docs(vm1): closeout - AP-232 for the translucent detail blend weight; sampler test pins the production constant

Opus narrow re-review of ae651312: APPROVE. Closes its three residuals:
- AP-232 filed: retail's single-pass stage-1 OUTPUT alpha
  (MODULATE(TEXTURE, CURRENT) @0x0059c549) is the blend weight for a
  translucent subset; acdream's two-draw model is exact for opaque
  subsets (fog identity pinned) and a bounded weight difference on
  translucent ones. Distinct from AP-34 (queue order). Owed since
  05970306.
- TerrainAtlas.DetailSamplerDescription names the production sampler
  (WRAP/LINEAR x3 per ACRender::SetDetailSurfaceInternal @0x006b6280);
  the test now asserts that constant's properties instead of a
  test-local copy.
- Plan VM1 section: fragment now described as fogged; VM1 marked CLOSED
  with the Holtburg measurement (+2.17/+0.57/+0.16 vs predicted
  +2.2/+0.66/+0.16) and the detail-on cost (+0.3-0.5 ms CPU at Arwic).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/plans/2026-08-22-visualmaster-campaign.md

@@ -77,7 +77,7 @@ single-pass path darkens by ~10 %. Neither explains a scene-wide level.
 | Slice | Closes | Gate |
 |---|---|---|
 | VM0 | F1 — default-path invariance | **CLOSED 2026-08-22 — PASS**; [report](../research/2026-08-22-vm0-default-path-invariance.md) |
-| VM1 | F2 — invented detail fade | automated |
+| VM1 | F2/F3 — #226 single-pass re-port + fade removal | **CLOSED 2026-08-22** — `05970306`, `388457a7`, `ae651312`, closeout; Opus APPROVE |
 | VM2 | F3 — which retail detail path ran | **CLOSED 2026-08-22** — single-pass; see [cdb note](../research/2026-08-22-vm2-retail-detail-path-cdb.md) |
 | VM3 | F4 — linear-light post stack | automated + **owner visual** |
 | VM4 | F5 — overclaiming docs, incl. the reviewer's own | docs |
@@ -85,7 +85,7 @@ single-pass path darkens by ~10 %. Neither explains a scene-wide level.
 | VM6 | Foliage wind | automated + **owner visual** |
 | VM7 | Closeout: full gates, register, roadmap, merge | **owner** |
 
-Order is VM2 (done) → VM0 (done) → VM1 → VM4 → VM5 → VM3 → VM6 → VM7. VM0 goes first because everything after it is measured
+Order is VM2 (done) → VM0 (done) → VM1 (done) → VM4 → VM5 → VM3 → VM6 → VM7. VM0 goes first because everything after it is measured
 against the baseline it establishes.
 
 ---
@@ -147,7 +147,7 @@ already converges the live category texture to its 1.033 mean factor.
 **Implementation**
 
 - Delete the two constants and `vDetailFade` from `mesh_detail.vert/.frag`
-  (`mesh_detail.vert:83`); the fragment outputs `detail.rgba` unscaled.
+  (`mesh_detail.vert:83`); the fragment outputs `applyFog(detail.rgb)` with alpha `detail.a * instanceOpacity` — fogged so the two-draw result collapses to retail's fog-after-combine pixel (VM1 review fix).
 - Confirm the detail texture is uploaded with a full mip chain and sampled
   LINEAR/LINEAR/LINEAR, WRAP — that *is* retail's attenuation; test it.
 - Rename `RetailDetailTextureContract` members so nothing un-anchored is
@@ -157,6 +157,8 @@ already converges the live category texture to its 1.033 mean factor.
 - If the owner later wants a ramp back, it returns as a **pack setting**
   (enhancement), never on the default path.
 
+**OUTCOME (2026-08-22): CLOSED.** Four commits: the single-pass re-port + fade removal (`05970306`); the interior shell/detail passes binding their own instance opacity — a pre-campaign stale-slot read (`388457a7`); the Opus fix round — the detail contribution is fogged so the two-draw result collapses to retail's fog-after-combine pixel, mip/sampler test, doc caveats (`ae651312`); and the closeout (AP-232 for the translucent-subset blend weight, the sampler test pinned to the production constant). Measured on Holtburg buildings: predicted +2.2/+0.66/+0.16 levels vs measured +2.17/+0.57/+0.16 (`artifacts/vm1`, grass/sky controls 0.00). Detail-on costs +0.3-0.5 ms CPU / +0.1 ms GPU at dense Arwic, still under the pre-campaign baseline. Opus dual-lens review: APPROVE WITH FIXES -> fix round -> narrow re-review APPROVE.
+
 **Acceptance:** no reference to a distance fade remains in src or the note;
 VM0's masked comparison re-run shows the only change is on detail surfaces;
 at >50 m a building reads the same as at 60 m (mips), not a hard step.

docs/research/2026-08-21-retail-building-detail-texturing-pseudocode.md

@@ -193,7 +193,7 @@ draw weighted by `detail.a * diffuseAlpha` (the pipeline in
 opaque subsets this is identical (both reduce to the base's own alpha
 gating nothing else downstream); on translucent building/EnvCell subsets it
 is a bounded difference in how much the SUBSEQUENT alpha-queue compositing
-sees, already covered by the existing AP-34 shared-alpha-queue divergence
+sees, registered as its own row AP-232 (blend WEIGHT on translucent subsets), distinct from AP-34 (queue ORDER)
 row rather than a new one.
 
 ## Darkening, not brightening

src/AcDream.App/Rendering/TerrainAtlas.cs

@@ -34,6 +34,16 @@ public sealed class TerrainAtlas : IDisposable
     /// one-layer 2-D array so it uses the same backend-neutral table contract
     /// as every other world texture.
     /// </summary>
+    /// <summary>
+    /// Retail's detail-stage sampler: <c>ACRender::SetDetailSurfaceInternal</c>
+    /// (0x006b6280) sets WRAP/WRAP addressing and LINEAR/LINEAR/LINEAR filtering
+    /// on the detail stage. The LINEAR mip chain is retail's only distance
+    /// attenuation for built meshes (VM1), so this constant is load-bearing and
+    /// pinned by <c>TerrainAtlasDetailTextureTests</c>.
+    /// </summary>
+    internal static readonly GpuSamplerDescription DetailSamplerDescription =
+        GpuSamplerDescription.WorldRepeat;
+
     internal readonly record struct RetailDetailTextureBinding(
         GpuTextureSlot TextureSlot,
         float Tiling,
@@ -430,7 +440,7 @@ public sealed class TerrainAtlas : IDisposable
             // ChangeRegion and the only reachable SmartBox caller keep
             // landscape (0) and object (3) disabled, so do not create or expose
             // those categories here.
-            detailSampler = device.CreateSampler(GpuSamplerDescription.WorldRepeat);
+            detailSampler = device.CreateSampler(DetailSamplerDescription);
             if (terrainDesc is { Count: > 1 })
             {
                 buildingDetail = TryCreateDetailTexture(

tests/AcDream.App.Tests/Rendering/TerrainAtlasDetailTextureTests.cs

@@ -65,7 +65,10 @@ public sealed class TerrainAtlasDetailTextureTests
             },
         };
 
-        IGpuSampler sampler = device.CreateSampler(GpuSamplerDescription.WorldRepeat);
+        // The sampler is created from the PRODUCTION constant so that changing
+        // TerrainAtlas's choice (e.g. to a clamp sampler) fails the property
+        // assertions below rather than being forwarded unnoticed.
+        IGpuSampler sampler = device.CreateSampler(TerrainAtlas.DetailSamplerDescription);
 
         MethodInfo method = typeof(TerrainAtlas).GetMethod(
             "TryCreateDetailTexture",
@@ -92,7 +95,7 @@ public sealed class TerrainAtlasDetailTextureTests
         // point-filtered UI sampler.
         GpuRecordedTextureRegistration registration = Assert.Single(
             device.Calls.OfType<GpuRecordedTextureRegistration>());
-        Assert.Equal(GpuSamplerDescription.WorldRepeat, registration.Sampler);
+        Assert.Equal(TerrainAtlas.DetailSamplerDescription, registration.Sampler);
         Assert.Equal(GpuFilter.Linear, registration.Sampler.MinFilter);
         Assert.Equal(GpuFilter.Linear, registration.Sampler.MagFilter);
         Assert.Equal(GpuMipFilter.Linear, registration.Sampler.MipFilter);