fix(A.5 T13-T16): canonicalize ids; init-only radii; demote/promote tests

Code review on T13-T16 bundle (commits fb10c3f/aff35d2/b8d80fe/c4fd373/31d312a)
flagged 3 Important + 2 test-coverage gaps. Apply all 5:

Important #1: GpuWorldState.AddEntitiesToExistingLandblock didn't
canonicalize landblockId. Streaming callers always pass canonical
0xAAAA0xFFFF ids, but the public API silently key-missed for callers
that mirror AppendLiveEntity's cell-resolved-id pattern. Both new
methods now canonicalize the id on entry.

Important #2: RemoveEntitiesFromLandblock asymmetry with RemoveLandblock
re: persistent-entity rescue. Documented as intentional — demote-tier
entities are atlas-tier only (procedural scenery, dat-static stabs/
buildings; never ServerGuid != 0); the local player and live server
spawns live in their LB via RelocateEntity per frame and aren't
affected by atlas-layer demote.

Important #3: StreamingController.NearRadius / FarRadius were { get; set; }
but mutating them after the first Tick is a no-op (StreamingRegion
snapshots the values). Switched to { get; } only with XML doc warning.

Test gap #1: ToDemote routing through Tick — added test that walks
the player past hysteresis and asserts entities drop while terrain
stays.

Test gap #2: Promoted result routing through Tick — added test that
enqueues a Promoted and asserts AddEntitiesToExistingLandblock fires.

Deferred Minor: dead _streamingRadius write + style consistency on
fully-qualified IReadOnlyList — non-load-bearing, can roll into a later
cleanup.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Streaming/GpuWorldState.cs

@@ -343,14 +343,29 @@ public sealed class GpuWorldState
     /// Drop all entities from a landblock without removing the terrain. Used
     /// by two-tier streaming when a landblock crosses Near→Far hysteresis.
     /// Per Phase A.5 spec §4.4.
+    ///
+    /// <para>
+    /// <b>Persistent-entity rescue is intentionally omitted</b> (unlike
+    /// <see cref="RemoveLandblock"/>): demote-tier entities are atlas-tier
+    /// only (procedural scenery, dat-static stabs/buildings) — they never
+    /// have <c>ServerGuid != 0</c> and so can never be in <see cref="_persistentGuids"/>.
+    /// The local player and other live server-spawned entities live in their
+    /// landblock via <c>RelocateEntity</c> per frame and are not affected
+    /// by Near→Far demotion of dat-static landblock layers.
+    /// </para>
     /// </summary>
     public void RemoveEntitiesFromLandblock(uint landblockId)
     {
-        if (!_loaded.TryGetValue(landblockId, out var lb)) return;
+        // A.5 T14 follow-up: canonicalize for symmetry with AppendLiveEntity.
+        // Streaming callers always pass canonical (0xAAAA0xFFFF) ids; this
+        // protects against future callers that mirror AppendLiveEntity's
+        // cell-resolved-id pattern.
+        uint canonical = (landblockId & 0xFFFF0000u) | 0xFFFFu;
+        if (!_loaded.TryGetValue(canonical, out var lb)) return;
         if (_wbSpawnAdapter is not null)
-            _wbSpawnAdapter.OnLandblockUnloaded(landblockId);
-        _loaded[landblockId] = new LoadedLandblock(lb.LandblockId, lb.Heightmap, System.Array.Empty<WorldEntity>());
-        _pendingByLandblock.Remove(landblockId);
+            _wbSpawnAdapter.OnLandblockUnloaded(canonical);
+        _loaded[canonical] = new LoadedLandblock(lb.LandblockId, lb.Heightmap, System.Array.Empty<WorldEntity>());
+        _pendingByLandblock.Remove(canonical);
         RebuildFlatView();
     }
 
@@ -361,16 +376,23 @@ public sealed class GpuWorldState
     /// landblock isn't loaded yet (handles the rare "promote arrives before
     /// far load completes" race).
     /// Per Phase A.5 spec §4.4.
+    ///
+    /// <para>
+    /// <b>Landblock id is canonicalized</b> (low 16 bits forced to 0xFFFF) —
+    /// callers may pass cell-resolved ids and they will key correctly.
+    /// </para>
     /// </summary>
-    public void AddEntitiesToExistingLandblock(uint landblockId, System.Collections.Generic.IReadOnlyList<WorldEntity> entities)
+    public void AddEntitiesToExistingLandblock(uint landblockId, IReadOnlyList<WorldEntity> entities)
     {
-        if (!_loaded.TryGetValue(landblockId, out var lb))
+        // A.5 T14 follow-up: canonicalize for symmetry with AppendLiveEntity.
+        uint canonical = (landblockId & 0xFFFF0000u) | 0xFFFFu;
+        if (!_loaded.TryGetValue(canonical, out var lb))
         {
             // Park as pending — same pattern as AppendLiveEntity for not-yet-loaded LBs.
-            if (!_pendingByLandblock.TryGetValue(landblockId, out var bucket))
+            if (!_pendingByLandblock.TryGetValue(canonical, out var bucket))
             {
                 bucket = new List<WorldEntity>();
-                _pendingByLandblock[landblockId] = bucket;
+                _pendingByLandblock[canonical] = bucket;
             }
             bucket.AddRange(entities);
             return;
@@ -378,9 +400,9 @@ public sealed class GpuWorldState
         var merged = new List<WorldEntity>(lb.Entities.Count + entities.Count);
         merged.AddRange(lb.Entities);
         merged.AddRange(entities);
-        _loaded[landblockId] = new LoadedLandblock(lb.LandblockId, lb.Heightmap, merged);
+        _loaded[canonical] = new LoadedLandblock(lb.LandblockId, lb.Heightmap, merged);
         if (_wbSpawnAdapter is not null)
-            _wbSpawnAdapter.OnLandblockLoaded(_loaded[landblockId]);
+            _wbSpawnAdapter.OnLandblockLoaded(_loaded[canonical]);
         RebuildFlatView();
     }
 

src/AcDream.App/Streaming/StreamingController.cs

@@ -25,8 +25,25 @@ public sealed class StreamingController
     private readonly GpuWorldState _state;
     private StreamingRegion? _region;
 
-    public int NearRadius { get; set; }
-    public int FarRadius  { get; set; }
+    /// <summary>
+    /// Near-tier radius (LBs from observer that load full detail: terrain +
+    /// scenery + entities). Set at construction; readable thereafter.
+    /// </summary>
+    /// <remarks>
+    /// Mutating after the first <see cref="Tick"/> has no effect — the
+    /// internal <see cref="StreamingRegion"/> snapshots both radii on its
+    /// constructor. Treat as init-only post-Tick.
+    /// </remarks>
+    public int NearRadius { get; }
+
+    /// <summary>
+    /// Far-tier radius (LBs from observer that load terrain only). Set at
+    /// construction; readable thereafter.
+    /// </summary>
+    /// <remarks>
+    /// Mutating after the first <see cref="Tick"/> has no effect — see <see cref="NearRadius"/>.
+    /// </remarks>
+    public int FarRadius { get; }
 
     /// <summary>
     /// Cap on completions drained per <see cref="Tick"/> call. The cap is