feat(setagg)!: ASAPv1 payloads for SetAggregator and DeltaResult; drop the portable format

[GordonYuanyc]

Part of the ASAPv1-only series: one PR per group, each off main. SetAggregator (0x08 0x00) and DeltaResult (0x09 0x00) only had the portable msgpack format and their ASAPv1 payloads were "TBD". This PR designs them (spec §3.21, §3.22), moves both types onto ASAPv1, and removes the portable format.

Draft for a decision on the payload design below.

Design (spec §3.21 / §3.22)

1. Metadata is {metadata_version: 1} only: no hash-spec group (nothing hashed reaches the wire) and no key_type (the kind_id fixes the element type as str, as with Coco).
2. Payloads: SetAggregator [values], DeltaResult [added, removed]. Empty: [[]] / [[], []].
3. Canonical order: every array strictly ascending in UTF-8 byte order (code point order, not UTF-16). The encoder emits exactly one encoding per set; decode rejects out-of-order or duplicate members rather than re-sorting (as KMV and UniformSampling do).
4. Members are str and valid UTF-8; bin is rejected.
5. DeltaResult's added and removed must be disjoint, enforced on encode and decode.
6. Two kind_ids (from Go's registry), rather than DeltaResult as a variant under SetAggregator's family.

Code

• Types now live in sketches::set_aggregator with a wire.rs (crate-root asap_sketchlib::{SetAggregator, DeltaResult} still resolve). In-memory API unchanged; new serialize_to_bytes / deserialize_from_bytes.
• Removed: message_pack_format::portable::{set_aggregator, delta_set_aggregator}, their MessagePackCodec impls, and DeltaResult's serde derives (the serde form was the removed wire format).
• Goldens (pushed to sketchlib-golden-bytes; submodule bumped): set_aggregator_strings (empty string, proper-prefix chain, 31/32-byte fixstr/str8 boundary, 2/3/4-byte UTF-8), set_aggregator_empty, delta_result_strings, delta_result_empty. Hand-decoded by the reviewer; checked in both directions.

Decisions for you (reviewer recommended keeping each as is)

• metadata without key_type; reject vs canonicalize out-of-order input; enforce disjointness; drop DeltaResult's serde derives (public API break); two kind_ids; module location under sketches/.

Downstream

ASAPQuery's delta_set_aggregator_accumulator.rs calls DeltaResult::to_msgpack(); it must switch to serialize_to_bytes(), its sink bytes change format, and a DeltaResult with a key in both sets now fails to encode. sketchlib-go has no implementation yet.

Verification (rustc 1.99)

cargo fmt --check; clippy -D warnings for all four CI feature sets; RUSTDOCFLAGS="-D warnings" cargo doc; gen-proto drift clean; --lib -- set_aggregator, asapv1_golden, pbt -- set_aggregator::, e2e -- set_aggregator, msgpack_compat. Wire code mutation-checked. Implemented and reviewed by separate agents; review findings are addressed in the second commit.

🤖 Generated with Claude Code

[GordonYuanyc]

Outdated. ASAPv1 encodings and goldens landed in #232 and #235 against the current spec; removing the legacy formats is redone on current main in #206 and #207.