3D effects: resolve a profile only when its contours meet

The boolean that merges crossing contours cost about as much as the rest
of a plain extrusion, and it ran on every profile. Most art has no
contours that meet, so the profile is now sampled first (its point limit
checked there, before any boolean) and resolved only when two edges
cross, touch, run along each other or fold back, in one contour or
across two. Edges are swept by their left ends, within a pair budget past
which the boolean decides. Touching counts: squares sharing an edge
inflate as one puff, not two with a seam.

On a release build, Extrude of 120 separate contours takes 0.31 ms
instead of 4.18 ms; profiles that do cross cost what they did.

Tests: the meeting cases, squares sharing an edge, the fallback for a
profile the boolean refuses, Inflate's extent and area for the crossing
k, and the coincident circles' area. The hairline test now holds a
crossing pair so that its profile still goes through the boolean.

Docs: the merge is described once for all three effects, linking to a new
Limits section in the pathops README instead of repeating its limits,
and the point limit notes that a merged outline can have more points.

docs/three-d.md

@@ -17,6 +17,11 @@ Preview changes are temporary until OK; Cancel restores the document; OK is one
 3D effect: edit its options in the Appearance panel or the 3D and Materials panel, or remove it before applying
 another.
 
+Each solid follows its shape as it is filled. Separate and nested contours are built as drawn. Contours that cross,
+touch or run along each other or themselves, as type often draws a glyph, are first merged into one outline by
+[`vectorcraft-pathops`](../crates/pathops/README.md), keeping contours however narrow. All three effects then share
+its [limits](../crates/pathops/README.md#limits): a shape it refuses is built from its contours as drawn, where it can be.
+
 ## 3D and Materials panel
 
 **Window › 3D and Materials** opens a panel that edits the 3D effect of the selection without a dialog, as the
@@ -62,8 +67,7 @@ object is where the art was.
 | Bevel Inside | The bevel carved into the shape (the front face shrinks) instead of added around it (the walls stand outside the art). |
 | Bevel both sides | The back is bevelled too. |
 
-Holes stay holes, with walls of their own. Contours that cross or overlap, as type often draws a glyph, are merged
-first, so the solid follows the shape as it is filled. Bevels move each corner along its bisector (mitres are limited to four
+Holes stay holes, with walls of their own. Bevels move each corner along its bisector (mitres are limited to four
 times the width), so a bevel wider than a narrow part of the shape folds over itself.
 
 ## Inflate
@@ -229,7 +233,9 @@ out, perspective). No Adobe software, assets, presets or bevel shapes were used.
   effect per object.
 - Curves are followed within 1/2000 of the shape's size (at least 0.05 pt), so a small curve takes a few points
   and a large one up to 32. Extrude & Bevel and Inflate take up to 2,048 outline points (a stroke's outline is
-  counted on its own), Rotate (which only turns the outline) 65,536.
+  counted on its own), Rotate (which only turns the outline) 65,536. The limit is counted on the shape as drawn and,
+  when its contours meet, again on the merged outline, which can have more points: bars crossing in a grid trace
+  every hole between them.
 - **3D (Classic)** (the track cube, surface types, blend steps, map art), Turntable and 3D export are separate,
   unbuilt items.
 
@@ -239,6 +245,7 @@ Release measurements and a repeatable CLI scene are in [3D lighting performance]
 
 | Date | Change |
 |---|---|
+| 2026-11-08 | Contours that cross, touch or overlap are merged by vectorcraft-pathops before Extrude & Bevel, Inflate and Rotate build a solid, sharing its limits; others are built as drawn. |
 | 2026-11-06 | Extrude & Bevel, Inflate and Rotate apply to groups and layers: every path, compound path and type in them turns about one shared axis (#4506). |
 | 2026-10-21 | Four original lighting presets, shared by all four 3D effects and commands, with effective-setting recognition and existing preview/history behavior. |
 | 2026-10-17 | Smooth colored Inflate lighting and surface batching; legacy white-light appearance and the 0.05 seam minimum preserved; shared light Color and multiple lights remain vector output. |