fix(anim): remove frame swap — cursor now traverses all frames in reverse

ROOT CAUSE of "twitching" / stuck-on-frame-0 for reverse animations
(TurnRight with negative dat framerate, StrafeRight, etc.):

The frame swap (StartFrame↔EndFrame for negative speed) made EndFrame=0,
and GetStartFramePosition returned (0+1)-eps = 0.999. The cursor
oscillated between 0.0 and 0.999 — floor() of anything in [0,1) is
always 0, so only frame 0 ever rendered.

Fix: DON'T swap. Keep StartFrame=0, EndFrame=N-1 regardless of speed
sign. GetStartFramePosition for negative speed returns (N-1+1)-eps ≈ N,
so the cursor starts near the high end and counts down through ALL
frames. The Advance loop's reverse boundary check uses StartFrame (the
low value) correctly without the swap.

Also strips diagnostic logging from AnimationSequencer and GameWindow.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/AcDream.Core/Physics/AnimationSequencer.cs

@@ -170,6 +170,10 @@ public sealed class AnimationSequencer
     /// <summary>Current cyclic motion command.</summary>
     public uint CurrentMotion { get; private set; }
 
+    // Diagnostics
+    public int QueueCount => _queue.Count;
+    public bool HasCurrentNode => _currNode != null;
+
     // ── Private state ────────────────────────────────────────────────────────
 
     private readonly Setup _setup;
@@ -379,11 +383,10 @@ public sealed class AnimationSequencer
             else
             {
                 // ── REVERSE PLAYBACK ─────────────────────────────────────
-                // After FUN_005267E0 swaps low↔high for negative speed:
-                //   StartFrame = high (e.g. 3), EndFrame = low (e.g. 0)
-                // GetStartFramePosition placed cursor at (EndFrame+1)-eps ≈ 0.99999.
-                // The cursor counts DOWN toward EndFrame. Boundary = EndFrame.
-                double minBoundary = (double)curr.EndFrame;
+                // No swap: StartFrame is still the LOW value (e.g. 0).
+                // GetStartFramePosition placed cursor at (EndFrame+1)-eps (near high).
+                // The cursor counts DOWN toward StartFrame.
+                double minBoundary = (double)curr.StartFrame;
                 if (newPos <= minBoundary)
                 {
                     // How much time spilled past the lower boundary?
@@ -485,21 +488,13 @@ public sealed class AnimationSequencer
 
         double fr = (double)ad.Framerate * (double)speedMod;
 
-        // ── FUN_005267E0 multiply_framerate ──────────────────────────────
-        // When speed is negative (TurnLeft→TurnRight, SideStepLeft→SideStepRight),
-        // swap Low↔High so the advance loop counts DOWN from the swapped EndFrame
-        // toward the swapped StartFrame.  The pseudocode says:
-        //   if speedScale < 0: swap startFrame ↔ endFrame
-        if (fr < 0.0)
-        {
-            (low, high) = (high, low);
-            // After swap: StartFrame > EndFrame (the loop detects delta < 0 and
-            // uses StartFrame as the lower boundary to count down toward).
-        }
-        else
-        {
-            if (low > high) high = low; // clamp for positive-speed case only
-        }
+        // Do NOT swap StartFrame↔EndFrame for negative speed.
+        // The Advance loop handles negative delta by checking against
+        // StartFrame as the lower boundary. GetStartFramePosition uses
+        // EndFrame (the HIGH value) to start the cursor near the top
+        // for reverse playback, so the cursor traverses all frames
+        // from high→low instead of being stuck in [0,1).
+        if (low > high) high = low;
 
         return new AnimNode(anim, fr, startFrame: low, endFrame: high, isLooping);
     }

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

@@ -456,13 +456,12 @@ public sealed class AnimationSequencerTests
         // CurrentMotion should record the original TurnLeft command.
         Assert.Equal(TurnLeft, seq.CurrentMotion);
 
-        // After FUN_005267E0 (multiply_framerate) swaps low↔high for negative speed:
-        //   StartFrame = 3 (was high), EndFrame = 0 (was low)
-        // GetStartFramePosition for negative speed = (EndFrame + 1) - EPSILON = (0+1) - eps ≈ 0.99999.
-        // The cursor starts just below frame 1 and counts DOWN toward EndFrame(=0).
+        // Without swap: StartFrame=0, EndFrame=3 (original range preserved).
+        // GetStartFramePosition for negative speed = (EndFrame+1)-eps = (3+1)-eps ≈ 3.99999.
+        // The cursor starts near the HIGH end and counts DOWN toward StartFrame(=0).
         double pos = GetFramePosition(seq);
-        Assert.True(pos > 0.9 && pos < 1.0,
-            $"Expected framePosition near 0.99999 (reverse start near EndFrame+1) but got {pos}");
+        Assert.True(pos > 3.9 && pos < 4.0,
+            $"Expected framePosition near 3.99999 (reverse start near EndFrame+1) but got {pos}");
     }
 
     [Fact]