mesh: a screw hole's ring takes in the fillet of its rounded corner; frames centred on the hole (#402)

The projection layout gave every fillet a blend layer along the sides it runs between, so a
screw hole close to a rounded corner sat inside the layer and the plan fell back to frame cuts
and swept cells, which fan into the hole. A corner fillet that lies inside the square from the
hole to the two sides is now taken in by the hole's O-grid ring: the frame reaches both sides,
its outer corner projects onto the middle of the fillet, and no layer is needed. An O-grid's
frame is centred on its hole (a near side is the frame, the far side as far), and the plan
reports the layout's frames and drops the frame-cut notes when it does not cut.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

skills/fieldcraft-meshing/SKILL.md

@@ -28,8 +28,9 @@ not guessed. Read it before you plan anything:
    `mesh.plan.apply {"plan": "Plan-<body>"}`. When the plan has rings or blends and the body
    fits, its `mesher` is `project`: one block topology over the whole body (a grid on the
    body's planar faces, an O-grid square-inside-square round every circle, concentric ones
-   nested: a boss and its hole; a blend layer along fillets, chamfers and shell walls at their
-   stored depth) projected and smoothed — no partitions, one conforming mesh, one division
+   nested: a boss and its hole, frames centred on the hole; a screw hole in a rounded corner
+   takes the corner's fillet into its ring; a blend layer along fillets, chamfers and shell walls
+   at their stored depth) projected and smoothed — no partitions, one conforming mesh, one division
    count per sheet of blocks. Read `layout` and `blend_layers`; the plan's `notes` say why a
    body did not fit (a plane at an angle, a curved face that is not a ring or a blend, two
    circles in one frame), and then the frame cuts and swept cells are used instead (`pending`