fix: preserve orthogonal wall strips at multi-wall joins

Issue: #275
User-Visible: yes

scripts/mutation-gate.mjs

@@ -282,8 +282,12 @@ export const MUTANTS = [
       + 'offset origins recreates the measured white T-junction wedge from #261',
     patches: [{
       file: 'src/wall-thickness.ts',
-      find: '  const cuts = multiWallCutGeometry(multiWallBevelCutsAt(map, true, true));',
-      replace: '  const cuts = multiWallCutGeometry(multiWallBevelCutsAt(map, false, true));',
+      find: '      const cuts = multiWallEffectiveCutGeometry(\n'
+        + '        node, map, true, true, protectedStrips,\n'
+        + '      );',
+      replace: '      const cuts = multiWallEffectiveCutGeometry(\n'
+        + '        node, map, false, true, protectedStrips,\n'
+        + '      );',
     }, {
       file: 'src/wall-thickness.ts',
       find: '      if (envelope) localInside = intersection(localInside, envelope);\n'
@@ -292,6 +296,32 @@ export const MUTANTS = [
         + '      else if (envelope) localInside = intersection(localInside, envelope);',
     }],
   },
+  {
+    id: 'multi-wall-orthogonal-strip-protection-disabled',
+    guard: 'npx tsc -p tsconfig.test.json && node scripts/fix-test-build.mjs '
+      + '&& node --test --test-name-pattern="issue #275 preserves" '
+      + 'test/wall-thickness.test.mjs',
+    because: 'pairwise bevel cuts must exclude every finite strip with an orthogonal partner, '
+      + 'and the post-cut reconstruction is the independent fail-safe; disabling both recreates '
+      + 'the white notches and large missing wall areas from the exact #275 fixtures',
+    patches: [{
+      file: 'src/wall-thickness.ts',
+      find: '  return cuts && protectedStrips ? difference(cuts, protectedStrips) : cuts;',
+      replace: '  return cuts;',
+    }, {
+      file: 'src/wall-thickness.ts',
+      find: '      if (protectedStrips) local = union(local, protectedStrips);',
+      replace: '      // protected-strip fail-safe intentionally disabled by the mutant',
+    }, {
+      file: 'src/wall-thickness.ts',
+      find: '  if (protectedStrips) {\n'
+        + '    try {\n'
+        + '      let protectedInside = protectedStrips;',
+      replace: '  if (protectedStrips && false) {\n'
+        + '    try {\n'
+        + '      let protectedInside = protectedStrips;',
+    }],
+  },
   {
     id: 'multi-wall-finite-ray-disabled',
     guard: 'npx tsc -p tsconfig.test.json && node scripts/fix-test-build.mjs '
@@ -301,8 +331,8 @@ export const MUTANTS = [
       + 'node-wide 8H rectangle recreates the phantom wall and light barrier from #271',
     patches: [{
       file: 'src/wall-thickness.ts',
-      find: '          const supportExtent = Math.min(extent, support.length);',
-      replace: '          const supportExtent = extent;',
+      find: '      const supportExtent = Math.min(extent, support.length);',
+      replace: '      const supportExtent = extent;',
     }],
   },
   {
@@ -314,8 +344,8 @@ export const MUTANTS = [
       + 'white junction triangles from #272 while the old retained/discarded probes still pass',
     patches: [{
       file: 'src/wall-thickness.ts',
-      find: '        multiWallBevelCutsAt(nodeMap, true, true),',
-      replace: '        multiWallBevelCutsAt(nodeMap, true, false),',
+      find: '    multiWallBevelCutsAt(nodeMap, retainToLimit, connectToExterior),',
+      replace: '    multiWallBevelCutsAt(nodeMap, retainToLimit, false),',
     }],
   },
   {

scripts/smoke-links.mjs

@@ -46,12 +46,18 @@ export const SMOKE_LINKS = [
     symbols: [
       'multiWallBevelTriangles', 'multiWallBevelTrianglesAt',
       'buildMultiWallNodeMap', 'MultiWallNodeRay', 'MultiWallNodeRaySupport',
+      'multiWallProtectedRayIndexes', 'multiWallProtectedStripGeometry',
+      'multiWallProtectedMapGeometry', 'multiWallEffectiveCutGeometry',
+    ],
+    smokes: [
+      'smoke_junction_patch_resilience.mjs', 'smoke_multiwall_junction.mjs',
+      'smoke_multiwall_strip_containment.mjs',
     ],
-    smokes: ['smoke_junction_patch_resilience.mjs', 'smoke_multiwall_junction.mjs'],
     because: 'the #197 smoke probes the repaired exterior wedge across Plan, View, kiosk, '
       + 'Static, hidden Iso and light barriers, while the #249 smoke proves the old excessive '
-      + 'wedge stays empty, while #271 also proves finite ray endpoints across Plan, Static, '
-      + 'hidden Iso and light barriers; the browser scenarios call none of the pure helpers by name',
+      + 'wedge stays empty, #271 also proves finite ray endpoints, and #275 densely samples every '
+      + 'protected orthogonal strip across Plan, Static, hidden Iso and light barriers; the browser '
+      + 'scenarios call none of the pure helpers by name',
   },
   {
     // #258: the browser sees only the resulting path/caches; it cannot call

scripts/wall-strip-containment.mjs

@@ -0,0 +1,142 @@
+#!/usr/bin/env node
+// External-backup regression probe for issue #275.
+//
+// Build test-build first (`npx tsc -p tsconfig.test.json` plus fix-test-build),
+// then pass one or more plan-only backups. The files are read locally; their
+// contents are never copied into the repository or printed.
+
+import { createHash } from 'node:crypto';
+import { readFileSync } from 'node:fs';
+
+import { difference } from 'polyclip-ts';
+
+import {
+  canonicalizeConfigGeometry,
+  canonicalizeLayoutGeometry,
+} from '../test-build/coordinate-canonicalization.js';
+import { optimizePlans } from '../test-build/plan-optimizer.js';
+import { prepareSpacePhysicalGeometryInputs } from '../test-build/plan-geometry-preflight.js';
+import { geometryArea } from '../test-build/physical-geometry.js';
+import { spaceModels } from '../test-build/space-geometry.js';
+import {
+  buildMultiWallNodeMap,
+  multiWallProtectedRayIndexes,
+  multiWallProtectedStripGeometry,
+  wallBodiesGeometry,
+  wallIntervals,
+} from '../test-build/wall-thickness.js';
+
+const AREA_EPSILON = 1e-5;
+
+const payloadOf = (backup) => {
+  const payload = backup?.payload && typeof backup.payload === 'object'
+    ? backup.payload
+    : backup;
+  const config = payload?.config && typeof payload.config === 'object'
+    ? payload.config
+    : payload;
+  const layout = payload?.layout && typeof payload.layout === 'object'
+    ? payload.layout
+    : {};
+  if (!config || !Array.isArray(config.spaces)) {
+    throw new Error('input has no config.spaces');
+  }
+  return { config, layout };
+};
+
+const inspectConfig = (config) => {
+  const before = JSON.stringify(config);
+  const models = spaceModels(config);
+  const spaces = [];
+  for (let index = 0; index < config.spaces.length; index++) {
+    const input = prepareSpacePhysicalGeometryInputs(config.spaces[index], models[index]);
+    const geometry = wallBodiesGeometry(
+      input.space.rooms,
+      input.walls,
+      input.openCuts,
+      input.roomOpenings,
+      input.wallKeyPitch,
+      input.cellCm,
+      input.gridPitch,
+      input.coordScale,
+      input.physicalBodies,
+    );
+    if (!geometry) throw new Error(`space ${index}: production wall geometry is null`);
+    const map = buildMultiWallNodeMap(
+      wallIntervals(
+        input.space.rooms,
+        input.walls,
+        input.openCuts,
+        input.wallKeyPitch,
+        input.cellCm,
+        input.gridPitch,
+        input.coordScale,
+      ),
+      input.wallKeyPitch * input.coordScale * 0.04 * 4,
+      input.coordScale,
+    );
+    const nodes = [];
+    for (const node of map.nodes) {
+      const protectedRays = multiWallProtectedRayIndexes(node);
+      if (!protectedRays.length) continue;
+      const required = multiWallProtectedStripGeometry(node, map);
+      if (!required) throw new Error(`space ${index}: protected node has no strip geometry`);
+      const roomMissingArea = geometryArea(difference(required, geometry.roomGeom));
+      const paperMissingArea = geometryArea(difference(required, geometry.paperGeom));
+      nodes.push({
+        point: node.point.map((value) => value / input.coordScale),
+        rays: node.rays.length,
+        protectedRays: protectedRays.length,
+        roomMissingArea,
+        paperMissingArea,
+        pass: roomMissingArea <= AREA_EPSILON && paperMissingArea <= AREA_EPSILON,
+      });
+    }
+    spaces.push({
+      index,
+      degree3Nodes: map.nodes.length,
+      protectedNodes: nodes.length,
+      violations: nodes.filter((node) => !node.pass),
+    });
+  }
+  if (JSON.stringify(config) !== before) throw new Error('geometry inspection mutated config');
+  return {
+    spaces,
+    violations: spaces.reduce((total, space) => total + space.violations.length, 0),
+  };
+};
+
+const inspectBackup = (path) => {
+  const source = readFileSync(path);
+  const backup = JSON.parse(source.toString('utf8'));
+  const raw = payloadOf(backup);
+  const optimized = optimizePlans(raw.config, raw.layout);
+  const applied = {
+    config: canonicalizeConfigGeometry(optimized.config),
+    layout: canonicalizeLayoutGeometry(optimized.layout),
+  };
+  const reloaded = JSON.parse(JSON.stringify(applied));
+  const states = {
+    raw: inspectConfig(raw.config),
+    preview: inspectConfig(optimized.config),
+    applied: inspectConfig(applied.config),
+    reloaded: inspectConfig(reloaded.config),
+  };
+  return {
+    file: path,
+    sha256: createHash('sha256').update(source).digest('hex'),
+    optimizeChanged: optimized.changed,
+    states,
+    pass: Object.values(states).every((state) => state.violations === 0),
+  };
+};
+
+const paths = process.argv.slice(2);
+if (!paths.length) {
+  console.error('usage: node scripts/wall-strip-containment.mjs <backup.json> [...]');
+  process.exit(2);
+}
+
+const report = paths.map(inspectBackup);
+console.log(JSON.stringify({ issue: 275, areaEpsilon: AREA_EPSILON, report }, null, 2));
+if (report.some((entry) => !entry.pass)) process.exitCode = 1;