CTS Building Builder Pro v1.0.20

CONFIRMED CONNECTED-WALL ROOT CAUSE
- Corrected Boolean operand order to cutter.subtract(wall).
- SketchUp's own test_subtract vendor test confirms that the receiver is the
  cutter and the argument is the retained wall.
- Native planar Push/Pull was not affected and is unchanged.

CONNECTED PATH CORRECTIONS
- A mixed selection of a bent chain and separate straight guides no longer
  abandons the continuous cutter.
- Keeps curved-path segments down to the same 0.025 mm chain tolerance.
- Selected Portion keeps the prepared path endpoints exactly; no hidden extra
  extension is added after the explicit Wall Edges/Extra Length settings.
- Works in a unit-scale world frame for scaled or mirrored nested parents.
- Equal-width grooves use a simple four-point rectangular profile.
- Recess depth no longer includes an unwanted extra 1 mm.
- Selected loose guide wires inside a wall are removed within the same undo
  operation before checking the host solid. Unrelated wires are untouched.
- A failed sweep no longer silently falls back to the old corner engine.

WALL RETENTION SAFEGUARDS
- Requires a valid closed wall result after every cut.
- Checks that volume removed cannot exceed the complete cutter volume.
- Checks that the result stays within the original wall bounds.
- Checks that sampled untouched wall points still exist on the result shell.
- Reuses each replacement wall for subsequent grooves and restores metadata.
- Native failures propagate to the existing error report and abort the single
  operation instead of committing a partial or missing wall.

RESEARCH BASIS
https://ruby.sketchup.com/Sketchup/Group.html#subtract-instance_method
https://github.com/SketchUp/sketchup-developer-tools/blob/master/src/sketchup-developer-tools/testup/tests/ruby_classes/TC_ComponentInstance.rb

VALIDATION LIMIT
Automated Ruby syntax, geometry-math and strict API-contract regressions are
run outside SketchUp. They do not execute SketchUp's native Follow Me/Boolean
geometry kernel. The user's connected and curved wall model must be checked
in SketchUp after installation and restart.

All previous tools, UI layout, presets and properties are retained.
