test(p0): threshold-trace golden wiring + PVS scaffold + P1-entry checklist

P0 Tasks 6 (autonomous half) + 7. FindCellList_DoorwayThreshold_MatchesRetailTrace
asserts acdream's pick == each captured retail pick; skips until the capture
fixture lands. PvsConformanceTests scaffolds the render visible-set golden
(skipped; filled in P4). ConformanceDats.FixturesDir resolves fixtures from the
source tree (issue98 pattern). Notes record: existing retail traces are
collision-only (no membership) so the strict P1 gate needs the one live capture;
plus the P1 re-scope finding (Stage-1 membership already on this branch).

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

tests/AcDream.Core.Tests/Conformance/ConformanceDats.cs

@@ -40,6 +40,27 @@ public static class ConformanceDats
         return Directory.Exists(def) ? def : null;
     }
 
+    /// <summary>
+    /// The conformance fixtures dir in the SOURCE tree (mirrors
+    /// CellarUpTrajectoryReplayTests.FixtureDir — fixtures are read from source,
+    /// not copied to the output dir).
+    /// </summary>
+    public static string FixturesDir =>
+        Path.Combine(SolutionRoot(), "tests", "AcDream.Core.Tests", "Conformance", "Fixtures");
+
+    private static string SolutionRoot()
+    {
+        var dir = AppContext.BaseDirectory;
+        while (!string.IsNullOrEmpty(dir))
+        {
+            if (File.Exists(Path.Combine(dir, "AcDream.slnx")))
+                return dir;
+            dir = Path.GetDirectoryName(dir);
+        }
+        throw new InvalidOperationException(
+            "Could not locate AcDream.slnx from " + AppContext.BaseDirectory);
+    }
+
     /// <summary>The physics-verbatim cell→world transform (no +2cm render lift).</summary>
     public static Matrix4x4 WorldTransform(DatEnvCell datCell) =>
         Matrix4x4.CreateFromQuaternion(datCell.Position.Orientation) *