feat(net+app): Phase B.3 — portal-space state machine for teleports

PlayerTeleport (0xF751) is a standalone GameMessage (u16 sequence,
align-4). When received, WorldSession fires TeleportStarted(uint sequence).

GameWindow subscribes: OnTeleportStarted sets PlayerMovementController.State
= PortalSpace, freezing all WASD/physics input. OnLivePositionUpdated
detects arrival (different landblock or >100 unit jump on our character guid),
recenters the streaming origin, resolves physics for ground Z, snaps the
player entity + controller, returns State to InWorld, and sends
GameActionLoginComplete directly (matching holtburger's PlayerTeleport
handler: send_login_complete on every portal transition).

PlayerMovementController gains PlayerState enum + early-return guard: if
State == PortalSpace, Update() returns a zero-movement result immediately
so no MoveToState / AutonomousPosition messages are emitted during transit.

WorldSession gains ResetLoginComplete() for callers that need to re-arm
the latch (documented; not called by the teleport path since we send
LoginComplete directly rather than through the PlayerCreate latch).

Opcode source: holtburger/crates/holtburger-protocol/src/opcodes.rs:84
Wire layout: holtburger/crates/.../movement/messages/teleport.rs

Build: 0 errors. Tests: 283 passed, 0 failed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/AcDream.Core.Net/WorldSession.cs

@@ -92,6 +92,26 @@ public sealed class WorldSession : IDisposable
     /// </summary>
     public event Action<EntityPositionUpdate>? PositionUpdated;
 
+    /// <summary>
+    /// Fires when the server sends a PlayerTeleport (0xF751) game message,
+    /// signalling that the player is entering portal space. The uint payload
+    /// is the teleport sequence number parsed from the message body (u16,
+    /// aligned to 4 bytes — per holtburger's teleport.rs wire layout).
+    /// Subscribers should freeze movement input until the destination
+    /// UpdatePosition arrives.
+    /// </summary>
+    public event Action<uint>? TeleportStarted;
+
+    /// <summary>
+    /// Allow re-sending LoginComplete after a portal teleport. The normal
+    /// _loginCompleteSent latch prevents duplicate sends on the initial spawn
+    /// path; this method resets it so the teleport completion path can send
+    /// another LoginComplete to tell the server the client has finished loading
+    /// the destination cell. Pattern from holtburger's PlayerTeleport handler
+    /// (client/messages.rs line 434-440: call send_login_complete on teleport).
+    /// </summary>
+    public void ResetLoginComplete() => _loginCompleteSent = false;
+
     /// <summary>Raised every time the state machine transitions.</summary>
     public event Action<State>? StateChanged;
 
@@ -426,6 +446,23 @@ public sealed class WorldSession : IDisposable
                         posUpdate.Value.Velocity));
                 }
             }
+            else if (op == 0xF751u)  // PlayerTeleport — server is moving us through a portal
+            {
+                // Phase B.3: holtburger opcodes.rs confirms 0xF751 is the
+                // PlayerTeleport standalone GameMessage (NOT wrapped in 0xF7B0).
+                // Wire layout (teleport.rs): u16 teleport_sequence, then
+                // aligned to 4 bytes. Per holtburger's client handler, the
+                // correct response is send_login_complete() at the destination.
+                // Here we fire TeleportStarted so GameWindow can freeze
+                // movement; the LoginComplete is sent from GameWindow once
+                // the destination UpdatePosition is received and the player
+                // has been snapped to the new cell.
+                uint sequence = 0;
+                if (body.Length >= 6)
+                    sequence = System.Buffers.Binary.BinaryPrimitives.ReadUInt16LittleEndian(
+                        body.AsSpan(4, 2));
+                TeleportStarted?.Invoke(sequence);
+            }
         }
     }