fix: complete retail parity stability pass

src/AcDream.Core/Physics/PhysicsTimestampGate.cs

@@ -192,11 +192,12 @@ public sealed class PhysicsTimestampGate
             _timestamps[ForcePosition] = forcePosition;
 
             // SmartBox::HandleReceivedPosition 0x00453FD0: a fresh local
-            // FORCE_POSITION whose teleport is exactly equal blips immediately,
-            // assigns POSITION_TS directly (even equal/older), preserves the
-            // current heading, sends a position event, and returns WITHOUT
-            // advancing TELEPORT_TS.
-            if (teleport == _timestamps[Teleport])
+            // FORCE_POSITION whose teleport stamp is not older (equal OR
+            // newer) blips immediately, assigns POSITION_TS directly (even
+            // equal/older), preserves the current heading, sends a position
+            // event, and returns WITHOUT advancing TELEPORT_TS. The same
+            // wrap-safe predicate is used by IsFreshTeleportStart above.
+            if (!IsNewer(teleport, _timestamps[Teleport]))
             {
                 _timestamps[Position] = position;
                 return PositionTimestampDisposition.ForcePosition;

src/AcDream.Core/Physics/RetailAnimationCyclePlayback.cs

@@ -16,26 +16,13 @@ namespace AcDream.Core.Physics;
 /// transitional blending.
 ///
 /// <para>
-/// This exact advance-with-wrap-then-lerp/slerp algorithm already exists as
-/// an inline, App-layer-only implementation for the "legacy" (no
-/// <see cref="AnimationSequencer"/>) NPC idle-cycle path —
-/// <c>LiveEntityAnimationPresenter.Present</c>'s non-sequencer branch
-/// (<c>CurrFrame += legacyAdvanceSeconds * Framerate</c> with the same
-/// modulo wrap) and its private <c>TryResolvePartFrame</c> helper (the same
-/// frame-bracket lerp/slerp). That call site has a live entity, a
+/// This is the shared implementation used by both the "legacy" (no
+/// <see cref="AnimationSequencer"/>) NPC idle-cycle path and the chargen
+/// preview. The live presenter has a live entity, a
 /// <c>LiveEntityRuntime</c> membership, and per-tick elapsed time supplied by
 /// the render loop; the chargen preview has none of that (there is no live
-/// entity — character creation hasn't happened yet), so it cannot reuse that
-/// class directly. Rather than re-typing the same formula a second time,
-/// this Core, pure, unit-testable class is the shared primitive: the
-/// chargen preview (<c>AcDream.App.Rendering.ChargenPreviewAnimator</c>)
-/// consumes it directly, and it is safe for a future pass to redirect
-/// <c>LiveEntityAnimationPresenter</c>'s inline copy through it as a
-/// behavior-preserving mechanical follow-up (not done here — that file is
-/// live, heavily tested production entity-rendering code with zero relation
-/// to this preview-only feature, so touching it is out of this slice's
-/// blast radius by design, not oversight). Tracked as
-/// <c>docs/ISSUES.md</c> #403 so the follow-up has an owner.
+/// entity — character creation hasn't happened yet), so neither consumer can
+/// own the primitive. Keeping it here prevents the two paths from drifting.
 /// </para>
 /// </summary>
 public static class RetailAnimationCyclePlayback
@@ -43,14 +30,15 @@ public static class RetailAnimationCyclePlayback
     /// <summary>
     /// Advances <paramref name="currFrame"/> by <c>elapsedSeconds * framerate</c>
     /// and wraps it back into <c>[lowFrame, highFrame]</c> with the SAME modulo
-    /// shape <c>LiveEntityAnimationPresenter.Present</c>'s legacy branch uses
+    /// shape retail playback and the live presenter's legacy branch use
     /// (<c>over % (span + 1)</c>, not a plain clamp — a frame position that
     /// overshoots the end by more than one span wraps around more than once
     /// rather than sticking at the boundary, matching a long stall/resume).
     /// Returns <paramref name="currFrame"/> unchanged for a degenerate cycle
-    /// (<paramref name="highFrame"/> &lt;= <paramref name="lowFrame"/>), a
-    /// non-positive <paramref name="framerate"/>, or a non-positive
-    /// <paramref name="elapsedSeconds"/>.
+    /// (<paramref name="highFrame"/> &lt;= <paramref name="lowFrame"/>) or a
+    /// non-positive <paramref name="elapsedSeconds"/>. A negative framerate
+    /// advances backward and clamps at the low frame, matching the former
+    /// live-presenter implementation exactly.
     /// </summary>
     public static float Advance(
         float currFrame,
@@ -60,7 +48,7 @@ public static class RetailAnimationCyclePlayback
         float elapsedSeconds)
     {
         int span = highFrame - lowFrame;
-        if (span <= 0 || framerate <= 0f || elapsedSeconds <= 0f)
+        if (span <= 0 || elapsedSeconds <= 0f)
             return currFrame;
 
         float next = currFrame + elapsedSeconds * framerate;
@@ -84,8 +72,7 @@ public static class RetailAnimationCyclePlayback
     /// back to <paramref name="lowFrame"/>). Returns <c>false</c> — with
     /// <c>default</c> outputs — when <paramref name="partIndex"/> is outside
     /// the bracketing frame's part list, matching
-    /// <c>LiveEntityAnimationPresenter.TryResolvePartFrame</c>'s no-
-    /// sequence-frames branch exactly.
+    /// the live presenter's no-sequence-frames branch exactly.
     /// </summary>
     public static bool TryInterpolatePart(
         Animation animation,