The decimate tool in the Surface Toolbox produces the same output with or without the “Boundary deletion” checkbox selected. On debugging, it looks like there’s a typo in the parameter name here:
Which should be consistent with the definition here:
Changing the name on line 537 resolves the issue. I can submit a pull request with this change if this looks correct.
Good catch. Yes, please send a pull request (keep
decimationBoundaryDeletion). Thank you!