Support flat mappings for automatic region holes

[Irev-Dev]

The engine will returns a flat region mapping that includes segments generated for automatically detected holes. KCL was creating artifacts for those segments, but the region path did not retain them and point-and-click selection could not follow an original sketch segment through to its swept faces. As a result, selecting an edge around an automatic hole could fail to produce the face references needed by operations such as chamfer and fillet.

This replaces the grouped-loop approach from #12414 and is intended to work with KittyCAD/engine#4786.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
modeling-app	Ready	Preview, Comment	Jul 16, 2026 4:16am

[codspeed-hq]

Merging this PR will not alter performance

✅ 126 untouched benchmarks
⏩ 151 skipped benchmarks¹

---

_{Comparing kurt-flat-auto-hole-region-mapping (61049b8) with main (4f69d73)²}

Footnotes

1. 151 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (9a94c85) during the generation of this report, so 4f69d73 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩