feat: Support for mask-mode

[hex2f]

Adds support for the mask-mode property, which controls whether a mask-image is interpreted as an alpha mask or a luminescence mask.

Implementation

• parseMask reads mask-mode (and the -webkit- prefixed variant) and stores it on the parsed mask, defaulting to match-source.
• buildMaskImage emits mask-type="alpha" or mask-type="luminance" on the SVG mask element when explicitly set. For match-source no attribute is emitted, falling back to the default (luminance), preserving
  the existing rendering behavior.

Following the existing convention in parseMask (where position, size, repeat, origin, and clip apply as a single value to all layers), maskMode also applies once per element rather than per-layer. This maps cleanly onto SVGs per- mask-type attribute.

Testing

I have added a test which checks that mask-type= is properly applied to the SVG. There should probably be a pixel snapshot test added but I couldn't figure out how to do that, will add if required. All existing tests pass.

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Project	Deployment	Actions	Updated (UTC)
satori-playground	Canceled	Open in v0	May 2, 2026 11:15pm