test(physics): P4 review - RestrictionObj prevalence inspection over the installed cell DAT

103,766 of 729,888 EnvCells (14%, 1,293 landblocks - the entire housing
estate, 0x70xxxxxx GUIDs) carry a baked RestrictionObj. The AP-71 gate
as wired (CanMoveInto unmodeled, fail-closed) would therefore lock every
housing interior for everyone; retail's CanMoveInto (0x0058da40) is
fail-OPEN for unowned houses and for a null RestrictionDB. Fix directed
back to the P4 implementer.

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

tests/AcDream.Core.Tests/Physics/RestrictionObjPrevalenceInspectionTests.cs

@@ -0,0 +1,94 @@
+using System.Collections.Generic;
+using AcDream.Core.Tests.Conformance;
+using DatReaderWriter;
+using DatReaderWriter.Options;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace AcDream.Core.Tests.Physics;
+
+/// <summary>
+/// AP-129 inspection (Campaign P P4 Opus review, 2026-07-30): measures how
+/// many EnvCells in the INSTALLED cell DAT actually carry a baked
+/// <c>RestrictionObj</c>. Decides the blast radius of the AP-71
+/// fail-closed gate: with <c>CanMoveInto</c> unmodeled (AP-129), every
+/// restricted cell refuses entry for every non-bypass player — harmless
+/// if the flag is rare/authored-for-housing-only, a live lockout if it is
+/// broadly baked into ordinary interiors. Inspection only; skips cleanly
+/// when the installed DATs are absent (CI), following the
+/// DoorSetupGfxObjInspectionTests pattern.
+/// </summary>
+public sealed class RestrictionObjPrevalenceInspectionTests
+{
+    private readonly ITestOutputHelper _output;
+
+    public RestrictionObjPrevalenceInspectionTests(ITestOutputHelper output)
+        => _output = output;
+
+    [Fact]
+    public void CountRestrictionObjCells_InstalledCellDat()
+    {
+        string? datDir = ConformanceDats.ResolveDatDir();
+        if (datDir is null)
+            return; // installed dats absent (CI) — skip cleanly
+
+        using var dats = new DatCollection(datDir, DatAccessType.Read);
+
+        // Bake-tool enumeration shape (BakeRunner.EnumerateEnvCellIds):
+        // LandBlockInfo (xxxxFFFE) NumCells ranges name every EnvCell id.
+        var landblockInfoIds = new List<uint>();
+        foreach (var file in dats.Cell.Tree)
+        {
+            if ((file.Id & 0xFFFFu) == 0xFFFEu)
+                landblockInfoIds.Add(file.Id);
+        }
+
+        int totalCells = 0;
+        int restricted = 0;
+        var restrictedLandblocks = new HashSet<uint>();
+        var samples = new List<string>();
+
+        foreach (uint infoId in landblockInfoIds)
+        {
+            if (!dats.Cell.TryGet<DatReaderWriter.DBObjs.LandBlockInfo>(
+                    infoId, out var info)
+                || info is null
+                || info.NumCells == 0)
+            {
+                continue;
+            }
+
+            uint firstCellId = (infoId & 0xFFFF_0000u) | 0x0100u;
+            for (uint offset = 0; offset < info.NumCells; offset++)
+            {
+                uint cellId = firstCellId + offset;
+                if (!dats.Cell.TryGet<DatReaderWriter.DBObjs.EnvCell>(
+                        cellId, out var cell)
+                    || cell is null)
+                {
+                    continue;
+                }
+
+                totalCells++;
+                if (cell.RestrictionObj != 0)
+                {
+                    restricted++;
+                    restrictedLandblocks.Add(cellId & 0xFFFF_0000u);
+                    if (samples.Count < 40)
+                    {
+                        samples.Add(
+                            $"cell 0x{cellId:X8} restrictionObj 0x{cell.RestrictionObj:X8}");
+                    }
+                }
+            }
+        }
+
+        _output.WriteLine(
+            $"EnvCells scanned: {totalCells}; with RestrictionObj != 0: "
+            + $"{restricted}; distinct landblocks: {restrictedLandblocks.Count}");
+        foreach (string s in samples)
+            _output.WriteLine(s);
+
+        Assert.True(totalCells > 0, "installed cell DAT enumerated no EnvCells");
+    }
+}