fix(physics): #345 — a grounded mover glides along a too-steep face; validate_walkable's return is scoped as retail's bytes scope it

Retail's OBJECTINFO::validate_walkable @0x0050d010 initializes its
return slot to OK (0x0050d025) and assigns ADJUSTED only inside the
below-plane guard, immediately after the push executes (0x0050d249).
The guard-fail path — grounded, OnWalkable, plane too steep — jumps
past the contact write, the push, and the assignment (0x0050d1b9 ->
0x0050d251): retail deliberately IGNORES the steep plane at primary
validation so the insert proceeds, the step-down phase fails on the
steep landing, and the edge family produces the per-tick lateral
glide. ACE flattened this into an unconditional return Adjusted
(ObjectInfo.cs:169) and we inherited it; our TransitionalInsert then
retried the byte-identical Adjusted forever — the user's
stop-instead-of-slide.

Evidence chain: the user's retail observation (the axiom), the live
cdb glide profile (edge_slide/cliff_slide 594 each in lockstep,
step_up 0), the D0 implementer's correct STOP (fixtures reproduced
the stuck fingerprint while faithfully executing the ACE-shaped
reading — refuting the reading, not the code), and the capstone
byte-decode both Opus reviewers re-derived independently, including
the stack-slot frame arithmetic and every ret site's eax.

The conformance fixture is the live topology: flat and steep terrain
triangles sharing ONE cell's diagonal (a cell-boundary face does NOT
reproduce the loop — the cell-scoped primary sample never validates a
neighbour's triangle — and is pinned as supplementary). Sabotage:
restoring the unconditional Adjusted reds the discriminator with the
exact stuck position (0.325 m lateral, 28/30 stuck ticks vs 2.602 m /
14/30 fixed; reviewer B's independent five-angle table is monotone
10-85 degrees). Stuck ticks are counted from positions so the
assertion survives the eventual probe strip.

In-game glide gate PASSED 2026-08-08: "Well it works, we are sliding.
I cant detect any speed change from retail."

Filed alongside: #347 + AD-70 (our glide alternates arm/move at half
retail's per-tick rate — retail redirects within the tick; next up by
user direction), AD-71 (the guard's mutable WalkableAllowance operand
vs retail's fixed is_valid_walkable global — now return-value-bearing),
and the reviewers' named residuals in the #345 closure entry
(placement-arm flip, other-cell coverage gap, EdgeSlide-less
projectiles, ACE's server-side shared misport predicting remote
drift-then-snap on steep terrain). The unported IsViewer arm of
validate_walkable is noted in the D0 doc.

Suite: clean-room complete solution 11,271 passed / 4 skipped / 0
failed; Core assembly re-run green after the review-driven test
hardening.

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

src/AcDream.Core/Physics/TransitionTypes.cs

@@ -3743,6 +3743,15 @@ public sealed class Transition
         // contactPlane.Normal.Z is 1 for flat ground, so this is just dist.
         float zDist = dist / contactPlane.Normal.Z;
 
+        // Retail 0x0050d025/0x0050d249: the return value starts OK and
+        // becomes Adjusted ONLY when the push below executes. A grounded
+        // mover already OnWalkable dipping below a TOO-STEEP plane skips
+        // the whole block (0x0050d1b9 -> 0x0050d251) and returns OK —
+        // primary validation deliberately ignores the steep face so the
+        // insert proceeds and the step-down failure routes into the
+        // edge-slide family (#345: retail's glide-along-steep-slope).
+        // ACE's unconditional Adjusted here is a misport.
+        var result = TransitionState.OK;
         bool walkable = contactPlane.Normal.Z >= sp.WalkableAllowance;
         if (sp.StepDown || !oi.OnWalkable || walkable)
         {
@@ -3751,7 +3760,8 @@ public sealed class Transition
 
             if (sp.StepDown)
             {
-                // Validate step-down interpolation factor.
+                // Validate step-down interpolation factor
+                // (failure returns Collided: retail 0x0050d28b).
                 float interp = (1f - (-1f / (sp.StepDownAmt * sp.WalkInterp)) * zDist) * sp.WalkInterp;
                 if (interp >= sp.WalkInterp || interp < -0.1f)
                 {
@@ -3766,6 +3776,7 @@ public sealed class Transition
 
             // Push the sphere up out of the terrain.
             sp.AddOffsetToCheckPos(new Vector3(0f, 0f, -zDist));
+            result = TransitionState.Adjusted;
         }
 
         // #345 probe (2026-08-08): named local, same rationale as
@@ -3780,9 +3791,9 @@ public sealed class Transition
         PhysicsDiagnostics.TraceTransitValidateWalkable(
             oi.SelfEntityId, "below-push", dist, waterDepth,
             oi.Contact, sp.StepDown, belowPushGuardPassed,
-            contactPlane.Normal, TransitionState.Adjusted);
+            contactPlane.Normal, result);
 
-        return TransitionState.Adjusted;
+        return result;
     }
 
     private static void CacheWalkableContext(