BR-2 task 1: phantom-site probe (ACDREAM_PROBE_PHANTOM)

The BR-1 pre-check left the #113 phantom residual with two surviving
suspects, both cell-side: (a) flood-admitted cells whose shell draws with
a pass-all slice (NoClipSlice fallback when the assembler handed no slot,
or an assembler slot-0 scissor-fallback slice), and (b) cell entity
buckets drawn unclipped + un-viewcone'd by design.

[phantom-shell]: per shell-pass cell, print-on-change - clip-enable
state, slot presence, every drawn slice's slot + plane count with
PASS-ALL flagged. [phantom-objs]: per object-list cell, print-on-change
- entity bucket size. Env-gated ACDREAM_PROBE_PHANTOM=1, zero cost off,
throwaway (strip when the phantom closes).

Repro protocol: launch with the probe on, stand at the hall bisect spot
(world ~216,-108 looking at the AAB3 meeting hall west face) where the
phantom is visible, read which mechanism fires for stair cells
0xAAB30100..0x106. Shells pass-all -> BR-2/BR-3 close it; statics ->
BR-5 closes it.

Build green; App suite green.

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

src/AcDream.App/Rendering/RetailPViewRenderer.cs

@@ -385,7 +385,15 @@ public sealed class RetailPViewRenderer
             _oneCell.Clear();
             _oneCell.Add(cellId);
 
-            foreach (var slice in GetCellSlicesOrNoClip(clipAssembly, cellId))
+            var slices = GetCellSlicesOrNoClip(clipAssembly, cellId);
+
+            // BR-2 phantom-site probe: which cells draw their shell with a
+            // pass-all slice (NoClipSlice fallback or assembler slot-0)?
+            if (AcDream.Core.Rendering.RenderingDiagnostics.ProbePhantomEnabled)
+                EmitPhantomShellProbe(cellId, slices, clipShells,
+                    hadSlot: clipAssembly.CellIdToViewSlices.ContainsKey(cellId));
+
+            foreach (var slice in slices)
             {
                 UseShellClipRouting(cellId, slice);
                 _envCells.Render(WbRenderPass.Opaque, _oneCell);
@@ -417,6 +425,11 @@ public sealed class RetailPViewRenderer
             _oneCell.Clear();
             _oneCell.Add(cellId);
 
+            // BR-2 phantom-site probe: entity buckets draw unclipped +
+            // un-viewcone'd by design — log the per-cell exposure.
+            if (AcDream.Core.Rendering.RenderingDiagnostics.ProbePhantomEnabled)
+                EmitPhantomObjsProbe(cellId, bucket.Count);
+
             UseIndoorMembershipOnlyRouting();
             DrawEntityBucket(ctx, bucket, _oneCell);
 
@@ -425,6 +438,38 @@ public sealed class RetailPViewRenderer
         }
     }
 
+    // BR-2 phantom-site probe state: print-on-change per cell so the log stays
+    // diffable while the condition persists. Throwaway apparatus — strip when
+    // the #113 phantom residual closes (plan §BR-2).
+    private readonly Dictionary<uint, string> _phantomShellSig = new();
+    private readonly Dictionary<uint, int> _phantomObjsSig = new();
+
+    private void EmitPhantomShellProbe(uint cellId, ClipViewSlice[] slices, bool clipShells, bool hadSlot)
+    {
+        var sb = new System.Text.StringBuilder(96);
+        sb.Append(clipShells ? "clip=on" : "clip=OFF");
+        sb.Append(hadSlot ? " slot=yes" : " slot=NONE(pass-all)");
+        sb.Append(" slices=[");
+        for (int i = 0; i < slices.Length; i++)
+        {
+            if (i > 0) sb.Append(',');
+            sb.Append(slices[i].Slot).Append(':').Append(slices[i].Planes.Length).Append("pl");
+            if (slices[i].Slot == 0) sb.Append("(PASS-ALL)");
+        }
+        sb.Append(']');
+        var sig = sb.ToString();
+        if (_phantomShellSig.TryGetValue(cellId, out var prev) && prev == sig) return;
+        _phantomShellSig[cellId] = sig;
+        Console.WriteLine($"[phantom-shell] cell=0x{cellId:X8} {sig}");
+    }
+
+    private void EmitPhantomObjsProbe(uint cellId, int bucketCount)
+    {
+        if (_phantomObjsSig.TryGetValue(cellId, out var prev) && prev == bucketCount) return;
+        _phantomObjsSig[cellId] = bucketCount;
+        Console.WriteLine($"[phantom-objs] cell=0x{cellId:X8} entities={bucketCount} (drawn unclipped, no viewcone)");
+    }
+
     private static ClipViewSlice[] GetCellSlicesOrNoClip(
         ClipFrameAssembly clipAssembly,
         uint cellId)

src/AcDream.Core/Rendering/RenderingDiagnostics.cs

@@ -198,6 +198,24 @@ public static class RenderingDiagnostics
     public static bool ProbePortalChurnEnabled { get; set; } =
         Environment.GetEnvironmentVariable("ACDREAM_PROBE_PORTAL_CHURN") == "1";
 
+    /// <summary>
+    /// BR-2 phantom-site probe (2026-06-11; plan
+    /// <c>docs/plans/2026-06-11-building-render-port-plan.md</c> §BR-2 first
+    /// task). The BR-1 pre-check proved the #113 phantom residual cannot be
+    /// GfxObj portal fills (never extracted); the surviving suspects are
+    /// cell-side. When true, <c>RetailPViewRenderer</c> emits, print-on-change
+    /// per cell: <c>[phantom-shell]</c> — per shell-pass cell, the clip-enable
+    /// state and each drawn slice's slot + plane count, flagging the pass-all
+    /// cases (NoClipSlice fallback for slot-less cells; assembler slot-0
+    /// scissor fallback) — and <c>[phantom-objs]</c> — per object-list cell,
+    /// the entity-bucket size drawn unclipped/un-viewcone'd. Reproducing the
+    /// phantom with this on pins which mechanism draws it (shells → BR-2/BR-3;
+    /// statics → BR-5). Throwaway apparatus — strip when the phantom closes.
+    /// Initial state from <c>ACDREAM_PROBE_PHANTOM=1</c>.
+    /// </summary>
+    public static bool ProbePhantomEnabled { get; set; } =
+        Environment.GetEnvironmentVariable("ACDREAM_PROBE_PHANTOM") == "1";
+
     // Cell-change gate for EmitVis. The probe fires once per distinct root cell
     // so launch.log stays readable under motion (the per-frame call is a no-op
     // when the root is unchanged). Sentinel 0 = "no root yet" — the first real