3802.feature.md

Add support for rectilinear (variable-sized) chunk grids. This feature is experimental and must be explicitly enabled via zarr.config.set({'array.rectilinear_chunks': True}).

Rectilinear chunks can be used through:

• Creating arrays: Pass nested sequences (e.g., [[10, 20, 30], [50, 50]]) to chunks in zarr.create_array, zarr.from_array, zarr.zeros, zarr.ones, zarr.full, zarr.open, and related functions, or to chunk_shape in zarr.create.
• Opening existing arrays: Arrays stored with the rectilinear chunk grid are read transparently via zarr.open and zarr.open_array.
• Rectilinear sharding: Shard boundaries can be rectilinear while inner chunks remain regular.

Breaking change: The validate method on BaseCodec and CodecPipeline now receives a ChunkGridMetadata instance instead of a ChunkGrid instance for the chunk_grid parameter. Third-party codecs that override validate and inspect the chunk grid will need to update their type annotations. No known downstream packages were using this parameter.