feat: add vse-gamma-cross example witnessing the blend-curve closed form

.cursor-plugin/plugin.json

@@ -86,6 +86,7 @@
     "examples/uv-layer-grid",
     "examples/vertex-weight-limit",
     "examples/vse-cut-list",
+    "examples/vse-gamma-cross",
     "examples/wave-displace"
   ]
 }

.github/workflows/blender-smoke.yml

@@ -427,3 +427,13 @@ jobs:
           # re-imported rig. Exits non-zero on failure.
           xvfb-run -a "$BLENDER" --background \
             --python examples/gltf-skin-roundtrip/gltf_skin_roundtrip.py --
+
+      - name: Shipped example - VSE gamma cross (blend-curve closed form)
+        run: |
+          set -euo pipefail
+          # Check only: renders tiny frames across a GAMMA_CROSS and asserts
+          # every sample against the gamma-0.5 closed form ((1-t)*sqrt(A) +
+          # t*sqrt(B))^2 with t = (frame-start)/duration, plus the material
+          # lerp deviation at mid. Exits non-zero on failure.
+          xvfb-run -a "$BLENDER" --background \
+            --python examples/vse-gamma-cross/vse_gamma_cross.py --

README.md

@@ -18,7 +18,7 @@
 </p>
 
 <p align="center">
-  <strong>12 skills</strong> &nbsp;&bull;&nbsp; <strong>6 rules</strong> &nbsp;&bull;&nbsp; <strong>2 templates</strong> &nbsp;&bull;&nbsp; <strong>17 snippets</strong> &nbsp;&bull;&nbsp; <strong>28 examples</strong>
+  <strong>12 skills</strong> &nbsp;&bull;&nbsp; <strong>6 rules</strong> &nbsp;&bull;&nbsp; <strong>2 templates</strong> &nbsp;&bull;&nbsp; <strong>17 snippets</strong> &nbsp;&bull;&nbsp; <strong>29 examples</strong>
 </p>
 
 <p align="center">
@@ -36,7 +36,7 @@
 
 ## Overview
 
-This repository ships **12 skills, 6 rules, 2 templates, 17 snippets, and 28 runnable examples** for Blender Python development targeting Blender 5.1 (current stable) with Blender 4.5 LTS fallback support.
+This repository ships **12 skills, 6 rules, 2 templates, 17 snippets, and 29 runnable examples** for Blender Python development targeting Blender 5.1 (current stable) with Blender 4.5 LTS fallback support.
 
 The content is consumed by AI coding agents (Cursor, Claude Code, any MCP-capable client) when working on Blender add-ons, geometry nodes scripts, batch pipelines, or animation tooling. There is no build step. Edit the markdown and Python files directly.
 
@@ -186,7 +186,7 @@ byte images stay straight 8-bit. Also witnesses `EXR color_mode='RGB'` dropping
 </details>
 
 <details>
-<summary><strong>Mesh, curves &amp; text</strong> — 8 examples</summary>
+<summary><strong>Mesh, curves &amp; text</strong> — 9 examples</summary>
 
 <table>
 <tr>
@@ -306,6 +306,22 @@ ending in `length=` vs `frame_end=`, and `left_handle`/`right_handle`/`duration`
 the deprecated `frame_final_*`. Asserts closed-form spans, GC wiring and clamping, the
 consumed-input compositing contract, and a save/reload round-trip.
 
+</td>
+</tr>
+<tr>
+<td width="46%" valign="middle">
+<a href="examples/vse-gamma-cross/"><img src="examples/vse-gamma-cross/preview.webp" alt="VSE gamma cross: a mixing bench in a dark studio - eight emissive panels fading crimson to teal across the cross, with the brighter naive-lerp midpoint framed in hazard orange on the console below" /></a>
+</td>
+<td valign="middle">
+
+### [vse-gamma-cross](examples/vse-gamma-cross/)
+
+The GAMMA_CROSS fade is not the naive linear mix: it blends in a gamma-0.5
+space, `((1-t)·√A + t·√B)²` with `t = (frame − start) / duration` — never 1
+inside the effect. Per-frame sample renders assert the closed form (mid dips
+0.115 below the sRGB lerp), and the AgX-default sampling trap is documented
+(`view_transform = 'Standard'` is mandatory for any pixel witness).
+
 </td>
 </tr>
 </table>

ROADMAP.md

@@ -110,7 +110,7 @@ Not committed; target list for the next content version. (v0.3.0 shipped the smo
 - UV-handle lifetime snippet: re-fetch attribute/UV layers by name after any CustomData-reallocating call (`calc_tangents`, `VertexGroup.add`, modifier edits) — held handles dangle silently on 4.5, survive by luck on 5.1 (found authoring `triangulate-tangents`)
 - glTF skinned-mesh export witness: follow-up to `gltf-export-roundtrip` + `vertex-weight-limit` — **SHIPPED** as `examples/gltf-skin-roundtrip/` — `skins[0].joints` names every bone, JOINTS_0/WEIGHTS_0 with unit sums (3e-8), weights bit-exact, rest matrices to 2.4e-07, deformation to 4.8e-07; exporter welds duplicate loops (sorted-multiset comparisons mispair — compare by rest-key); unparented skinned meshes make the exporter bind an armature by name
 - Degenerate-bevel weld hazard (snippet or rule): bevel width ≥ half a box dimension creates zero-area faces whose loops weld on glTF export (found authoring `gltf-export-roundtrip`, where the count check caught a 36-vertex weld)
-- GAMMA_CROSS blend-curve witness: the cross blend is not the naive linear mix (mid-cross measured (0.341, 0.349, 0.463) from crimson (0.85, 0.10, 0.22) and teal (0.06, 0.75, 0.80)) — derive and assert the gamma-space closed form per frame; follow-up to `vse-cut-list`
+- ~~GAMMA_CROSS blend-curve witness~~ **SHIPPED** as `examples/vse-gamma-cross/` — the cross blends in a gamma-0.5 space: `((1-t)·√A + t·√B)²` with `t = (frame − start)/duration`, never 1 inside the effect; mid-cross dips 0.115 below the sRGB lerp from crimson/teal (closed form (0.341, 0.349, 0.463) confirmed per frame); AgX-default sampling poisons the fit (0.146 red-channel error, `view_transform='Standard'` mandatory); deleting a consumed input orphans-and-deletes the effect — follow-up to `vse-cut-list`
 - Falsy `bpy_prop_collection` trap snippet: an empty collection is falsy, so `editor.strips or editor.sequences` silently falls through to the legacy accessor on an empty timeline — always branch on `hasattr`; likely generalizes across the API (found authoring `vse-cut-list`)
 
 ## Future (uncommitted)

docs/gallery/index.html

@@ -513,6 +513,17 @@ <h2><a href="gltf-skin-roundtrip/">gltf-skin-roundtrip</a></h2>
           <a class="card-link" href="gltf-skin-roundtrip/">View example <span aria-hidden="true">&rarr;</span></a>
         </div>
       </article>
+      <article class="card" data-tags="sequencer rendering">
+        <a class="card-media" href="vse-gamma-cross/" aria-label="vse-gamma-cross example detail page">
+          <img src="assets/vse-gamma-cross-hero.webp" alt="vse-gamma-cross — The GAMMA_CROSS fade is not the naive linear mix: it blends in a gamma-0.5 space, so the mid-cross dips below the sRGB lerp." loading="lazy" decoding="async" />
+        </a>
+        <div class="card-body">
+          <h2><a href="vse-gamma-cross/">vse-gamma-cross</a></h2>
+          <p class="teaches">The GAMMA_CROSS fade is not the naive linear mix: it blends in a gamma-0.5 space, so the mid-cross dips below the sRGB lerp. Tiny per-frame renders are asserted against the closed form per frame.</p>
+          <p class="witnesses"><span class="tag">witnesses</span> out = ((1-t)*sqrt(A) + t*sqrt(B))^2 with t = (frame - start) / duration, never 1 inside the effect. The mid lerp deviation is 0.115; AgX-default sampling poisons the fit (Standard is mandatory).</p>
+          <a class="card-link" href="vse-gamma-cross/">View example <span aria-hidden="true">&rarr;</span></a>
+        </div>
+      </article>
     </div>
   </main>
   <footer>