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:
+                // No swap: StartFrame is still the LOW value (e.g. 0).
-                //   StartFrame = high (e.g. 3), EndFrame = low (e.g. 0)
+                // GetStartFramePosition placed cursor at (EndFrame+1)-eps (near high).
-                // GetStartFramePosition placed cursor at (EndFrame+1)-eps ≈ 0.99999.
+                // The cursor counts DOWN toward StartFrame.
-                // The cursor counts DOWN toward EndFrame. Boundary = EndFrame.
+                double minBoundary = (double)curr.StartFrame;
-                double minBoundary = (double)curr.EndFrame;
                 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 ──────────────────────────────
+        // Do NOT swap StartFrame↔EndFrame for negative speed.
-        // When speed is negative (TurnLeft→TurnRight, SideStepLeft→SideStepRight),
+        // The Advance loop handles negative delta by checking against
-        // swap Low↔High so the advance loop counts DOWN from the swapped EndFrame
+        // StartFrame as the lower boundary. GetStartFramePosition uses
-        // toward the swapped StartFrame.  The pseudocode says:
+        // EndFrame (the HIGH value) to start the cursor near the top
-        //   if speedScale < 0: swap startFrame ↔ endFrame
+        // for reverse playback, so the cursor traverses all frames
-        if (fr < 0.0)
+        // from high→low instead of being stuck in [0,1).
-        {
+        if (low > high) high = low;
-            (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
-        }
 
         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:
+        // Without swap: StartFrame=0, EndFrame=3 (original range preserved).
-        //   StartFrame = 3 (was high), EndFrame = 0 (was low)
+        // GetStartFramePosition for negative speed = (EndFrame+1)-eps = (3+1)-eps ≈ 3.99999.
-        // GetStartFramePosition for negative speed = (EndFrame + 1) - EPSILON = (0+1) - eps ≈ 0.99999.
+        // The cursor starts near the HIGH end and counts DOWN toward StartFrame(=0).
-        // The cursor starts just below frame 1 and counts DOWN toward EndFrame(=0).
         double pos = GetFramePosition(seq);
-        Assert.True(pos > 0.9 && pos < 1.0,
+        Assert.True(pos > 3.9 && pos < 4.0,
-            $"Expected framePosition near 0.99999 (reverse start near EndFrame+1) but got {pos}");
+            $"Expected framePosition near 3.99999 (reverse start near EndFrame+1) but got {pos}");
     }
 
     [Fact]