fix(G.3): register portals-only connector cells for visibility (#133 ramp grey)

The grey "barrier" at a dungeon ramp was a one-cell registration gap. The ramp's
connector cell (0x0007014D) is a portals-only pass-through — CellMesh.Build yields
0 drawable sub-meshes for it (you walk through it on adjacent floors). But the whole
registration block — including the portal-VISIBILITY registration (BuildLoadedCell ->
_cellVisibility) — was gated behind `if (cellSubMeshes.Count > 0)`. So that cell was
never added to the visibility graph; the flood lookup-missed it (PortalVisibilityBuilder
:369), couldn't traverse it to the room below, and the grey clear color showed through.

Confirmed live via two added probes: [cellreg] registered=204/205 (only 0x014D missing)
+ [pv-trace] p4->0x0007014D skip=lookup-miss. After the fix: registered=205,
hasRamp=True, skip=lookup-miss gone, the room below renders.

Fix: compute the cell transforms and call BuildLoadedCell (visibility) for EVERY cell
with a valid cellStruct, regardless of drawable sub-meshes — matching retail, which
keeps the whole landblock cell array resident before the flood runs. Drawing
(RegisterCell, _pendingCellMeshes) and the physics BSP (CacheCellStruct) stay gated on
drawable geometry (a portals-only connector has nothing to draw and no collision
surface). Not a regression from the FPS-collapse work — a pre-existing gate the
now-navigable dungeon exposed (every ramp/stair/cellar mouth would show it).

TEMP diagnostics retained for the residual angle-grey investigation (strip after):
[cellreg] (GameWindow), the 0x0007 [pv-trace] gate widen + raw-NDC bbox (PortalVisibility-
Builder). Three earlier render-math theories (portal_side, on-screen clip, near-eye
projection) were each refuted by apparatus/probe before shipping — this is the verified one.

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

src/AcDream.App/Rendering/GameWindow.cs

@@ -61,6 +61,7 @@ public sealed class GameWindow : IDisposable
     // though the title-bar FPS is only updated every 0.5s.
     private double _lastFps = 60.0;
     private double _lastFrameMs = 16.7;
+    private string _lastCellRegSig = "";   // TEMP #133 ramp-flood-collapse [cellreg] dedup
 
     // Phase I.2: per-frame counters surfaced through the ImGui DebugPanel
     // VM closures. Computed once per render pass alongside the frustum
@@ -5664,16 +5665,12 @@ public sealed class GameWindow : IDisposable
                     // Static objects inside the cell continue to flow through the dispatcher
                     // as WorldEntity records below — they have real GfxObj MeshRefs that work
                     // fine; EnvCellRenderer.RegisterCell receives an empty staticObjects list.
-                    var cellSubMeshes = AcDream.Core.Meshing.CellMesh.Build(envCell, cellStruct, _dats);
+                    // Transforms — needed by the portal-visibility cell (unlifted) AND the
-                    if (cellSubMeshes.Count > 0)
+                    // render/physics path. Computed for EVERY cell with a valid cellStruct,
-                    {
+                    // not just drawable ones. Keep the small render lift out of physics; retail
-                        _pendingCellMeshes[envCellId] = cellSubMeshes;
+                    // BSP contact planes use the EnvCell origin verbatim. The lift constant is
-
+                    // shared with every draw-space consumer of portal polygons (OutsideView
-                        // Keep the small render lift out of physics; retail BSP
+                    // gate, seal/punch fans) — PortalVisibilityBuilder.ShellDrawLiftZ (#130).
-                        // contact planes use the EnvCell origin verbatim. The lift
-                        // constant is shared with every draw-space consumer of
-                        // portal polygons (OutsideView gate, seal/punch fans) —
-                        // see PortalVisibilityBuilder.ShellDrawLiftZ (#130).
                     var physicsCellOrigin = envCell.Position.Origin + lbOffset;
                     var cellOrigin = physicsCellOrigin + new System.Numerics.Vector3(
                         0f, 0f, AcDream.App.Rendering.PortalVisibilityBuilder.ShellDrawLiftZ);
@@ -5684,6 +5681,26 @@ public sealed class GameWindow : IDisposable
                         System.Numerics.Matrix4x4.CreateFromQuaternion(envCell.Position.Orientation) *
                         System.Numerics.Matrix4x4.CreateTranslation(physicsCellOrigin);
 
+                    // PORTAL VISIBILITY: register EVERY cell with a valid cellStruct, regardless
+                    // of whether CellMesh.Build produced drawable sub-meshes. A portals-only
+                    // pass-through connector (a ramp / stair / cellar mouth) yields 0 render
+                    // sub-meshes but MUST be in the visibility graph so the flood can traverse it
+                    // to the cells beyond — otherwise the flood lookup-misses the unregistered
+                    // neighbour and the grey clear shows through the opening (#133: ramp
+                    // neighbour 0x0007014D had 0 sub-meshes → unregistered → vis=1 grey barrier
+                    // at the ramp; confirmed via [cellreg] registered=204/205 + [pv-trace]
+                    // skip=lookup-miss). Retail keeps the whole landblock cell array resident
+                    // before the flood runs; BuildLoadedCell reads the cellStruct portals, NOT
+                    // the render sub-meshes. The +0.02 m render lift is a DRAW concern only and
+                    // is intentionally NOT fed into the visibility transform (#119-residual: the
+                    // lift shifted horizontal portal planes 2 cm, side-culling deck/stair cells).
+                    BuildLoadedCell(envCellId, envCell, cellStruct, physicsCellOrigin, physicsCellTransform);
+
+                    var cellSubMeshes = AcDream.Core.Meshing.CellMesh.Build(envCell, cellStruct, _dats);
+                    if (cellSubMeshes.Count > 0)
+                    {
+                        _pendingCellMeshes[envCellId] = cellSubMeshes;
+
                         // Phase A8: register the cell with EnvCellRenderer for rendering.
                         // staticObjects is empty — cell stabs continue as separate WorldEntity
                         // records via the dispatcher (see lines below for the unchanged stab path).
@@ -5697,23 +5714,8 @@ public sealed class GameWindow : IDisposable
                             cellRotation:      envCell.Position.Orientation,
                             staticObjects:     System.Array.Empty<(uint, System.Numerics.Vector3, System.Numerics.Quaternion, bool, System.Numerics.Matrix4x4)>());
 
-                        // Step 4: build LoadedCell for portal visibility — with the
+                        // Cache CellStruct physics BSP for indoor collision (UNCHANGED — gated
-                        // PHYSICS (unlifted) transform. The +0.02 m render lift above
+                        // on drawable cells; a portals-only connector has no collision surface).
-                        // is a DRAW concern (shell z-fighting vs terrain); feeding it
-                        // into the visibility graph shifted every HORIZONTAL portal
-                        // plane 2 cm up, putting an eye standing on a deck/landing
-                        // 10–20 mm BELOW the lifted plane — outside the side test's
-                        // ±10 mm in-plane window — so the cell behind the portal was
-                        // side-culled: the tower-top staircase vanish + roof flap
-                        // (#119-residual; captured live at eye z=126.803 vs the
-                        // 010A→0107 plane at 126.80, reproduced ONLY with the lift in
-                        // TowerAscentReplayTests.CapturedTopOfStairs_*). Vertical
-                        // doorways were immune (the lift slides their planes along
-                        // themselves), which is why this hit exactly stairs, decks,
-                        // and cellar mouths.
-                        BuildLoadedCell(envCellId, envCell, cellStruct, physicsCellOrigin, physicsCellTransform);
-
-                        // Cache CellStruct physics BSP for indoor collision (UNCHANGED).
                         _physicsDataCache.CacheCellStruct(envCellId, envCell, cellStruct, physicsCellTransform);
                     }
                 }
@@ -7689,6 +7691,25 @@ public sealed class GameWindow : IDisposable
                 playerCellId:      playerRoot?.CellId ?? 0u,
                 lights:            Lighting);
 
+            // TEMP (#133 ramp-flood-collapse): cell-registration completeness for the
+            // player's dungeon landblock. If the ramp neighbour (0x....014D in 0x0007)
+            // is absent from _cellVisibility, the portal flood can't admit it (lookup-miss
+            // at PortalVisibilityBuilder.cs:369) and the grey clear shows through. Logs only
+            // when the count or ramp-presence changes (dedup) — pairs with [pv-trace] skip=.
+            if (AcDream.Core.Rendering.RenderingDiagnostics.ProbeFlapEnabled && playerRoot is not null)
+            {
+                uint plb = playerRoot.CellId >> 16;
+                int reg = _cellVisibility.GetCellsForLandblock(plb).Count;
+                uint rampId = (plb << 16) | 0x014Du;
+                bool hasRamp = _cellVisibility.TryGetCell(rampId, out _);
+                string sig = plb.ToString("X4") + ":" + reg + ":" + hasRamp;
+                if (sig != _lastCellRegSig)
+                {
+                    _lastCellRegSig = sig;
+                    Console.WriteLine($"[cellreg] lb=0x{plb:X4} registered={reg} hasRamp0x{rampId:X8}={hasRamp} playerCell=0x{playerRoot.CellId:X8}");
+                }
+            }
+
             // Never cull the landblock the player is currently on.
             uint? playerLb = null;
             if (_playerMode && _playerController is not null)

src/AcDream.App/Rendering/PortalVisibilityBuilder.cs

@@ -759,7 +759,13 @@ public static class PortalVisibilityBuilder
 
     private static bool IsHoltburgIndoorProbeCell(uint cellId)
     {
-        if ((cellId & 0xFFFF0000u) != 0xA9B40000u)
+        uint lb = cellId & 0xFFFF0000u;
+        // TEMP (#133 ramp-flood-collapse diagnosis): widen the [pv-trace] gate to the
+        // 0x0007 Town Network dungeon so the per-portal skip= reason (lookup-miss /
+        // clip-empty / reciprocal-empty / side) is emitted for the ramp neighbour.
+        if (lb == 0x00070000u)
+            return true;
+        if (lb != 0xA9B40000u)
             return false;
         uint low = cellId & 0xFFFFu;
         return low >= 0x016F && low <= 0x0175;
@@ -821,6 +827,7 @@ public static class PortalVisibilityBuilder
             // genuinely off-screen; the ndc coords (post-clip, bounded) show where on screen it lands.
             int projN = -1, clipN = -1;
             string ndcText = "";
+            string rawText = "";
             if (i < cameraCell.PortalPolygons.Count)
             {
                 var poly = cameraCell.PortalPolygons[i];
@@ -830,6 +837,21 @@ public static class PortalVisibilityBuilder
                     projN = clip.Length;
                     if (clip.Length >= 3)
                     {
+                        // Raw projected-NDC bbox (pre-screen-clip): WHERE the portal lands on screen,
+                        // even when ClipToRegion drops it to empty. A clip=0 portal whose raw bbox is
+                        // inside [-1,1] is on-screen-but-wrongly-dropped (the bug); a bbox outside
+                        // [-1,1] is genuinely off-screen (correct). Distinguishes the two.
+                        float rminX = float.MaxValue, rminY = float.MaxValue, rmaxX = -float.MaxValue, rmaxY = -float.MaxValue;
+                        foreach (var cv in clip)
+                        {
+                            if (cv.W <= 1e-6f) continue;
+                            float nx = cv.X / cv.W, ny = cv.Y / cv.W;
+                            rminX = MathF.Min(rminX, nx); rmaxX = MathF.Max(rmaxX, nx);
+                            rminY = MathF.Min(rminY, ny); rmaxY = MathF.Max(rmaxY, ny);
+                        }
+                        if (rminX <= rmaxX)
+                            rawText = FormattableString.Invariant($" raw=[{rminX:F1},{rminY:F1}..{rmaxX:F1},{rmaxY:F1}]");
+
                         var ndc = PortalProjection.ClipToRegion(clip, FullScreenQuad);
                         clipN = ndc.Length;
                         var ns = new System.Text.StringBuilder(48);
@@ -842,6 +864,7 @@ public static class PortalVisibilityBuilder
             sb.Append(" D=").Append(float.IsNaN(d) ? "na" : d.ToString("F2"));
             sb.Append(side ? " TRV" : " CULL");
             sb.Append(" proj=").Append(projN).Append(" clip=").Append(clipN);
+            if (rawText.Length > 0) sb.Append(rawText);
             if (ndcText.Length > 0) sb.Append(" ndc=").Append(ndcText);
         }
         sb.Append(" || outPolys=").Append(frame.OutsideView.Polygons.Count);