feat(render) Campaign FW1: doorway-still conformant - deg_mul is dynamic

Render::deg_mul is auto-tuned by frame load and SWUNG between oracle
captures: doorway-still ran right after the heavy terrace-edge capture
with the multiplier depressed (mul <= 0 puts thresholds at/below ideal,
so 001e/0026/002f select the portless level 1 - retail's zero look-in
floods, reproduced exactly at mul = 0), while every other fixture pins
~ +0.99 (thresholds at max). The recon session's "-0.99" live dump was
real - taken under the same cdb load. RetailFrameWalk now exposes the
multiplier; the doorway test pins 0, the rest use the default.

foundry-entry: frames 1-66 reproduce exactly; the F67-F79 standing
segment diverges ONLY in building 0036's intra-building DC order
(retail 116,118,11d vs replay 11d,116,118). The BSP-traversal microscope
pins the flip to 0036's ROOT plane (N=(0,0,-1) D=2.8): replay eye z
2.33 (d=+0.47, NEG-first) vs retail behaving as d<0 (POS-first) - a
structural ~0.5 m frame question (positionPush(2)/part-scale), only
adjudicable live. Turnkey probe:
tools/walk-oracle/fw1-f67-viewpoint-probe.cdb.

Fixture status: nine of ten fully conformant; foundry-entry exact
through F66 with the 13-frame order segment parked on the probe.
Suites: Walk 127/1 skip; hermetic 6,687/0.

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

src/AcDream.App/Rendering/Walk/RetailFrameWalk.cs

@@ -59,6 +59,15 @@ public sealed class RetailFrameWalk
     /// regardless of per-cell visibility.</summary>
     public bool AlwaysDrawObjects = true;
 
+    /// <summary>Retail global <c>Render::deg_mul</c> — DYNAMIC: the
+    /// auto-tuner (<c>auto_update_deg_mul</c>) swings it with frame load
+    /// (positive ⇒ degrade thresholds slide toward each level's max;
+    /// negative ⇒ toward its min). The oracle captures pin ≈+0.99 for every
+    /// fixture except doorway-still, whose capture ran under cdb load with
+    /// the multiplier depressed (the recon session's live dump read −0.99
+    /// under the same conditions).</summary>
+    public float DegradeMultiplier = WalkBuilding.DefaultDegradeMultiplier;
+
     /// <summary>The per-frame root (<c>SmartBox::RenderNormalMode</c>).
     /// <paramref name="cameraCell"/> may be null only when the camera is
     /// outdoors.</summary>
@@ -153,7 +162,9 @@ public sealed class RetailFrameWalk
         // Retail walks the CURRENT degrade level's drawing BSP
         // (part->gfxobj[deg_level]); a degraded-out slot skips everything
         // after publishing the portal list.
-        WalkBspNode? bsp = building.SelectDrawingBsp(ctx.ViewerDistanceTo(building));
+        WalkBspNode? bsp = building.SelectDrawingBsp(
+            ctx.ViewerDistanceTo(building),
+            degradeMultiplier: DegradeMultiplier);
         if (bsp is null) return;
 
         int viewCount = Math.Max(activeViews.ViewCount, 0);