Fix single-layer overlap carving

[0hmX]

Summary

• bug: single-layer carve remove other layer too
• fix: carve only shared layer; keep other layer in overlap core
• rebuild shared multilayer rects; split helper fns one-per-file

Example

Before:

• A rect (0..10,0..10) layers [0,1]
• B rect (4..6,4..6) layers [0]
• overlap core removed for layer 1 too (wrong)
  After:
• overlap core keeps layer [1]
• only layer [0] removed in core
• shared rects rebuilt into multilayer blocks

[vercel]

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Project	Deployment	Actions	Updated (UTC)
rectdiff	Ready	Preview, Comment	Apr 15, 2026 3:14pm