docs(render): S3 hygiene lens closeout — the clip-distance doc names every writer; AppendSlot's doc drops the U.4 AABB promise

The hygiene lens's one blocking finding was a sentence the lead's own
§10.6 prescribed: 'only portal_depth.vert writes gl_ClipDistance in the
world pass'. Five mesh/particle vertex shaders still write it from the
per-cell clip-region table PrepareClipFrame publishes (dormant in the walk
path, which feeds slot 0; live for the flat path). The doc now says so.
ClipFrame.AppendSlot's doc still promised a U.4 AABB box that no longer
exists after H1. Comments only; no behavior change.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/AcDream.App/Rendering/ClipFrame.cs

@@ -155,12 +155,13 @@ public sealed class ClipFrame : IDisposable
 
     /// <summary>
     /// Append one clip region (becomes the next slot index) from a
-    /// <see cref="ClipPlaneSet"/>. Only the convex-plane case is supported in
-    /// U.3 — <c>Count &gt; 0</c> packs that many planes; <c>Count == 0</c> packs a
-    /// no-clip region (pass-all). The scissor / nothing-visible fallbacks that
-    /// <see cref="ClipPlaneSet"/> can carry are deferred to U.4 (which will draw
-    /// the AABB box or skip the cell on the CPU side, not via this slot). Returns
-    /// the new slot's index.
+    /// <see cref="ClipPlaneSet"/>: <c>Count &gt; 0</c> packs that many planes;
+    /// <c>Count == 0</c> packs a no-clip region (pass-all) — that is the
+    /// whole contract for both of <see cref="ClipPlaneSet"/>'s empty states
+    /// (nothing visible is decided by the caller before it appends; a plane
+    /// overflow draws unclipped, over-include). There is no scissor and no
+    /// AABB anywhere on this path (S3 landing hygiene, H1). Returns the new
+    /// slot's index.
     /// </summary>
     public int AppendSlot(ClipPlaneSet set)
     {

src/AcDream.App/Rendering/WorldPassSurface.cs

@@ -56,13 +56,19 @@ internal interface IWorldPassSurface
     ///
     /// <para>Vulkan activates every element the shader declares and has no
     /// enable, so this is a no-op there — and that is safe rather than a
-    /// divergence: only <c>portal_depth.vert</c> writes <c>gl_ClipDistance</c>
-    /// in the world pass now (S3 landing hygiene, H4 — S3 chunk 4 fix round 2
-    /// (L3) deleted the sky and terrain shaders' own declaration of the block
-    /// this contract used to also publish; see <see cref="PrepareClipFrame"/>'s
-    /// doc). It still writes <c>1.0</c> ("keep everything") into every slot
-    /// past its active count, so a frame with no clip planes clips nothing on
-    /// either backend (plan §5.5.14 item 4).</para>
+    /// divergence. Two shader families still write <c>gl_ClipDistance</c> in
+    /// the world pass: <c>portal_depth.vert</c> (the exit seals and punch fans,
+    /// planes handed per draw) and the mesh/particle vertex shaders
+    /// (<c>mesh_modern</c>, <c>mesh_atmospheric</c>, <c>mesh_detail</c>,
+    /// <c>particle</c>, <c>particle_mesh</c>), which read the per-cell
+    /// clip-region table this contract publishes through
+    /// <see cref="PrepareClipFrame"/>. The walk feeds every ordinary part and
+    /// every particle slot 0 (no clip), so in the walk path that table is
+    /// dormant; the sky and terrain shaders no longer declare any clip block
+    /// at all (S3 chunk 4 fix round 2, L3). Every writer sets <c>1.0</c>
+    /// ("keep everything") in each slot past its active count, so a frame
+    /// with no clip planes clips nothing on either backend (plan §5.5.14
+    /// item 4).</para>
     /// </summary>
     void EnableClipDistances();