fix(app): Phase B.2 — use server position directly, fix yaw wrap + turn spam

Three more fixes from the diagnostic dump:

1. Initial position: PhysicsEngine.Resolve was mapping the player
   into an indoor EnvCell (foundry at Z=66) when they're standing
   on outdoor terrain at Z=93+. The cell-containment check was too
   aggressive for initial placement. Now uses the server-sent
   position directly — the server already gave us a valid position.

2. Yaw unbounded: mouse delta accumulated without wrapping, growing
   to 24+ radians. Now wraps to [-PI, PI] after every turn.

3. Turn command spam: MouseDeltaX > 0.5 threshold was too low for
   raw pixel deltas. Any mouse jitter triggered turnCmd flips every
   frame → stateChanged=True → MoveToState flood to the server.
   Mouse turning now only affects yaw directly; turn COMMANDS only
   come from A/D keyboard (matching retail client behavior where
   mouse-look doesn't generate a TurnRight/TurnLeft command).

265 tests still green.

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

src/AcDream.App/Input/PlayerMovementController.cs

@@ -79,6 +79,10 @@ public sealed class PlayerMovementController
         if (input.TurnLeft)
             Yaw += TurnSpeed * dt;
         Yaw -= input.MouseDeltaX * MouseTurnSensitivity;
+        // Wrap yaw to [-PI, PI] so it doesn't grow unbounded and cause
+        // NaN/overflow in sin/cos and confuse the chase camera offset.
+        while (Yaw > MathF.PI) Yaw -= 2f * MathF.PI;
+        while (Yaw < -MathF.PI) Yaw += 2f * MathF.PI;
 
         // 2. Compute movement delta in the player's facing direction.
         float speed = input.Run ? RunSpeed : WalkSpeed;
@@ -130,12 +134,17 @@ public sealed class PlayerMovementController
             sidestepSpeed = speed * 0.5f / WalkSpeed;
         }
 
-        if (input.TurnRight || input.MouseDeltaX > 0.5f)
+        // Turn commands from KEYBOARD only (A/D). Mouse turning is applied
+        // directly to Yaw above and doesn't generate a turn command — if it
+        // did, mouse jitter would flip turnCmd between TurnRight/TurnLeft
+        // every frame, causing stateChanged=True on every frame and flooding
+        // the server with MoveToState spam.
+        if (input.TurnRight)
         {
             turnCmd = 0x6500000Du;  // TurnRight
             turnSpeed = TurnSpeed;
         }
-        else if (input.TurnLeft || input.MouseDeltaX < -0.5f)
+        else if (input.TurnLeft)
         {
             turnCmd = 0x6500000Eu;  // TurnLeft
             turnSpeed = TurnSpeed;

src/AcDream.App/Rendering/GameWindow.cs

@@ -203,12 +203,15 @@ public sealed class GameWindow : IDisposable
                             float plocalX = playerEntity.Position.X - (plbX - _liveCenterX) * 192f;
                             float plocalY = playerEntity.Position.Y - (plbY - _liveCenterY) * 192f;
                             uint pinitCellId = ((uint)plbX << 24) | ((uint)plbY << 16) | 0x0001u;
-                            // Let the physics engine resolve the correct Z for the initial position
+                            // Use the server-sent position directly — the server already
-                            // so we don't start underground.
+                            // gave us a valid position at CreateObject time. Running it
-                            var initResult = _physicsEngine.Resolve(
+                            // through PhysicsEngine.Resolve was mapping the player into
-                                playerEntity.Position, pinitCellId,
+                            // an indoor cell (e.g., the foundry at Z=66) when they're
-                                System.Numerics.Vector3.Zero, 10f);
+                            // actually standing on outdoor terrain at Z=93+. The physics
-                            _playerController.SetPosition(initResult.Position, initResult.CellId);
+                            // engine's cell-containment check is too aggressive for the
+                            // initial placement. Once the player starts moving, Resolve
+                            // will keep them on the correct surface.
+                            _playerController.SetPosition(playerEntity.Position, pinitCellId & 0xFFFFu);
                             // Derive initial yaw from the entity's server-sent rotation
                             // rather than hardcoding. Extract yaw from the quaternion.
                             var q = playerEntity.Rotation;
@@ -216,6 +219,12 @@ public sealed class GameWindow : IDisposable
                                 2f * (q.W * q.Z + q.X * q.Y),
                                 1f - 2f * (q.Y * q.Y + q.Z * q.Z));
                             _playerController.Yaw = yaw;
+
+                            Console.WriteLine($"[PLAYER-INIT] entityPos=({playerEntity.Position.X:F1},{playerEntity.Position.Y:F1},{playerEntity.Position.Z:F1}) " +
+                                              $"entityRot=({q.X:F3},{q.Y:F3},{q.Z:F3},{q.W:F3}) " +
+                                              $"initCellId=0x{(pinitCellId & 0xFFFFu):X4} " +
+                                              $"yaw={yaw:F3} " +
+                                              $"physics landblocks={_physicsEngine.LandblockCount}");
                             _chaseCamera = new AcDream.App.Rendering.ChaseCamera
                             {
                                 Aspect = _window!.Size.X / (float)_window.Size.Y,
@@ -1489,6 +1498,16 @@ public sealed class GameWindow : IDisposable
 
             var result = _playerController.Update((float)dt, input);
 
+            // DIAG: dump player state every ~60 frames to see what's happening.
+            if (_perfFrameCount % 60 == 0)
+            {
+                Console.WriteLine($"[PLAYER] pos=({result.Position.X:F1},{result.Position.Y:F1},{result.Position.Z:F1}) " +
+                                  $"cell=0x{result.CellId:X8} ground={result.IsOnGround} " +
+                                  $"yaw={_playerController.Yaw:F2} " +
+                                  $"fwdCmd={result.ForwardCommand?.ToString("X8") ?? "idle"} " +
+                                  $"stateChanged={result.MotionStateChanged}");
+            }
+
             // Update the player entity's position + rotation so it renders at
             // the physics-resolved location each frame.
             if (_entitiesByServerGuid.TryGetValue(_playerServerGuid, out var pe))

src/AcDream.Core/Physics/PhysicsEngine.cs

@@ -21,6 +21,9 @@ public sealed class PhysicsEngine
 {
     private readonly Dictionary<uint, LandblockPhysics> _landblocks = new();
 
+    /// <summary>Number of registered landblocks (diagnostic).</summary>
+    public int LandblockCount => _landblocks.Count;
+
     private sealed record LandblockPhysics(
         TerrainSurface Terrain,
         IReadOnlyList<CellSurface> Cells,