diag #181: root-cause chain complete - flapping cell 0x0181, wall-press excitation, and the REAL defect: camera-flood-scoped light application

Issue181VisFlapReplayTests: headless flood replay at the live parked pose names cell 0x8A020181 - +-0.5mm eye perturbations flip its admission (at yaw15/pitch-20 for every direction). Issue181CameraParkStabilityTests: the camera loop parks BIT-EXACT with static inputs (0.00um over 2000 frames) - the live ~1mm/frame wander is the wall-press equilibrium (sought steps a*gap ~4mm into the wall per frame, the clip lands within adjust_to_plane's parametric 0.02 window; player physics bit-frozen per [resolve]). That wobble is retail-class. The defect is OURS: the A7 adaptation scopes light application to the camera flood's per-frame admission, so a sliver cell flapping flips whole lit regions; retail computes light reach once at registration (Render::add_static_light -> CObjCell::add_lights), camera-independent. Fix direction: registration-time per-light reach sets via the portal graph (pseudocode docs/research/2026-07-06-a7-per-cell-lighting-pseudocode.md). ISSUES #181 updated with the full chain.

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

tests/AcDream.App.Tests/Rendering/Issue181VisFlapReplayTests.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Numerics;
+using AcDream.App.Rendering;
+using DatReaderWriter;
+using DatReaderWriter.Options;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace AcDream.App.Tests.Rendering;
+
+/// <summary>
+/// #181 — the portal-flood admitted set flaps 31↔32 on MICRON eye noise at a
+/// parked camera (live: launch-176-leakfix.log, root 0x8A020142, vis flips
+/// every ~100–200 frames for 517k frames; the swept eye carries ~7 µm
+/// float-roundtrip noise). The flapping cell's visibility-scoped lights + the
+/// union-AABB scissor rect strobe = the #176 washed-region flicker.
+///
+/// This replay hunts the knife edge headlessly: at the live parked eye
+/// (49.15, −38.62, −3.98), sweep gazes and perturb the eye by ±0.5 mm per
+/// axis; ANY admitted-set difference at sub-mm perturbation is the #181
+/// instability, and the symmetric difference names the flapping cell.
+/// </summary>
+public class Issue181VisFlapReplayTests
+{
+    private const uint FacilityHub = 0x8A020000u;
+    private const uint LiveRoot    = FacilityHub | 0x0142u;
+
+    private static readonly Vector3 LiveEye = new(49.15f, -38.62f, -3.98f);
+
+    private readonly ITestOutputHelper _out;
+    public Issue181VisFlapReplayTests(ITestOutputHelper output) => _out = output;
+
+    private static Matrix4x4 ViewProjFor(Vector3 eye, Vector3 gazeDir)
+    {
+        var view = Matrix4x4.CreateLookAt(eye, eye + gazeDir, Vector3.UnitZ);
+        var proj = Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 3f, 16f / 9f, 0.1f, 5000f);
+        return view * proj;
+    }
+
+    private static List<uint> Flood(
+        Dictionary<uint, LoadedCell> cells, uint rootId, Vector3 eye, Vector3 gazeDir)
+    {
+        Func<uint, LoadedCell?> lookup = id => cells.TryGetValue(id, out var c) ? c : null;
+        var frame = PortalVisibilityBuilder.Build(
+            cells[rootId], eye, lookup, ViewProjFor(eye, gazeDir),
+            buildingMembership: null,
+            drawLiftZ: PortalVisibilityBuilder.ShellDrawLiftZ);
+        var result = new List<uint>(frame.OrderedVisibleCells);
+        result.Sort();
+        return result;
+    }
+
+    private static string CellSetString(IEnumerable<uint> ids)
+        => string.Join(" ", ids.Select(id => $"{id & 0xFFFFu:X4}"));
+
+    [Fact]
+    public void Diagnostic_SubMillimeterEyePerturbation_MustNotChangeAdmission()
+    {
+        var datDir = CornerFloodReplayTests.ResolveDatDir();
+        if (datDir is null) { _out.WriteLine("SKIP: no dat dir"); return; }
+        using var dats = new DatCollection(datDir, DatAccessType.Read);
+        var cells = Issue120ReciprocalPingPongTests.LoadAllInteriorCells(dats, FacilityHub);
+        Assert.True(cells.ContainsKey(LiveRoot), "live root 0x0142 not loaded");
+
+        // ±0.5 mm per axis — an order of magnitude above the live µm noise, well
+        // below anything visually meaningful.
+        var perturbations = new[]
+        {
+            new Vector3( 0.0005f, 0, 0), new Vector3(-0.0005f, 0, 0),
+            new Vector3(0,  0.0005f, 0), new Vector3(0, -0.0005f, 0),
+            new Vector3(0, 0,  0.0005f), new Vector3(0, 0, -0.0005f),
+        };
+
+        int unstableGazes = 0;
+        for (int yawDeg = 0; yawDeg < 360; yawDeg += 15)
+        {
+            foreach (float pitchDeg in new[] { 0f, -20f, -35f })
+            {
+                float yaw = yawDeg * MathF.PI / 180f, pitch = pitchDeg * MathF.PI / 180f;
+                var gaze = new Vector3(
+                    MathF.Cos(pitch) * MathF.Cos(yaw),
+                    MathF.Cos(pitch) * MathF.Sin(yaw),
+                    MathF.Sin(pitch));
+
+                var baseline = Flood(cells, LiveRoot, LiveEye, gaze);
+                foreach (var d in perturbations)
+                {
+                    var perturbed = Flood(cells, LiveRoot, LiveEye + d, gaze);
+                    if (perturbed.SequenceEqual(baseline)) continue;
+
+                    unstableGazes++;
+                    var removed = baseline.Except(perturbed).ToList();
+                    var added   = perturbed.Except(baseline).ToList();
+                    _out.WriteLine(FormattableString.Invariant(
+                        $"UNSTABLE yaw={yawDeg} pitch={pitchDeg} d=({d.X * 1000:F1},{d.Y * 1000:F1},{d.Z * 1000:F1})mm base={baseline.Count} pert={perturbed.Count} removed=[{CellSetString(removed)}] added=[{CellSetString(added)}]"));
+                }
+            }
+        }
+
+        _out.WriteLine($"unstable (gaze, perturbation) pairs: {unstableGazes}");
+        // Diagnostic first: report, don't assert — the fix turns this into a hard pin.
+    }
+}