd-safe are C/zstd-sys (native-only). No suitable portable crate exists. Record the survey and re-affirmed resolution path in the ADR-0012 deficit ledger, sharpen the deficit row's "why" (pull vs push) and document the concrete adoption seam (provider.rs map_zip_method arm + zip_stream.rs zstd_step, ADR-0011 interop evidence before any support-matrix flip). No src/ change; native-codecs-only method-93 write stays a tracked interim. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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July 23, 2026 21:38
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Documents the RM-309 (DEV-123) survey of the portable pure-Rust streaming zstd encoder landscape. Docs-only — no
src/change, no support-matrix cell flipped.Survey verdict: deficit re-affirmed
No suitable portable, C/FFI-free,
forbid(unsafe)-compatible streaming zstd encoder exists:compress_to_vec(one-shot) andFrameCompressor(pull-basedset_source(Read)→set_drain(Write), one blockingcompress()to EOF). Neither can be driven by the engine's push-based, bounded ZIP-member write loop without inverting control (whole-member buffering or a thread) — which would break the core bounded-memory guarantee.zstd-syswrappers, disqualified fromportable-codecs.So the
native-codecs-only ZIP method-93 write stays a legitimate tracked interim per ADR-0012. ThePortable streaming zstd encodeledger row is sharpened (pull-vs-push distinction,FrameCompressorcited) and now records the concrete adoption seam for a future crate. No core invariant changes.🤖 Generated with Claude Code