Hold the type of a soft mask in the path columns #618

Context

DESIGN.md section 10. #606 added Paths, whose soft_mask column indexes Paths.soft_masks, the distinct soft masks of the page. hayro 0.9 (#609) reduced a soft mask to its type, so that tuple now holds at most the two values of SoftMaskType, in the order in which the page first paints them. A reader has to go through it to read what the other enum columns (fill_rule, stroke_cap, stroke_join, blend_mode) state directly.

No release holds Paths yet, so this changes no released API. The owner chose this change in the working session of 2026-11-04, after #606's layout had been agreed.

Goal

soft_mask holds the position of the soft mask's type in SoftMaskType, or -1 where the path has none, and Paths.soft_masks no longer exists.

Scope

In:

• The column as an int8, which Arrow imports as int8, null where it is -1.
• Removing Paths.soft_masks and what only it needs in the binding.
• The tests, the API reference, and the column sizes in evidence/path-columns/.

Out:

• The rest of the layout.
• Removing SoftMask.xref, which Move to hayro 0.9 with LaurenzV/hayro#1734 patched in, and read streams that name a file #609 deprecated.

Paths

crates/pyropdf-python/src/buffers.rs, python/pyropdf/_content.py, python/pyropdf/_core.pyi, tests/test_path_columns.py, docs/en/api/text-and-content.md, and evidence/path-columns/.

Acceptance

• On every corpus page, and on a page that paints a luminosity mask before an alpha mask, soft_mask holds the position of Path.soft_mask.subtype in SoftMaskType, or -1
• NumPy reads the column as int8, and Arrow imports it as int8, null where it is -1
• Paths has no soft_masks, and evidence/path-columns/ shows the new size of the columns

Notes

The row view builds each SoftMask with _soft_mask, as Content does, so the records still equal Content.paths.