feat(showcase): add butter-churn (#256)

The butter churn was the first unclaimed standalone showcase candidate.
What an envelope check cannot see on a churn is whether the dasher can
plunge: the body narrows toward the top, so a plunger that clears the
staves at rest can jam a hand's width up the stroke while it still sits
inside the body untouched. The piece reads the inner wall off the
staves and the plunger's reach off the dasher and asserts a 400 mm
stroke floor; --wide-dasher exits 20 at 140 mm while every other budget
and the envelope still pass.

Also asserts every stave on the floor, a three-board bottom, the handle
biting the slats, hoops seated vertex-for-vertex on the staves, the lid
on the stave tops and the handle clearing its hole, each with a
falsifier proven on 4.5.11, 5.1.2 and 5.2.1. The ox-cart tongue entry
moves behind the bookshelf: it was a restock placed ahead of older
candidates, and it needs the yoke as its hitch partner.

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

Author: TMHSDigital

.cursor-plugin/plugin.json

@@ -170,6 +170,7 @@
     "showcase/grain-sacks",
     "showcase/brazier",
     "showcase/apothecary-shelf",
-    "showcase/wooden-yoke"
+    "showcase/wooden-yoke",
+    "showcase/butter-churn"
   ]
 }

CLAUDE.md

@@ -22,7 +22,7 @@ rules/<rule-name>.mdc          - Anti-pattern rules, 9 total
 templates/<template-name>/     - Starter projects, 3 total
 snippets/<snippet-name>.py     - Standalone code patterns, 27 total
 examples/<name>/               - Runnable smoke-gated examples, 59 total (+ gallery.json)
-showcase/<name>/               - Budget-conformance props, 33 pieces (sibling of examples/; see showcase/README.md)
+showcase/<name>/               - Budget-conformance props, 34 pieces (sibling of examples/; see showcase/README.md)
 scripts/build_gallery.py       - Regenerates docs/gallery/ from examples/gallery.json + showcase/gallery.json
 scripts/site/                  - Vendored landing-page build (Jinja2)
 docs/gallery/                  - Committed generated gallery pages + hero renders

README.md

@@ -18,7 +18,7 @@
 </p>
 
 <p align="center">
-  <strong>16 skills</strong> &nbsp;&bull;&nbsp; <strong>9 rules</strong> &nbsp;&bull;&nbsp; <strong>3 templates</strong> &nbsp;&bull;&nbsp; <strong>27 snippets</strong> &nbsp;&bull;&nbsp; <strong>59 examples</strong> &nbsp;&bull;&nbsp; <strong>33 showcase pieces</strong>
+  <strong>16 skills</strong> &nbsp;&bull;&nbsp; <strong>9 rules</strong> &nbsp;&bull;&nbsp; <strong>3 templates</strong> &nbsp;&bull;&nbsp; <strong>27 snippets</strong> &nbsp;&bull;&nbsp; <strong>59 examples</strong> &nbsp;&bull;&nbsp; <strong>34 showcase pieces</strong>
 </p>
 
 <p align="center">
@@ -37,7 +37,7 @@
 
 ## Overview
 
-This repository ships **16 skills, 9 rules, 3 templates, 27 snippets, 59 examples, and 33 showcase pieces** for Blender Python development targeting Blender 5.2 LTS (current stable) with Blender 4.5 LTS fallback support. Blender 5.1 is prior stable.
+This repository ships **16 skills, 9 rules, 3 templates, 27 snippets, 59 examples, and 34 showcase pieces** for Blender Python development targeting Blender 5.2 LTS (current stable) with Blender 4.5 LTS fallback support. Blender 5.1 is prior stable.
 
 The content is consumed by AI coding agents reading these files directly from a checkout — **there is no MCP server in this repository, and none is required**. Cursor applies `rules/*.mdc` automatically wherever their scope globs match and takes skills by name in chat; Claude Code reads `skills/` and `rules/` from the project workspace, or from this repo kept as a referenced checkout. Any agent that can read files in a workspace can use it the same way. There is no build step for the content — edit the Markdown and Python files directly.
 
@@ -106,7 +106,7 @@ per-script exit-code model, are in
 Budget-conformance props. Not examples. Conventions: [`showcase/README.md`](showcase/README.md).
 
 <details>
-<summary><strong>33 showcase pieces</strong> — click to expand the preview grid</summary>
+<summary><strong>34 showcase pieces</strong> — click to expand the preview grid</summary>
 
 <p align="center">
   <a href="showcase/shipping-crate/"><img src="showcase/shipping-crate/preview.webp" width="24%" alt="Shipping crate: a wooden slat crate with iron corner brackets on a dark studio floor, warm wedge on the back wall" /></a>
@@ -142,6 +142,7 @@ Budget-conformance props. Not examples. Conventions: [`showcase/README.md`](show
   <a href="showcase/brazier/"><img src="showcase/brazier/preview.webp" width="24%" alt="Brazier: an iron fire bowl with a rolled rim on three S-curved forged legs, holding ash and a heap of glowing charcoal, on a dark studio floor" /></a>
   <a href="showcase/apothecary-shelf/"><img src="showcase/apothecary-shelf/preview.webp" width="24%" alt="Apothecary shelf: a stained wooden shelf unit with an arched crest, gallery rails and three drawers, stocked with labelled glass bottles, flasks and glazed jars, on a dark studio floor" /></a>
   <a href="showcase/wooden-yoke/"><img src="showcase/wooden-yoke/preview.webp" width="24%" alt="Wooden yoke: a carved oak ox yoke with upturned ends standing on two bent hickory oxbows pinned above the beam, with an iron ring hung under its centre, on a dark studio floor" /></a>
+  <a href="showcase/butter-churn/"><img src="showcase/butter-churn/preview.webp" width="24%" alt="Butter churn: a tall staved oak churn narrowing toward the top, bound by three iron hoops, with a two-board lid and a maple dasher handle rising through it, on a dark studio floor" /></a>
 </p>
 
 [`shipping-crate`](showcase/shipping-crate/) — procedural crate through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets. Falsifier `--skip-decimate` exits 9.
@@ -206,6 +207,8 @@ Budget-conformance props. Not examples. Conventions: [`showcase/README.md`](show
 
 [`wooden-yoke`](showcase/wooden-yoke/) — procedural double ox yoke on two bent hickory bows with a hung ring, whose neck openings are measured between the bow legs and up to the saddles, through the same pipeline. Falsifiers `--pinch-bows` exits 19, `--edge-on-ring` exits 17.
 
+[`butter-churn`](showcase/butter-churn/) — procedural staved plunge churn whose dasher stroke is recomputed from the inner wall read off the staves and the plunger's reach, through the same pipeline. Falsifiers `--wide-dasher` exits 20, `--tight-hole` exits 18.
+
 </details>
 
 ## Examples

ROADMAP.md

@@ -138,9 +138,9 @@ Not committed; target list for the next content version. (v0.3.0 shipped the smo
 - ~~Brazier (iron bowl on legs, coals, ash) as a game-prop showcase piece~~ **SHIPPED** as `showcase/brazier/` — spun bowl with a rolled rim, three one-sweep forged legs, ash bed biting the wall, 36 cleaved coals packed without interpenetration; tip angle from a density-weighted mass centre and the support polygon, `--tuck-legs` exits 19 on it while the feet still ground
 - ~~Apothecary shelf (shelf unit, bottles and jars of varied form) as a game-prop showcase piece~~ **SHIPPED** as `showcase/apothecary-shelf/` — housed shelves, gallery rails, lapped back boards, a drawer bank and an arched crest, stocked with fifteen lathed vessels in five forms, each corked or lidded and labelled on its own rings; per-vessel headroom under the member above is read off the mesh, `--tall-flask` exits 20 on it while every seat and the envelope still pass
 - ~~Wooden yoke (oxbow, iron rings) as a game-prop showcase piece~~ **SHIPPED** as `showcase/wooden-yoke/` — lofted oak beam with neck saddles and upturned ends, two bent-hickory bows through it and pinned above it, a staple and a threaded hung ring; each neck opening measured between the bow legs and up to the saddle, `--pinch-bows` exits 19 on it while the bows still ground and the envelope is unchanged
-- Ox cart tongue or plough beam that hitches to the yoke's ring as a game-prop showcase piece — a hitch is a ring-on-hook contact the yoke's hung ring only tests against a fixed bar
-- Butter churn (staved tub, lid, dasher) as a game-prop showcase piece
+- ~~Butter churn (staved tub, lid, dasher) as a game-prop showcase piece~~ **SHIPPED** as `showcase/butter-churn/` — sixteen tapered staves with canted ends, three hoops seated vertex-for-vertex on them, a three-board bottom in a croze, a two-board lid and a cross dasher; the plunge stroke is recomputed from the inner wall and the plunger's reach, `--wide-dasher` exits 20 on it while the plunger still clears the staves at rest
 - Bookshelf with leaning books (upright and toppled volumes of varied size, one leaning on its neighbour) as a game-prop showcase piece — the lean needs a contact budget the apothecary shelf's upright vessels never exercised: each leaning book rests on its neighbour's spine edge and on the shelf, not in either
+- Ox cart tongue or plough beam that hitches to the yoke's ring as a game-prop showcase piece — a hitch is a ring-on-hook contact the yoke's hung ring only tests against a fixed bar
 - ~~Small modular kit showcase on recognizable geometry (`modular-kit-snap` contract)~~ **SHIPPED** as `showcase/fence-kit/` — tiling post-and-rail section (AABB X is the tile width; does not re-witness the snap contract); `--skip-decimate` exits 9 on the LOD1 ratio band
 
 - ~~Custom ID-property delete witness~~ **SHIPPED** as `examples/cross-version-property-delete/` — IDs built via `bpy.data.objects.new` (not `active_object`); `property_unset` is TypeError and leaves the key; `del` removes it on 4.5 LTS and 5.x