fix: scan misaligned per-column chunk grids (#221)

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Per-zone stats from current Rust writers (`vortex.zoned`, vortex-jni 0.76.0) decode again. The 0.76 zoned layout replaced the legacy `vortex.stats` bit-set metadata with an aggregate-function spec list and dropped the per-stat truncation flags; the reader now reconstructs the stats table from that spec list (min/max/sum/null_count), so `columnZoneStats` and aggregate push-down work against those files instead of throwing `ClassCastException`. ([#197](https://github.com/dfa1/vortex-java/pull/197))
+- Scans of files whose columns use different chunk grids no longer fail with `mixed per-column chunking beyond 1-vs-N is not supported`. The scan planner now splits at the merged boundary grid — the sorted union of every column's chunk boundaries, matching the Rust reference — and decodes each column's covering chunk once, slicing it zero-copy to each window. This handles both nested grids (Raincloud `emotions-dataset-for-nlp`, where `label`'s coarse chunks nest inside `text`'s finer grid) and disjoint grids (`uci-beijing-multi-site-air-quality`, where numeric and `station` boundaries do not nest). Aligned N-vs-N and 1-vs-N scans keep their existing slice-free fast path. ([#221](https://github.com/dfa1/vortex-java/issues/221))
 - CSV export renders nested struct columns as JSON object cells (`{"field":value,...}`, strings JSON-escaped, null fields as JSON `null`, nested structs recursed) instead of throwing `unsupported array type: StructArray`. ([#217](https://github.com/dfa1/vortex-java/issues/217))
 - Scanning a struct whose columns include a nested struct no longer fails chunk planning. A nested `vortex.struct` layout column (e.g. Raincloud `countries-of-the-world`'s `data` column) is now treated as a single full-range chunk source and decoded through the layout registry's new struct decoder into a `StructArray`, matching the Rust reference (a nested struct spans its parent's row range, not an independent chunking). `schema`/`count`/`inspect` already worked; plain scans and `select` of sibling columns now work too. CSV export of the struct column itself remains unsupported (a separate rendering limitation). ([#207](https://github.com/dfa1/vortex-java/issues/207))
 - CSV export renders unsigned integer columns (U8–U64) with their unsigned values — high-half values previously printed as two's-complement negatives (uci-wine `magnesium` U8 132 exported as -124), silent corruption found by the Raincloud conformance suite. ([#208](https://github.com/dfa1/vortex-java/issues/208))

docs/compatibility.md

@@ -62,9 +62,11 @@ Per-slug status lives in `integration/src/test/resources/raincloud/expected-stat
 (`ok` must pass; `gap:<issue>` must still fail, so a fix flips the entry in the same change;
 `untriaged` runs and reports without failing the build). A scheduled workflow
 (`raincloud-conformance.yml`) hydrates a size-capped subset weekly. Current triage —
-28 `ok`, 2 known gaps (both misaligned per-column chunk grids,
-[#221](https://github.com/dfa1/vortex-java/issues/221)); 217 slugs untriaged. Fixed so far
-by this suite: lazy dict U8/U16 values ([#206](https://github.com/dfa1/vortex-java/issues/206)),
+30 `ok`, 0 known gaps; 217 slugs untriaged. Fixed so far
+by this suite: misaligned per-column chunk grids
+([#221](https://github.com/dfa1/vortex-java/issues/221) — scan now splits at the merged boundary
+grid, slicing each column's covering chunk per window), lazy dict U8/U16 values
+([#206](https://github.com/dfa1/vortex-java/issues/206)),
 nested struct columns in scan ([#207](https://github.com/dfa1/vortex-java/issues/207)),
 unsigned integers rendered signed ([#208](https://github.com/dfa1/vortex-java/issues/208) /
 [#216](https://github.com/dfa1/vortex-java/issues/216) — silent corruption, incl. wrong filter

integration/src/test/resources/raincloud/expected-status.csv

@@ -91,7 +91,7 @@ diabetes-health-indicators-dataset,untriaged
 disease-symptom-description-dataset,untriaged
 docmatix-zero-shot,untriaged
 electric-motor-temperature,untriaged
-emotions-dataset-for-nlp,gap:221
+emotions-dataset-for-nlp,ok
 fhv_tripdata_2025,untriaged
 fhvhv_tripdata_2025,untriaged
 finemath-4plus,untriaged
@@ -193,7 +193,7 @@ uci-air-quality,ok
 uci-auto-mpg,ok
 uci-automobile,untriaged
 uci-bank-marketing,ok
-uci-beijing-multi-site-air-quality,gap:221
+uci-beijing-multi-site-air-quality,ok
 uci-bike-sharing-dataset,ok
 uci-breast-cancer,untriaged
 uci-breast-cancer-wisconsin-diagnostic,untriaged