fix(examples): redesign curve-bevel-arc as a horseshoe magnet with field-line filings (#277)

The old hero was one plain rose tube lying on the floor: programmer art
that said nothing about why a capped, beveled Bezier curve matters.

The checked curve is now staged as a round-bar horseshoe magnet: red
enamel with ground-steel pole ends (one material keyed on object-space Y,
so it stays a single curve datablock). Its two filled caps - the
use_fill_caps witness - are the pole faces, turned to the camera, where an
uncapped build would show hollow pipe ends. Paper clips are beveled Bezier
curves too (FREE handles, straight legs plus quarter-circle bends) lying
along the field lines, and iron filings trace those lines as exact
circular arcs between the poles.

The check is unchanged (same constants, same exits); only the object
transform changes, after the check. The render path gains the
asset-quality gate (exit 11). gallery_asset_quality now measures curve
objects as parts (edge90 on the evaluated tessellation, freed with
to_mesh_clear), and the asset-sheet panel keeps curve objects, so a
curve-built asset is measured and shown instead of silently skipped. No
existing caller passes a curve object; prop-origin-transform's floors are
identical before and after.

Signed-off-by: TMHSDigital <154358121+TMHSDigital@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: TMHSDigital

README.md

@@ -408,16 +408,17 @@ lifting and flaring the rim — authored through `shape_key_add` / `key_blocks`
 </tr>
 <tr>
 <td width="46%" valign="middle">
-<a href="examples/curve-bevel-arc/"><img src="examples/curve-bevel-arc/preview.webp" alt="Curve bevel arc: a rose beveled Bezier semicircle tube resting on a dark studio floor, both filled end caps facing the camera" /></a>
+<a href="examples/curve-bevel-arc/"><img src="examples/curve-bevel-arc/preview.webp" alt="Curve bevel arc: a red horseshoe magnet built from one beveled Bezier curve, its filled end caps turned to the camera as steel pole faces, iron filings arcing between the poles and Bezier-wire paper clips clinging to them" /></a>
 </td>
 <td valign="middle">
 
 ### [curve-bevel-arc](examples/curve-bevel-arc/)
 
 A beveled Bezier semicircle authored on `bpy.types.Curve` — `splines.new('BEZIER')`,
 `bezier_points`, `bevel_depth`, `use_fill_caps` — so the curve renders as a solid tube
-without a prior mesh conversion. Asserts eight points, `bevel_depth == 0.15`, and
-evaluated topology 1044 verts / 1028 faces.
+without a prior mesh conversion — staged as a horseshoe magnet whose capped ends
+are the pole faces. Asserts eight points, `bevel_depth == 0.15`, and evaluated
+topology 1044 verts / 1028 faces.
 
 </td>
 </tr>

docs/gallery/asset-sheets/curve-bevel-arc.webp

@@ -475,7 +475,7 @@ <h2><a href="shape-key-blend/">shape-key-blend</a></h2>
       </article>
       <article class="card" data-tags="curves bevel">
         <a class="card-media" href="curve-bevel-arc/" tabindex="-1" aria-hidden="true">
-          <img src="assets/curve-bevel-arc-hero.webp" alt="A magenta beveled curve tube lying in a semicircle on a dark floor, both filled end caps facing the camera." loading="lazy" decoding="async" />
+          <img src="assets/curve-bevel-arc-hero.webp" alt="A red horseshoe magnet made of one beveled Bezier curve on a dark floor, its filled end caps facing the camera as steel pole faces, iron filings arcing between them." loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="curve-bevel-arc/">curve-bevel-arc</a></h2>

docs/gallery/assets/curve-bevel-arc-hero.webp

@@ -11,11 +11,20 @@ and that the depsgraph-evaluated mesh has the deterministic topology (1044 verts
 1028 faces for these resolution settings) with a Z span that rests on the floor
 (`[0, 2 × bevel]`) and an X span of `2 × radius + 2 × bevel`.
 
-Staging: both ends of the semicircle face −Y, so the still looks from −Y and
-shows both filled caps (`use_fill_caps`, the witness) face-on, with the arc
-sweeping behind them. The old angle showed one cap and the other end edge-on.
-The cap's 12-sided outline is the pinned tessellation (`bevel_resolution` 4,
-locked by the 1044-vertex gate), not a presentation choice.
+Staging: the checked curve is presented as what a capped, beveled Bezier
+semicircle is in the world — a round-bar horseshoe magnet lying on the floor,
+open end to the camera. The two filled caps (`use_fill_caps`, the witness) are
+its ground-steel pole faces, turned face-on; an uncapped build would show two
+hollow pipe ends exactly there. The red enamel / bare-steel split is one
+material keyed on object-space Y, so the magnet stays a single curve
+datablock. The paper clips are beveled Bezier curves too (explicit `FREE`
+handles: straight legs plus quarter-circle bends), each lying along the field
+line that leaves its pole; the iron filings trace those lines — for two
+opposite line poles they are exact circular arcs through both pole faces. The
+cap's 12-sided outline is the pinned tessellation (`bevel_resolution` 4,
+locked by the 1044-vertex gate), not a presentation choice. The render path
+rotates the object only; the check reads object-space evaluated geometry and
+runs before any staging.
 
 ## Run
 
@@ -49,7 +58,7 @@ against it. `10` is also the shared framing helper.
 | 8 | Tube does not rest on the floor |
 | 9 | Tube height ≠ 2 × bevel |
 | 10 | X span off closed form; also gallery framing violation |
-| 11 | `--output` produced no file |
+| 11 | `--output` produced no file; also asset-quality floor violation (`gallery_asset_quality`) |
 
 The `blender-smoke` workflow runs the check on Blender 5.2 LTS and 4.5 LTS
 (5.1 on the weekly cron, the `needs-5.1` PR label, or manual dispatch).