fix(examples): redesign gn-modifier-inputs as three GN spiral staircases (#274)

The gallery review judged the hero programmer art: three plain cubes of
different size and colour, the largest cropped and flat-lit. The shared
Geometry Nodes tree now builds a parametric spiral staircase from its one
Float input (renamed Scale -> Height; still Socket_1): step count =
round((Height - 0.3) / 0.1), oak treads with brass balusters instanced up
a helix, a teal newel post and a brass helical handrail. Heights 1/2/3 m
give 7/17/27 treads, so the three modifiers on one tree read left to right
as one design at three settings of one input. A lost write collapses a
tall staircase to the 7-step default, which the render would show.

The check contract is unchanged: shared node_group, per-version write
path (dict on 4.5/5.1, mod.properties.inputs on 5.2), readback, evaluated
Z-extent == written value (the newel post spans exactly [0, Height]),
zmin == 0, distinct extents. --same-height is the falsifier flag;
--same-scale stays as an alias. Lighting: shaped key (36 deg spread) and a
high rim so the foreground floor stays dark. Adds an asset-sheet SELECT row.

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

@@ -580,15 +580,16 @@ verts = 72, faces = 54, and `Set Material` carries the lime accent.
 </tr>
 <tr>
 <td width="46%" valign="middle">
-<a href="examples/gn-modifier-inputs/"><img src="examples/gn-modifier-inputs/preview.webp" alt="GN modifier inputs: three separate cubes in teal, copper, and coral scaled to 1, 2, and 3 meters by a shared Geometry Nodes tree, proving per-modifier Scale writes land on 5.2 RNA and on 4.5 dict assignment" /></a>
+<a href="examples/gn-modifier-inputs/"><img src="examples/gn-modifier-inputs/preview.webp" alt="GN modifier inputs: three spiral staircases from one shared Geometry Nodes tree, 1, 2 and 3 meters tall with 7, 17 and 27 oak treads, proving per-modifier Height writes land on 5.2 RNA and on 4.5 dict assignment" /></a>
 </td>
 <td valign="middle">
 
 ### [gn-modifier-inputs](examples/gn-modifier-inputs/)
 
-One Geometry Nodes tree, three modifier copies. Writes a Float Scale input through
-`mod.properties.inputs` on 5.2 and `mod[identifier]` on 4.5/5.1. Asserts readback and
-evaluated Z-extent equal 1 / 2 / 3. The 5.1 dict form raises TypeError on 5.2.
+One Geometry Nodes spiral-staircase tree, three modifier copies. Writes a Float Height
+input through `mod.properties.inputs` on 5.2 and `mod[identifier]` on 4.5/5.1; the tree
+turns 1 / 2 / 3 m into 7 / 17 / 27 treads. Asserts readback and evaluated Z-extent equal
+1 / 2 / 3. The 5.1 dict form raises TypeError on 5.2.
 
 </td>
 </tr>

docs/gallery/asset-sheets/gn-modifier-inputs.webp

@@ -453,12 +453,12 @@ <h2><a href="gn-instance-grid/">gn-instance-grid</a></h2>
       </article>
       <article class="card" data-tags="geometry-nodes modifiers">
         <a class="card-media" href="gn-modifier-inputs/" tabindex="-1" aria-hidden="true">
-          <img src="assets/gn-modifier-inputs-hero.webp" alt="Three separate cubes stepping up in size from left to right: a small teal cube, an orange block and a large red block." loading="lazy" decoding="async" />
+          <img src="assets/gn-modifier-inputs-hero.webp" alt="Three spiral staircases of one design, with oak treads, teal posts and brass rails, rising left to right from seven steps to seventeen to twenty-seven." loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="gn-modifier-inputs/">gn-modifier-inputs</a></h2>
           <p class="teaches">Per-modifier Geometry Nodes Float inputs on a shared tree — 4.5/5.1 write mod[identifier], 5.2 writes mod.properties.inputs.Socket_1.value.</p>
-          <p class="witnesses"><span class="tag">witnesses</span> The 5.1 dict form raises TypeError on 5.2 rather than silently no-opping; RNA properties are AttributeError on 4.5. Readback and evaluated Z-extent match written scales 1/2/3.</p>
+          <p class="witnesses"><span class="tag">witnesses</span> The 5.1 dict form raises TypeError on 5.2 rather than silently no-opping; RNA properties are AttributeError on 4.5. Readback and evaluated Z-extent match written heights 1/2/3, which the shared tree turns into 7/17/27 treads.</p>
           <a class="card-link" href="gn-modifier-inputs/">View example<span class="sr-only"> gn-modifier-inputs</span> <span aria-hidden="true">&rarr;</span></a>
         </div>
       </article>

docs/gallery/assets/gn-modifier-inputs-hero.webp

@@ -139,8 +139,8 @@
       "name": "gn-modifier-inputs",
       "dir": "examples/gn-modifier-inputs",
       "teaches": "Per-modifier Geometry Nodes Float inputs on a shared tree — 4.5/5.1 write mod[identifier], 5.2 writes mod.properties.inputs.Socket_1.value.",
-      "alt": "Three separate cubes stepping up in size from left to right: a small teal cube, an orange block and a large red block.",
-      "witnessesFix": "The 5.1 dict form raises TypeError on 5.2 rather than silently no-opping; RNA properties are AttributeError on 4.5. Readback and evaluated Z-extent match written scales 1/2/3.",
+      "alt": "Three spiral staircases of one design, with oak treads, teal posts and brass rails, rising left to right from seven steps to seventeen to twenty-seven.",
+      "witnessesFix": "The 5.1 dict form raises TypeError on 5.2 rather than silently no-opping; RNA properties are AttributeError on 4.5. Readback and evaluated Z-extent match written heights 1/2/3, which the shared tree turns into 7/17/27 treads.",
       "hero": "docs/gallery/assets/gn-modifier-inputs-hero.webp",
       "preview": "examples/gn-modifier-inputs/preview.webp",
       "tags": [

docs/gallery/contact-sheets/gn-modifier-inputs-contact-sheet.webp

@@ -1,26 +1,37 @@
 # GN Modifier Inputs
 
-A runnable example that attaches one Geometry Nodes tree to three cubes and
-writes a per-modifier Float **Scale** input through the version-appropriate
-API. The tree scales a 1 m cube by that value and lifts it onto the floor.
-Evaluated Z-extent must match the written scale (1 / 2 / 3). That is the
-closed form: if the write did not land, the three cubes collapse to the
-socket default and the extents are no longer distinct.
+A runnable example that attaches one Geometry Nodes tree to three carrier
+objects and writes a per-modifier Float **Height** input through the
+version-appropriate API. The tree is a parametric spiral staircase: from
+Height it derives the step count (`round((Height - 0.3) / 0.1)`), instances
+the carrier mesh — one bevelled oak tread with its brass baluster — up a
+helix at 22.5° per step, and adds a teal newel post and a brass helical
+handrail. Written heights 1 / 2 / 3 m give 7 / 17 / 27 treads, so the
+three staircases read left to right as one design at three settings of one
+input.
+
+The closed form: the newel post runs from the floor at z=0 to exactly
+z=Height and every other part stays inside that span, so the evaluated
+Z-extent must equal the written height. If a write did not land, that
+staircase falls back to the socket default (1 m, 7 treads) and the extents
+are no longer distinct — in the render, the tall staircases collapse to
+copies of the short one.
 
 **What it witnesses:** Blender 5.2 removed ID-property assignment on
 `NodesModifier`. `mod["Socket_1"] = 2.0` raises `TypeError` rather than
 silently no-opping. 4.5 LTS and 5.1 still require that dict form;
 `mod.properties` does not exist there (`AttributeError`). 5.2+ writes
 `mod.properties.inputs.Socket_1.value`. After the write, the depsgraph
-must be updated or `evaluated_get` still sees the previous scale.
+must be updated or `evaluated_get` still sees the previous height.
 
 Follows [`geometry-nodes-python`](../../skills/geometry-nodes-python/SKILL.md).
 
-Staging: the carriers now stand 0.5 m apart (`XS`). The old spacing
-overlapped the 2 m and 3 m cubes by 0.2 m. The check reads only each
-cube's evaluated Z extent and zmin, never X, so this is layout only. The
-camera looks from the front, so small to large reads left to right, and a
-duller finish keeps the tops from blowing out.
+Staging: the default dark studio. The three staircases stand on 1.62 m
+centres (`XS`); the check reads only each object's evaluated Z extent and
+zmin, never X, so the layout is free. All three share one tree and one set
+of materials — the only thing that differs between them is the modifier
+input. The key carries a 36° spread so its pool stays on the stairs, and
+the rim sits high behind them so it does not wash the foreground floor.
 
 ## Run
 
@@ -29,7 +40,8 @@ duller finish keeps the tops from blowing out.
 blender --background --python gn_modifier_inputs.py --
 
 # Portable falsifier: write 1.0 to every modifier. Must exit non-zero.
-blender --background --python gn_modifier_inputs.py -- --same-scale
+# (--same-scale is kept as an alias for the pre-staircase flag name.)
+blender --background --python gn_modifier_inputs.py -- --same-height
 
 # Force one side of the split (must fail on the other series, not all three):
 blender --background --python gn_modifier_inputs.py -- --api dict
@@ -50,25 +62,29 @@ against it. `10` is the shared framing helper.
 | 0 | Success |
 | 1 | Uncaught exception (FATAL wrapper) |
 | 2 | argparse / usage |
-| 3 | Scale input identifier missing on the tree interface |
+| 3 | Height input identifier missing on the tree interface |
 | 4 | Modifiers do not share one node_group |
 | 5 | Version-path write raised (`--api dict` on 5.2, `--api rna` on 4.5) |
 | 6 | Version-path read raised |
-| 7 | Readback ≠ intended scale (`--same-scale` lands here) |
-| 8 | Evaluated Z-extent ≠ intended scale |
+| 7 | Readback ≠ intended height (`--same-height` lands here) |
+| 8 | Evaluated Z-extent ≠ intended height |
 | 9 | Evaluated mesh not sitting on z=0 |
 | 10 | Gallery framing violation |
 | 11 | Evaluated extents not distinct |
 | 12 | `--output` produced no file |
 
 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).
-Smoke does not pass `--output`, `--same-scale`, or `--api dict`/`rna`.
+Smoke does not pass `--output`, `--same-height`, or `--api dict`/`rna`.
 
 ## Falsification
 
 | Probe | Binary | Result |
 | --- | --- | --- |
 | `--api dict` | 5.2.1 LTS | exit 5, `TypeError: id properties not supported for this type` |
 | `--api rna` | 4.5.11 LTS | exit 5, `AttributeError: 'NodesModifier' object has no attribute 'properties'` |
+| `--api dict` | 5.1.2 | exit 0 (5.1 still takes the dict form) |
+| `--api rna` | 5.1.2 | exit 5, `AttributeError: 'NodesModifier' object has no attribute 'properties'` |
+| `--same-height` | 5.2.1, 5.1.2, 4.5.11 | exit 7, `readback 1.0 != written 2.0 on SpiralStair.H2` |
+| `RAIL_H = -0.5` (treads climb past the post) | 5.2.1, 4.5.11 | exit 8, `evaluated Z-extent 1.934334 != height 1.0` |
 | `--api auto` | 5.2.1, 5.1.2, 4.5.11 | exit 0, extents 1.000 / 2.000 / 3.000 |