fix(G.3): recenter streaming onto the spawn landblock at login (#133)

A character saved inside a far dungeon hung at the #107 auto-entry hold because
the streaming center was fixed at the startup default and the login spawn never
recentered it, so the dungeon never streamed. Mirror the teleport-arrival
recenter on the login player-spawn path: when the player's spawn landblock
differs from the current center, recenter before translating the spawn position
(landblock-local -> new-center frame). No-op for a same-landblock (normal
Holtburg) login.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -2436,6 +2436,40 @@ public sealed class GameWindow : IDisposable
         // landblock; each neighbor landblock is offset by 192 units per step.
         int lbX = (int)((p.LandblockId >> 24) & 0xFFu);
         int lbY = (int)((p.LandblockId >> 16) & 0xFFu);
+
+        // G.3 (#133): recenter streaming onto the player's spawn landblock at
+        // login. The streaming center (_liveCenterX/_liveCenterY) is pinned to
+        // the startup default (Holtburg, 0xA9B4) and is otherwise only moved by
+        // the teleport-arrival path (OnLivePositionUpdated, ~line 4901). A
+        // character saved INSIDE a far dungeon spawns with that dungeon's
+        // landblock id, but the center never followed it, so the dungeon (tens
+        // of km away in world space) never streamed and the #107 auto-entry
+        // gate's SampleTerrainZ(pe.Position) waited forever — the player hung
+        // frozen at login. Mirror the teleport-arrival recenter HERE, for the
+        // PLAYER's spawn only, BEFORE the world-space translation below: when
+        // the spawn landblock differs from the current center, move the center
+        // onto it so the spawn maps to (PositionX, PositionY, PositionZ) in the
+        // new center frame (identical to the teleport path's
+        // `newWorldPos = new Vector3(p.PositionX, p.PositionY, p.PositionZ)`),
+        // and the next StreamingController.Tick observes the new center and
+        // streams the spawn landblock.
+        //
+        // No-op for a normal Holtburg login: the saved spawn landblock equals
+        // the default center, so the guard is false and origin/worldPos are
+        // byte-identical to the pre-fix path. Gated on the player guid so NPC /
+        // object spawns never move the center. Idempotent + thrash-free: a
+        // re-sent CreateObject for the same spawn landblock leaves the center
+        // already-equal, so the guard is false on every repeat.
+        if (spawn.Guid == _playerServerGuid
+            && (lbX != _liveCenterX || lbY != _liveCenterY))
+        {
+            Console.WriteLine(
+                $"live: login spawn — recentering streaming from ({_liveCenterX},{_liveCenterY}) " +
+                $"to ({lbX},{lbY}) for player spawn @0x{p.LandblockId:X8}");
+            _liveCenterX = lbX;
+            _liveCenterY = lbY;
+        }
+
         var origin = new System.Numerics.Vector3(
             (lbX - _liveCenterX) * 192f,
             (lbY - _liveCenterY) * 192f,