feat(A7.L1): scope the point-light pool by last frame's visible cells (#79/#93/#176/#177)

The Town Network hub (498 registered fixtures) starved the player's own
room: BuildPointLightSnapshot's player-nearest-128 cap sorts by raw
Euclidean distance, which isn't a reliable proxy for "same room" in a
dense maze — a fixture on the other side of a wall can be geometrically
closer than the room's own torches and win the cap. LightSource.CellId
tagging and the [indoor-light] membership probe already existed from the
c500912b/#176 arc; the missing piece was a candidacy filter.

BuildPointLightSnapshot(playerWorldPos, visibleCells) now narrows
candidates to the frame's actual visible cells before the existing
dynamics-first player-nearest cap runs (cell-less lights, e.g. the viewer
fill, always included). GameWindow feeds LAST FRAME's already-rendered
RetailPViewFrameResult.DrawableCells — one frame of latency instead of
re-threading a mid-DrawInside callback, which was the exact mechanism
(c500912b) that caused the earlier #176 seam-floor flicker regression.
The distance-sort anchor stays the player, unchanged.

AP-85 updated in place (third revision) rather than adding a new row —
same underlying divergence, now with the render-visibility approximation
of retail's true DBObj-load/flush-bounded resident registry documented
alongside its residual risk (one unscoped frame on portal re-entry).

Core 2652+2skip / App 741+2skip / UI 425 / Net 385 green. Pending: user
visual gate at the Town Network fountain, and a #176 corridor-seam
non-regression recheck (Facility Hub, different landblock).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -794,6 +794,22 @@ public sealed class GameWindow : IDisposable
         new AcDream.Core.World.WorldTimeService(
             AcDream.Core.World.SkyStateProvider.Default());
     public readonly AcDream.Core.Lighting.LightManager Lighting = new();
+
+    // A7.L1 (2026-07-09) — last frame's rendered visible-cell set, fed into next
+    // frame's Lighting.BuildPointLightSnapshot scoping. One frame of latency
+    // (~16 ms) instead of a mid-DrawInside callback: DrawableCells only becomes
+    // known partway through DrawInside (after the flood + look-in merge), and the
+    // #176 correction already showed that rebuilding the light pool FROM a
+    // freshly-recomputed frame flood (the deleted RebuildScopedLights callback,
+    // c500912b) is a flicker mechanism. Reusing last frame's already-drawn set
+    // (MP-Alloc: reused HashSet, no per-frame alloc) decouples the light-scoping
+    // change from DrawInside's internals entirely. _lightPoolVisibleCellsValid is
+    // false until the first indoor frame completes, and is cleared on any
+    // outdoor-only frame so scoping fails open (unscoped) for one frame on
+    // re-entry rather than filtering by a stale dungeon's cell ids.
+    private readonly HashSet<uint> _lightPoolVisibleCells = new();
+    private bool _lightPoolVisibleCellsValid;
+
     public readonly AcDream.Core.World.WeatherSystem Weather = new();
     // Wired into the hook router in OnLoad so SetLightHook fires
     // from the animation pipeline flip the matching LightSource.IsLit.
@@ -9255,7 +9271,13 @@ public sealed class GameWindow : IDisposable
             // collected from ALL registered (=resident-cell) lights — it is a
             // function of player position only, so camera rotation cannot change
             // it. playerViewPos carries retail's no-player fallback (camPos).
-            Lighting.BuildPointLightSnapshot(playerViewPos);
+            // A7.L1: candidacy is additionally scoped to last frame's rendered
+            // visible-cell set (see _lightPoolVisibleCells) when available — the
+            // Town Network starvation fix. Unscoped (null) until the first indoor
+            // frame completes or after any outdoor-only frame.
+            Lighting.BuildPointLightSnapshot(
+                playerViewPos,
+                _lightPoolVisibleCellsValid ? _lightPoolVisibleCells : null);
             _wbDrawDispatcher?.SetSceneLights(Lighting.PointSnapshot);
             _envCellRenderer?.SetPointSnapshot(Lighting.PointSnapshot);   // A7 Fix D (D-2)
 
@@ -9682,6 +9704,14 @@ public sealed class GameWindow : IDisposable
                 envCellShellFilter = pviewResult.DrawableCells;
                 _interiorPartition = pviewResult.Partition;
 
+                // A7.L1: snapshot this frame's drawn cell set for NEXT frame's light-
+                // pool scoping. DrawableCells is the renderer's own reused scratch set
+                // (cleared/rebuilt every DrawInside call) — copy it, don't hold a
+                // reference to it.
+                _lightPoolVisibleCells.Clear();
+                _lightPoolVisibleCells.UnionWith(pviewResult.DrawableCells);
+                _lightPoolVisibleCellsValid = true;
+
                 // Flap root-cause apparatus (2026-06-07): per-frame, the EXACT Build inputs at 6 dp +
                 // the resulting flood count. The live flap shows flood flipping 2↔6 at an eye/player
                 // identical to cm; this answers whether the inputs differ sub-cm (jitter) or are
@@ -9742,6 +9772,10 @@ public sealed class GameWindow : IDisposable
                     neverCullLandblockId: playerLb,
                     visibleCellIds: null,
                     animatedEntityIds: animatedIds);
+
+                // A7.L1: no indoor draw this frame — fail open (unscoped) rather than
+                // scoping next frame's light pool by a stale dungeon's cell ids.
+                _lightPoolVisibleCellsValid = false;
             }
 
             // Phase U.3: close the world-geometry clip bracket opened above. From here down the