Photoshop pads every layer-level tagged block to a multiple of 4 inside the length field; all 567 Photoshop-authored fixtures in the corpora do. The exporter padded regenerated blocks to even only, so a Pattern Fill's PtFl came out 2 bytes short of the boundary for half of all pattern names and left the layer record's extra data unaligned.
The pad is applied where the fill blocks are regenerated, not in the generic loop: preserved blocks must stay byte-identical (psd_structure, roundtrip) and shmd is length-structured (comps_artboards).
Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>
