test(physics): Phase W triage — fix stale Path6/tick-gate/ComputeOffset tests (behavior changed by L.3.2/L.4/L.5)

Four tests were asserting pre-change behavior after intentional production
changes:

#2 BSPStepUpTests.C3_Path6_AirborneMoverHitsSteepSlope_SetsCollide
  b1af56e (L.4, 2026-04-30) added a steep-normal gate in Path 6 that
  fires BEFORE SetCollide. Airborne sphere hitting steep poly now returns
  Slid + Collide=false (slide-tangent interim fix). Updated assertion +
  renamed to ReturnsSlid.

#7 PlayerMovementControllerTests.Update_ForwardInput_MovesInFacingDirection
#8 DispatcherToMovementIntegrationTests.Dispatcher_W_held_produces_forward_motion
  235de33 (L.5, 2026-04-30) added _physicsAccum accumulator gate: a single
  Update(1.0f) only integrates one MaxQuantum (0.1s ~ 0.312m at walk speed),
  not the full 1s. Time is carried in accumulator (not dropped). Fixed both
  tests to loop Update(MaxQuantum) for ~11 ticks to accumulate >2m of real
  forward motion, preserving the original distance-threshold assertion intent.

#9 PositionManagerTests.ComputeOffset_BothActive_Combined
  842dfcd (L.3.2, 2026-05-03) changed ComputeOffset from additive
  (rootMotion + correction) to replace semantics: when AdjustOffset returns
  non-zero, it REPLACES root motion (retail Frame::operator= semantics).
  offset.Y = 0 (not 0.4); root motion is dropped when catch-up engages.
  Updated assertion and renamed to CorrectionReplacesRootMotion.

Suite: 9 failures → 5 (only the 5 known-bug tests remain red).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/AcDream.Core.Tests/Physics/BSPStepUpTests.cs

@@ -396,14 +396,18 @@ public class BSPStepUpTests
 
     /// <summary>
     /// Airborne mover descending toward a steep slope (normal.Z &lt; FloorZ):
-    /// Path 6 should still set the Collide flag (it fires for any polygon hit,
-    /// walkable or not).
+    /// Path 6 returns <see cref="TransitionState.Slid"/> and does NOT set
+    /// the Collide flag — the steep-normal slide-tangent branch (L.4,
+    /// commit b1af56e, 2026-04-30) intercepts the hit before SetCollide is
+    /// called and projects the move along the steep face instead, keeping the
+    /// body airborne with the falling animation.
     ///
-    /// <para>Retail: set_collide fires unconditionally when sphere_intersects_poly
-    /// hits; the walkable check happens later in the Collide-flag handler.</para>
+    /// <para>This is a documented intentional deviation from retail (retail calls
+    /// set_collide unconditionally; our interim port uses slide-tangent while
+    /// the retail step_up_slide / cliff_slide chain port is completed).</para>
     /// </summary>
     [Fact]
-    public void C3_Path6_AirborneMoverHitsSteepSlope_SetsCollide()
+    public void C3_Path6_AirborneMoverHitsSteepSlope_ReturnsSlid()
     {
         var (root, resolved) = BSPStepUpFixtures.SlopedUnwalkable();
 
@@ -423,11 +427,13 @@ public class BSPStepUpTests
             root, resolved, t, localSphere, null,
             currPos, Vector3.UnitZ, 1.0f);
 
-        // After L.2.2: Collide flag set, Adjusted returned.
-        // Currently: Slid (wall-slide).
-        Assert.Equal(TransitionState.Adjusted, result);
-        Assert.True(t.SpherePath.Collide,
-            "Expected Collide flag set when airborne sphere hits slope (L.2.2)");
+        // L.4 slide-tangent (b1af56e, 2026-04-30): steep polygon hit by
+        // airborne sphere returns Slid (not Adjusted) and does NOT set
+        // the Collide flag — the into-wall displacement is removed and
+        // CollisionNormal/SlidingNormal are set instead.
+        Assert.Equal(TransitionState.Slid, result);
+        Assert.False(t.SpherePath.Collide,
+            "Collide must NOT be set when the L.4 steep-slope slide-tangent fires");
     }
 
     // =========================================================================

tests/AcDream.Core.Tests/Physics/PositionManagerTests.cs

@@ -120,11 +120,18 @@ public sealed class PositionManagerTests
     }
 
     // =========================================================================
-    // Test 5: both sources active — combined delta
+    // Test 5: both sources active — correction REPLACES root motion
+    //
+    // retail-faithful semantics (842dfcd, L.3.2, 2026-05-03):
+    // when InterpolationManager.AdjustOffset returns a non-zero correction,
+    // ComputeOffset returns the correction alone — it does NOT add root
+    // motion on top. Mirrors retail's PositionManager::adjust_offset
+    // (acclient @ 0x00555190) which calls Frame::operator= to OVERWRITE
+    // the rootOffset frame when catch-up engages.
     // =========================================================================
 
     [Fact]
-    public void ComputeOffset_BothActive_Combined()
+    public void ComputeOffset_BothActive_CorrectionReplacesRootMotion()
     {
         var pm     = Make();
         var interp = new InterpolationManager();
@@ -132,9 +139,9 @@ public sealed class PositionManagerTests
         // Enqueue target 1m ahead on +X
         interp.Enqueue(new Vector3(1f, 0f, 0f), heading: 0f, isMovingTo: false);
 
-        // rootMotion = (0, 4, 0) × 0.1 = (0, 0.4, 0)
-        // correction ≈ (0.8, 0, 0)
-        // combined ≈ (0.8, 0.4, 0)
+        // correction ≈ (0.8, 0, 0) — replaces root motion (0, 0.4, 0).
+        // retail-faithful: correction overwrites root motion, Y is dropped.
+        // (842dfcd, 2026-05-03: switched from additive to replace semantics)
         Vector3 offset = pm.ComputeOffset(
             dt: 0.1,
             currentBodyPosition: Vector3.Zero,
@@ -144,7 +151,7 @@ public sealed class PositionManagerTests
             maxSpeed: 4f);
 
         Assert.Equal(0.8f, offset.X, precision: 3);
-        Assert.Equal(0.4f, offset.Y, precision: 3);
+        Assert.Equal(0f,   offset.Y, precision: 3);   // root motion dropped — correction replaces
         Assert.Equal(0f,   offset.Z, precision: 3);
     }