feat(writer): cascade zigzag like Rust's ZigZagScheme (issue #410) - #436
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Parity with the reference compressor: ZigZag overrides encodeCascade and hands its unsigned output to the compressor as an open child, with Rust's descendant exclusions (Dict, RunEnd, Sparse; plus itself), and is not applicable without a negative value. It is now also a cascade candidate, as in Rust; before, it was never offered to the cascade at all. Output is byte-identical on every size comparison: FoR competes for the same columns and never needs more bits (bits(max - min) <= bits(2 * max|v|)), so it wins or ties. Rust's dict-codes ancestor rule holds by construction: codes are unsigned and ZigZag accepts signed only. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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Part of #410, Rust-parity port number 2 after RunEnd (#435).
ZigZagEncodingEncoder.encodeCascade: the zigzag output (the unsigned counterpart:I32→U32, which is what our decoder already reads) becomes an open child. It is not applicable without a negative value, matching Rust'smin_is_negativeskip. The negative check is a read-only scan before anything is allocated, since ourArrayStatscarries no minimum.ZigZagScheme: Dict, RunEnd, Sparse (a bijection preserves cardinality, runs and dominance, so they would lose again), plus ZigZag itself.buildCascadeCodecsbefore, so the cascade never tried it.Size: byte-identical on every comparison (FileSizeComparison 1,161,559, GlobalDict 2,466,808, …) and on a mixed-sign probe. FoR competes for the same columns and never needs more bits:
bits(max − min) ≤ bits(2·max|v|), with a tie when the data is symmetric around zero. This PR is for parity, not size.Tests:
ZigZagEncodingEncoderTest.Cascade(I8 zigzag values including the extremes, the child dtype, exclusions, bounds from the signed values, the no-negatives skip). Green: 1,925 writer, 1,592 reader and 367 integration tests, including every vortex-jni interop suite.No CHANGELOG entry: output is unchanged, so nothing is user-visible.
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