islaApocalypse-v2/Tools/Scripts/ShapingOracle.cs

using System;
using System.Collections.Generic;
using IslaApocalypse.Core;

namespace IslaApocalypse.Tools
{
	/// <summary>
	/// ⭐⭐ THE ORACLE — the automatic correctness checks that let the developer's eye judge ONLY
	/// relief.
	///
	/// ═══ WHY THIS EXISTS AT ALL ═══
	///
	/// The prototype's single most valuable terrain lesson was not about terrain:
	///
	/// > *"Five rounds of taste-iteration were safe BECAUSE correctness was not being judged by eye.
	/// > Where a future phase has a subjective gate, ask first what the automatic invariant is."*
	/// > — `Design - Tooling - Iteration and Batching.md`, "build the oracle before the
	/// >   taste-iteration, not after".
	///
	/// The curve is a subjective gate. So before a single render is looked at, four things are
	/// proven mechanically:
	///
	///   (a) REGRESSION       curve OFF is bit-identical to Phase 1's pass-1 output.
	///                        ⇒ the port disturbed nothing upstream.
	///   (b) CLASSIFY FIDELITY the classify field is bit-identical to the raw pre-curve field,
	///                        curve on or off. ⇒ the oracle field is actually an oracle.
	///   (c) MONOTONICITY     the effective per-seed curve is strictly increasing everywhere.
	///                        ⇒ no peak has become a pit.
	///   (d) BAND SHARES      realized land shares match the 60/13/10/5/8/3/1 targets.
	///                        ⇒ the calibration did what it claimed.
	///
	/// ⚠ BIT-IDENTICAL MEANS BIT-IDENTICAL. These compare IEEE-754 bit patterns, not values within
	/// an epsilon. "Close enough" is how a drift becomes a fact — and the whole point of the `.f32`
	/// dump is that two generators agree or their dumps differ.
	///
	/// ⚠ Any failure fails the TASK, loudly. Nothing here papers over a mismatch: a check that
	/// reports "mostly passed" is a check that has stopped working.
	/// </summary>
	public static class ShapingOracle
	{
		/// <summary>One check's verdict. <see cref="Detail"/> carries the evidence either way.</summary>
		public sealed class Check
		{
			public string Id;          // "a", "b", "c", "d"
			public string Name;
			public bool Passed;
			public string Detail;

			public override string ToString() => $"[{(Passed ? "PASS" : "FAIL")}] ({Id}) {Name} — {Detail}";
		}

		/// <summary>
		/// Compare two float fields for BIT equality. Returns the number of differing cells and the
		/// first difference found, so a failure is actionable rather than just red.
		/// </summary>
		public static (long differing, string firstDiff) CompareBitwise(float[,] a, float[,] b, int mapSize)
		{
			long differing = 0;
			string first = null;

			for (int x = 0; x < mapSize; x++)
			{
				for (int y = 0; y < mapSize; y++)
				{
					int ba = BitConverter.SingleToInt32Bits(a[x, y]);
					int bb = BitConverter.SingleToInt32Bits(b[x, y]);
					if (ba == bb) continue;

					differing++;
					first ??= $"first at [{x},{y}]: {a[x, y]:G9} (0x{ba:X8}) vs {b[x, y]:G9} (0x{bb:X8})";
				}
			}
			return (differing, first);
		}

		/// <summary>
		/// (a) REGRESSION — with the curve off, shaping must return the pass-1 field untouched.
		///
		/// ⚠ This is the WEAKER, always-available half of check (a): it proves pass 2 is a no-op when
		/// gated off. The stronger half — that pass 1 ITSELF still matches Phase 1 byte-for-byte — is
		/// <see cref="RegressionAgainstDump"/>, which needs a Phase-1 `.f32` on disk.
		/// </summary>
		public static Check RegressionCurveOff(Pass1Result p1, Pass2Result offResult)
		{
			var c = new Check { Id = "a", Name = "regression: curve OFF == pass-1 output" };

			if (offResult.CurveOn)
			{
				c.Passed = false;
				c.Detail = "the result handed in was generated with the curve ON — wrong variant.";
				return c;
			}

			var (differing, firstDiff) = CompareBitwise(p1.Height, offResult.Height, p1.MapSize);
			bool aliased = offResult.FieldsAreAliased;

			c.Passed = differing == 0;
			c.Detail = c.Passed
				? $"bit-identical over {(long)p1.MapSize * p1.MapSize:N0} cells" +
				  (aliased ? " (and the fields alias one array, as the reference did)" : "")
				: $"{differing:N0} cells differ — {firstDiff}";
			return c;
		}

		/// <summary>
		/// (a′) REGRESSION against a Phase-1 `.f32` dump — the cross-run half.
		///
		/// ⚠ A MISSING DUMP IS NOT A PASS. It is reported as INCONCLUSIVE and the caller says so; a
		/// check that silently succeeds when its input is absent is worse than no check, because it
		/// buys confidence that was never earned.
		/// </summary>
		public static Check RegressionAgainstDump(float[,] current, float[,] phase1Dump, int mapSize, string dumpPath)
		{
			var c = new Check { Id = "a′", Name = "regression: pass-1 == Phase-1 .f32 dump" };

			if (phase1Dump == null)
			{
				c.Passed = false;
				c.Detail = $"INCONCLUSIVE — no readable Phase-1 dump at {dumpPath} for this seed/size. " +
						   "Not counted as a pass; set ISLA_PHASE1_SOURCE to a batch that has one.";
				return c;
			}

			var (differing, firstDiff) = CompareBitwise(phase1Dump, current, mapSize);
			c.Passed = differing == 0;
			c.Detail = c.Passed
				? $"bit-identical to {dumpPath} over {(long)mapSize * mapSize:N0} cells"
				: $"{differing:N0} cells differ from {dumpPath} — {firstDiff}";
			return c;
		}

		/// <summary>
		/// (b) CLASSIFY FIDELITY — the classify field is the raw pre-curve field, bit-for-bit, with
		/// the curve on or off.
		///
		/// This is the invariant every later phase's oracle rests on: biomes and water will classify
		/// from this field, so if it has drifted by even one ulp the "md5-identical across shaping
		/// changes" guarantee is gone before it is ever used.
		/// </summary>
		public static Check ClassifyFidelity(Pass1Result p1, Pass2Result p2)
		{
			var c = new Check { Id = "b", Name = "classify field == raw pass-1 field" };

			var (differing, firstDiff) = CompareBitwise(p1.Height, p2.HeightClassify, p1.MapSize);
			c.Passed = differing == 0;
			c.Detail = c.Passed
				? $"bit-identical over {(long)p1.MapSize * p1.MapSize:N0} cells (curve {(p2.CurveOn ? "ON" : "OFF")})"
				: $"{differing:N0} cells differ — {firstDiff}";
			return c;
		}

		/// <summary>
		/// (c) MONOTONICITY — recorded rather than re-run.
		///
		/// <c>HeightCurve.AssertMonotonic</c> THROWS on violation and is called inside
		/// <see cref="Shaping.Shape"/>, so reaching this code at all means the sweep passed. The
		/// check exists so the oracle table states it explicitly instead of leaving the strongest
		/// guarantee implicit in the absence of a crash.
		/// </summary>
		public static Check Monotonicity(Pass2Result p2)
		{
			var c = new Check { Id = "c", Name = "curve strictly monotonic (24-corner sweep)" };

			if (!p2.CurveOn)
			{
				c.Passed = true;
				c.Detail = "curve off — nothing to prove (identity is trivially monotonic).";
				return c;
			}

			string note = p2.Notes.Find(n => n.Contains("Monotonicity assertion passed"));
			c.Passed = note != null;
			c.Detail = note ?? "no monotonicity confirmation recorded — AssertMonotonic did not run.";
			return c;
		}

		/// <summary>
		/// (d) BAND SHARES — the realized land shares against the M3 targets.
		///
		/// ⚠ MEASURED ON THE RAW (INPUT) DISTRIBUTION, because that is where the knots cut. The
		/// shares are exact by construction IF the quantile machinery is right — so this check is
		/// really a proof that <see cref="LandHistogram"/> measured what it claimed, which is the one
		/// thing the reference could never verify about its own knots.
		/// </summary>
		/// <param name="tolerancePercentagePoints">
		/// Allowed absolute deviation per band, in percentage points. The knots come from the SAME
		/// histogram, so agreement is limited only by in-bin interpolation — tenths of a point, not
		/// whole ones.
		/// </param>
		public static Check BandShares(LandHistogram raw, CurveKnots k, double tolerancePercentagePoints)
		{
			var c = new Check { Id = "d", Name = "realized land band shares == 60/13/10/5/8/3/1 targets" };

			double[] realized = RealizedShares(raw, k);
			double worst = 0.0;
			int worstBand = -1;

			for (int i = 0; i < realized.Length; i++)
			{
				double d = Math.Abs(realized[i] - CurveKnots.BandShareTargets[i]);
				if (d > worst) { worst = d; worstBand = i; }
			}

			c.Passed = worst <= tolerancePercentagePoints;
			c.Detail = $"worst band '{CurveKnots.BandNames[worstBand]}' off by {worst:F3} pp " +
					   $"(tolerance {tolerancePercentagePoints:F2} pp); realized " +
					   string.Join("/", Array.ConvertAll(realized, v => v.ToString("F2")));
			return c;
		}

		/// <summary>
		/// The fraction of land, in percent, falling in each of the curve's seven INPUT bands.
		/// Band edges are sea, K1..K6, +∞.
		/// </summary>
		public static double[] RealizedShares(LandHistogram raw, CurveKnots k)
		{
			float[] edges = { raw.SeaLevel, k.K1, k.K2, k.K3, k.K4, k.K5, k.K6 };
			var shares = new double[7];

			for (int i = 0; i < 6; i++)
				shares[i] = raw.FractionBetween(edges[i], edges[i + 1]) * 100.0;

			shares[6] = Math.Max(0.0, (1.0 - raw.FractionBelow(k.K6)) * 100.0);
			return shares;
		}

		/// <summary>
		/// A bit-regression against any `.f32` dump, with the caller naming the check — the
		/// chat2/02 generalization of <see cref="RegressionAgainstDump"/>, used to hold the
		/// staircase mode against task 01's own batch output. The same rule applies: a missing dump
		/// is INCONCLUSIVE and counted as a failure, never as a pass.
		/// </summary>
		public static Check DumpRegression(string id, string name, float[,] current, float[,] dump,
			int mapSize, string dumpPath)
		{
			var c = new Check { Id = id, Name = name };

			if (dump == null)
			{
				c.Passed = false;
				c.Detail = $"INCONCLUSIVE — no readable dump at {dumpPath} for this seed/size. Not counted as a pass.";
				return c;
			}

			var (differing, firstDiff) = CompareBitwise(dump, current, mapSize);
			c.Passed = differing == 0;
			c.Detail = c.Passed
				? $"bit-identical to {dumpPath} over {(long)mapSize * mapSize:N0} cells"
				: $"{differing:N0} cells differ from {dumpPath} — {firstDiff}";
			return c;
		}

		/// <summary>
		/// (d) ⭐ LOWLANDS PRESERVED — the rev-3 task's load-bearing check. For every cell whose RAW
		/// height is at or below K2 (the toe+red band the developer likes), the continuous mode's
		/// output must be BIT-IDENTICAL to the staircase's. This mechanically enforces "do not lift
		/// the lowlands": the low pile cannot move if its every column is the same float.
		///
		/// The identity is by construction — the continuous curve DELEGATES to the staircase's own
		/// toe+red code path below K2 — and this check is what keeps that construction honest
		/// against refactoring, float re-association, or a ceiling knob bug.
		///
		/// ⚠ Run against the LIFTED_WRONG bookend this check is EXPECTED to fail — the caller
		/// reports that failure as confirmation of the wrong direction, not as a defect.
		/// </summary>
		public static Check LowlandsPreserved(Pass1Result p1, Pass2Result staircase, Pass2Result variant)
		{
			var c = new Check { Id = "d", Name = $"lowlands (raw ≤ K2) bit-identical to staircase [{variant.VariantLabel}]" };

			float k2 = staircase.Knots.K2;
			long compared = 0, differing = 0;
			string first = null;

			for (int x = 0; x < p1.MapSize; x++)
			{
				for (int y = 0; y < p1.MapSize; y++)
				{
					if (p1.Height[x, y] > k2) continue;
					compared++;
					int ba = BitConverter.SingleToInt32Bits(staircase.Height[x, y]);
					int bb = BitConverter.SingleToInt32Bits(variant.Height[x, y]);
					if (ba == bb) continue;
					differing++;
					first ??= $"first at [{x},{y}] raw {p1.Height[x, y]:G9}: " +
							  $"staircase {staircase.Height[x, y]:G9} vs {variant.Height[x, y]:G9}";
				}
			}

			c.Passed = differing == 0;
			c.Detail = c.Passed
				? $"bit-identical over all {compared:N0} lowland cells (raw ≤ K2 = {k2:F6})"
				: $"{differing:N0} of {compared:N0} lowland cells differ — {first}";
			return c;
		}

		/// <summary>
		/// (e) UPPER CONTINUOUS — sample the climb's slope densely; no near-flat anywhere (a bench
		/// reborn), no cliff below the summit onset (the summit itself may steepen — that is the
		/// dramatic peak). ⚠ SOFT: this is an exploration batch, so a violation warns loudly and
		/// lands in the report rather than failing the run — the tool decides the exit code.
		/// </summary>
		public static Check UpperClimbProfile(Pass2Result p2)
		{
			var c = new Check { Id = "e", Name = $"upper climb continuous — no flats, no low-mid cliffs [{p2.VariantLabel}]" };

			if (p2.Continuous == null)
			{
				c.Passed = false;
				c.Detail = "no continuous spline on this result — wrong mode handed in.";
				return c;
			}

			var (minN, minAt, maxN, maxAt, nearFlat, cliff) = p2.Continuous.SampleClimbSlopes();
			c.Passed = !nearFlat && !cliff;
			c.Detail = $"slope (normalized, 1 = climb average): min {minN:F3} at raw {minAt:F4}" +
					   $"{(nearFlat ? " ⚠ NEAR-FLAT (a bench reborn)" : "")}, " +
					   $"max below onset {maxN:F3} at raw {maxAt:F4}" +
					   $"{(cliff ? " ⚠ CLIFF below the summit onset" : "")}";
			return c;
		}

		/// <summary>
		/// (f) SEA IDENTITY — per cell, not per count: a column is land in the variant exactly when
		/// it is land with the curve off. Counting alone could hide two errors that cancel; this
		/// cannot. The coastline is the one thing every mode, including the wrong one, must keep.
		/// </summary>
		public static Check SeaIdentity(Pass2Result off, Pass2Result variant, float seaLevel)
		{
			var c = new Check { Id = "f", Name = $"sea identity — per-cell landness unchanged [{variant.VariantLabel}]" };

			long mismatches = 0;
			string first = null;
			for (int x = 0; x < off.MapSize; x++)
			{
				for (int y = 0; y < off.MapSize; y++)
				{
					bool a = off.Height[x, y] >= seaLevel;
					bool b = variant.Height[x, y] >= seaLevel;
					if (a == b) continue;
					mismatches++;
					first ??= $"first at [{x},{y}]: off {off.Height[x, y]:G9} vs {variant.Height[x, y]:G9}";
				}
			}

			c.Passed = mismatches == 0;
			c.Detail = c.Passed
				? $"per-cell landness identical over {(long)off.MapSize * off.MapSize:N0} cells"
				: $"{mismatches:N0} cells changed sides of the waterline — {first}";
			return c;
		}

		/// <summary>
		/// (g) ⭐ MOUNTAIN RESTORED (chat2/03) — how much land ends up above 100 m and 220 m,
		/// against the staircase's own figures.
		///
		/// ═══ ⚠ REPORTED, NOT GATED ═══
		///
		/// This is a taste target the developer tunes, so a miss is a FINDING, not a build failure —
		/// gating it would make `mountainLift` unusable as a knob, since every value but one would
		/// fail the run. What it must never do is stay silent: chat2/02 lost two thirds of the
		/// mountain and only found out because someone went looking at the dumps afterwards. This
		/// check is that look, made automatic.
		///
		/// <paramref name="tolerancePp"/> only decides whether the row reads PASS or NOTE; the
		/// numbers are always printed.
		/// </summary>
		public static Check MountainRestored(Pass2Result variant, Pass2Result staircase,
			float seaLevel, double tolerancePp)
		{
			var c = new Check { Id = "g", Name = $"mountain restored vs staircase [{variant.VariantLabel}]" };

			var (v100, v220) = LandAbove(variant, seaLevel);
			var (s100, s220) = LandAbove(staircase, seaLevel);

			double d100 = v100 - s100;
			c.Passed = Math.Abs(d100) <= tolerancePp;
			c.Detail = $">100 m: {v100:F2} % vs staircase {s100:F2} % ({d100:+0.00;-0.00} pp) · " +
					   $">220 m: {v220:F2} % vs {s220:F2} % ({v220 - s220:+0.00;-0.00} pp)";
			return c;
		}

		/// <summary>Percentage of LAND above 100 m and 220 m of world height. Land = at/above sea.</summary>
		public static (double above100, double above220) LandAbove(Pass2Result p2, float seaLevel)
		{
			float t100 = seaLevel + WorldScale.RawFromMetres(100f);
			float t220 = seaLevel + WorldScale.RawFromMetres(220f);

			long land = 0, a100 = 0, a220 = 0;
			for (int x = 0; x < p2.MapSize; x++)
			{
				for (int y = 0; y < p2.MapSize; y++)
				{
					float h = p2.Height[x, y];
					if (h < seaLevel) continue;
					land++;
					if (h > t100) a100++;
					if (h > t220) a220++;
				}
			}
			return land == 0 ? (0.0, 0.0) : (100.0 * a100 / land, 100.0 * a220 / land);
		}

		// ═══ chat2/05 — the offshore checks ═══

		// (h) was the chat2/05 seeded-floor check — reverted out with the floor in chat2/06. No
		// count is guaranteed any more, so there is nothing for an oracle to assert; the count
		// table is the evidence, and it is statistics, not a check.

		/// <summary>
		/// (i) ⭐ MOAT INTACT — no offshore island is 8-connected to mainland land. The moat exists
		/// to make a land bridge impossible; this is the proof that it did.
		/// </summary>
		public static Check MoatIntact(Pass1Result p1, List<IslandComponent> comps)
		{
			var c = new Check { Id = "i", Name = "moat intact — no island touches the mainland" };
			int bridged = OffshoreAnalysis.BridgedCount(comps);
			c.Passed = p1.HasIslandTag && bridged == 0;
			c.Detail = !p1.HasIslandTag ? "no island tag — nothing to check"
					 : bridged == 0 ? $"all {comps.Count} islands are separated from mainland by water"
					 : $"{bridged} island(s) BRIDGE to mainland land";
			return c;
		}

		/// <summary>
		/// (j) ⭐ MAINLAND UNMOVED — with offshore on vs off, every cell that was LAND with it off is
		/// BIT-IDENTICAL with it on. The shelf touches only below-sea cells, the islets only lift
		/// below-sea cells; neither may touch existing land. (The falloff test and the moat did their
		/// job if this holds.) Reports how many sea cells the shelf moved and how many were lifted.
		/// </summary>
		public static Check MainlandUnmoved(Pass1Result off, Pass1Result on, float sea)
		{
			var c = new Check { Id = "j", Name = "mainland unmoved — every offshore-OFF land cell bit-identical with offshore ON" };
			long land = 0, landDiff = 0, seaChanged = 0, lifted = 0;
			string first = null;
			for (int x = 0; x < off.MapSize; x++)
			{
				for (int y = 0; y < off.MapSize; y++)
				{
					float a = off.Height[x, y], b = on.Height[x, y];
					if (a >= sea)
					{
						land++;
						if (BitConverter.SingleToInt32Bits(a) != BitConverter.SingleToInt32Bits(b))
						{
							landDiff++;
							first ??= $"first at [{x},{y}]: {a:G9} → {b:G9}";
						}
					}
					else
					{
						if (a != b) seaChanged++;
						if (b >= sea) lifted++;
					}
				}
			}
			c.Passed = landDiff == 0;
			c.Detail = landDiff == 0
				? $"all {land:N0} land cells bit-identical; {seaChanged:N0} sea cells remapped by the shelf, {lifted:N0} lifted to land"
				: $"{landDiff:N0} of {land:N0} land cells CHANGED — {first}";
			return c;
		}

		/// <summary>
		/// (k) TAG ↔ COASTLINE CONSISTENT — per cell, classify-land ⇔ render-land (the curve is
		/// identity at sea and monotone above, so it must be — D-046), and every TAGGED cell is land
		/// in both fields. This is what lets the tag be carried through pass 2 without recomputation.
		/// </summary>
		public static Check TagCoastlineConsistent(Pass2Result p2, float sea)
		{
			var c = new Check { Id = "k", Name = "offshore tag: classify/render coastline consistent, every tagged cell is land" };
			long mismatch = 0, tagNotLand = 0, tagged = 0;
			for (int x = 0; x < p2.MapSize; x++)
			{
				for (int y = 0; y < p2.MapSize; y++)
				{
					bool cl = p2.HeightClassify[x, y] >= sea;
					bool rl = p2.Height[x, y] >= sea;
					if (cl != rl) mismatch++;
					if (p2.IsIsland != null && p2.IsIsland[x, y])
					{
						tagged++;
						if (!cl || !rl) tagNotLand++;
					}
				}
			}
			c.Passed = mismatch == 0 && tagNotLand == 0;
			c.Detail = $"{mismatch:N0} classify/render landness mismatches; {tagNotLand:N0} of {tagged:N0} tagged cells not land";
			return c;
		}

		/// <summary>
		/// (l) HMaxSeed RECOMPUTED AFTER SHELF + OFFSHORE — reported. Expected unchanged (a ~34 m
		/// crest vs a ~290 m peak), but the ORDER is the fix (chat2/00 Drift §2), and the value is
		/// measured rather than assumed. Always passes; the detail is the point.
		/// </summary>
		public static Check HMaxAfterOffshore(Pass1Result p1)
		{
			bool moved = p1.HMaxSeed != p1.HMaxSeedBeforeOffshore;
			return new Check
			{
				Id = "l", Name = "HMaxSeed recomputed after shelf + offshore",
				Passed = true,
				Detail = $"before {p1.HMaxSeedBeforeOffshore:F6} → after {p1.HMaxSeed:F6} " +
						 (moved ? "— ⚠ MOVED (an islet outran the peak?)" : "— unchanged, as expected; the ORDER is now right by construction"),
			};
		}

		// ═══ chat2/07 — the region checks ═══

		/// <summary>(m) CENTRE IS LAND — the mainland definition held (the massif is centred); the fallback was not needed.</summary>
		public static Check CentreIsLand(Pass1Result p1)
		{
			var c = new Check { Id = "m", Name = "mainland = centre component (centre cell is land, no fallback)" };
			if (p1.Regions == null) { c.Passed = false; c.Detail = "no region labeling on this field"; return c; }
			var m = p1.Regions.Mainland;
			c.Passed = p1.Regions.CentreWasLand && m != null && (p1.RegionLedger == null || p1.RegionLedger.CentreWasLandPre);
			c.Detail = c.Passed
				? $"centre is land; mainland id {p1.Regions.MainlandId}, {m.SizeCells:N0} cells, centroid ({m.CentroidX:F0},{m.CentroidY:F0}); {p1.Regions.IslandCount} islands"
				: "⚠ CENTRE CELL IS NOT LAND — fell back to the largest component";
			return c;
		}

		/// <summary>
		/// (n) ⭐ THE REVERT GUARDS, RE-PROVEN ON THE FIELDS — filter OFF vs ON: every cell of the OFF
		/// field's MAINLAND component is bit-identical; every cell that changed was land in a
		/// sub-threshold NON-MAINLAND component of the OFF labeling (component-only) and went DOWN, to
		/// below sea (lower-only); nothing else moved. The pass asserted this as it ran; this is the
		/// independent proof on the finished fields.
		/// </summary>
		public static Check RevertGuards(Pass1Result off, Pass1Result on, float sea, long thresholdCells)
		{
			var c = new Check { Id = "n", Name = "speck revert: mainland bit-identical, every change is in a sub-threshold island and lower-only" };
			if (off.Regions == null) { c.Passed = false; c.Detail = "the OFF field has no region labeling"; return c; }
			int n = off.MapSize;
			var lab = off.Regions;
			long mainland = 0, mainlandDiff = 0, changed = 0, notIsland = 0, notSmall = 0, raised = 0, notSea = 0;
			string first = null;
			for (int x = 0; x < n; x++)
			{
				for (int y = 0; y < n; y++)
				{
					float a = off.Height[x, y], b = on.Height[x, y];
					int id = lab.Id[x * n + y];
					bool isMain = id != 0 && id == lab.MainlandId;
					if (isMain) mainland++;
					if (BitConverter.SingleToInt32Bits(a) == BitConverter.SingleToInt32Bits(b)) continue;
					changed++;
					if (isMain) { mainlandDiff++; first ??= $"mainland cell [{x},{y}] {a:G9} → {b:G9}"; continue; }
					if (id == 0) { notIsland++; first ??= $"sea cell [{x},{y}] changed {a:G9} → {b:G9}"; continue; }
					if (lab.Regions[id - 1].SizeCells >= thresholdCells) { notSmall++; first ??= $"cell [{x},{y}] of component {id} ({lab.Regions[id - 1].SizeCells} cells ≥ {thresholdCells}) changed"; }
					if (b >= a) { raised++; first ??= $"cell [{x},{y}] RAISED {a:G9} → {b:G9}"; }
					if (b >= sea) { notSea++; first ??= $"cell [{x},{y}] still land after revert ({b:G9})"; }
				}
			}
			c.Passed = mainlandDiff == 0 && notIsland == 0 && notSmall == 0 && raised == 0 && notSea == 0;
			c.Detail = c.Passed
				? $"all {mainland:N0} mainland cells bit-identical; {changed:N0} cells changed, every one in a sub-threshold island, lowered below sea"
				: $"VIOLATION — mainland {mainlandDiff:N0} / non-island {notIsland:N0} / over-threshold {notSmall:N0} / raised {raised:N0} / still land {notSea:N0} — {first}";
			return c;
		}

		/// <summary>(o) LABELS DETERMINISTIC — two generations of the same seed: id maps and component tables identical.</summary>
		public static Check LabelsDeterministic(Pass1Result a, Pass1Result b)
		{
			var c = new Check { Id = "o", Name = "region ids deterministic per seed (two runs, id map + table identical)" };
			if (a.Regions == null || b.Regions == null) { c.Passed = false; c.Detail = "no region labeling"; return c; }
			long diff = 0; int n = a.MapSize;
			for (int i = 0; i < n * n; i++) if (a.Regions.Id[i] != b.Regions.Id[i]) diff++;
			bool table = a.Regions.Regions.Count == b.Regions.Regions.Count && a.Regions.MainlandId == b.Regions.MainlandId;
			if (table)
				for (int i = 0; i < a.Regions.Regions.Count; i++)
				{
					var ra = a.Regions.Regions[i]; var rb = b.Regions.Regions[i];
					if (ra.SizeCells != rb.SizeCells || ra.CentroidX != rb.CentroidX || ra.CentroidY != rb.CentroidY || ra.Hemisphere != rb.Hemisphere || ra.IsMainland != rb.IsMainland) { table = false; break; }
				}
			c.Passed = diff == 0 && table;
			c.Detail = c.Passed ? $"{a.Regions.Regions.Count} components, id map identical over {(long)n * n:N0} cells, tables identical"
								: $"{diff:N0} id cells differ; tables {(table ? "identical" : "DIFFER")}";
			return c;
		}

		// ═══ chat2/08 — the southern-stretch band checks ═══

		/// <summary>
		/// (p) ⭐ NORTH BIT-LOCKED, BOTH DIRECTIONS — every cell with y &lt; <paramref name="bandRow"/> is
		/// bit-identical between the two fields (no land lowered, no sea raised); reports how many cells
		/// differ at/below the band (allowed — that is the relaxation). The surgical guarantee, per cell.
		/// </summary>
		public static Check NorthLocked(string id, string name, float[,] a, float[,] b, int mapSize, int bandRow)
		{
			var c = new Check { Id = id, Name = name };
			long northDiff = 0, southDiff = 0, north = 0; string first = null;
			for (int x = 0; x < mapSize; x++)
				for (int y = 0; y < mapSize; y++)
				{
					bool same = BitConverter.SingleToInt32Bits(a[x, y]) == BitConverter.SingleToInt32Bits(b[x, y]);
					if (y < bandRow) { north++; if (!same) { northDiff++; first ??= $"[{x},{y}] {a[x, y]:G9} vs {b[x, y]:G9}"; } }
					else if (!same) southDiff++;
				}
			c.Passed = northDiff == 0;
			c.Detail = c.Passed
				? $"all {north:N0} cells north of row {bandRow} bit-identical; {southDiff:N0} cells differ in the band or below (the relaxation)"
				: $"{northDiff:N0} cells north of row {bandRow} DIFFER — {first}";
			return c;
		}

		/// <summary>(q) ⭐ NORTHERN ISLANDS INVARIANT — the multiset of north-hemisphere island components (size, centroid) is identical between two labelings.</summary>
		public static Check NorthIslandsInvariant(string name, RegionLabels a, RegionLabels b)
		{
			var c = new Check { Id = "q", Name = name };
			if (a == null || b == null) { c.Passed = false; c.Detail = "no region labeling"; return c; }
			var sa = NorthSet(a); var sb = NorthSet(b);
			bool same = sa.Count == sb.Count;
			if (same) for (int i = 0; i < sa.Count; i++) if (sa[i] != sb[i]) { same = false; break; }
			c.Passed = same;
			c.Detail = same ? $"{sa.Count} northern islands, identical (size + centroid)" : $"DIFFER — {sa.Count} vs {sb.Count} northern islands, or a size/centroid moved";
			return c;
		}

		private static List<string> NorthSet(RegionLabels l)
		{
			var list = new List<string>();
			foreach (var r in l.Regions)
				if (!r.IsMainland && r.Hemisphere == RegionLabeling.HemiNorth)
					list.Add($"{r.SizeCells}:{r.CentroidX:F3}:{r.CentroidY:F3}");
			list.Sort(StringComparer.Ordinal);
			return list;
		}

		/// <summary>Render the whole oracle as a markdown table for the INDEX and the report.</summary>
		public static string ToMarkdownTable(IEnumerable<Check> checks)
		{
			var sb = new System.Text.StringBuilder();
			sb.AppendLine("| | Check | Result | Evidence |");
			sb.AppendLine("|---|---|---|---|");
			foreach (Check c in checks)
				sb.AppendLine($"| `{c.Id}` | {c.Name} | **{(c.Passed ? "PASS" : "FAIL")}** | {c.Detail} |");
			return sb.ToString();
		}
	}
}