[wieslawsoltes]

Problem

Localized scene damage used raw command boxes. Descendant changes inside a retained foreground blur could therefore leave stale pixels in the blur fringe during partial redraw.

Change

• derive a bounded per-command blur extent from the active kind 30/31 group stack
• expand old and new changed-command bounds by cumulative 3 × sigma
• cover changed blur groups and descendants, including nested/repeated blurs
• preserve the existing two-pixel antialias pad and 40% full-damage fallback
• add a native mutation regression that requires localized expanded damage

Validation

Tests and builds were deliberately not executed under the current implementation-throughput directive. Native/backend pixels, partial-redraw behavior, performance, memory, lifecycle, package, and CI gates remain required before release promotion and are recorded in #491/#256/#235.

Closes #491