feat: add architectural snap overlay

Issue: #137
User-Visible: yes

demo/performance/README.md

@@ -12,6 +12,16 @@ flat while reporting the same profile. The dedicated
 plus absolute noise/ceiling checks. Only the exact-SHA Linux workflow is gate
 evidence; a local report is diagnostic.
 
+Issue #137 adds `large-house-plan-snap-v1` without changing the meaning or
+budgets of the original profile. The same 60-room/60-partition fixture gains
+six saved open outlines, renders the Plan snap overlay, and sends 120 real
+pointer moves across endpoint, line and miss targets. Candidate bundles fail
+inside the runner if the static DOM or geometry cache grows, more than one
+active node appears, endpoint/line paths are not both exercised, or config and
+websocket traffic change. Its dedicated budget retains every original timing,
+heap and cache ceiling and adds the measured pointer series plus a one-entry
+snap-geometry cache cap. Exact-SHA Linux output is the only gate evidence.
+
 The runner records seven measured samples after one discarded warm-up. With
 this intentionally small CI sample, the nearest-rank `p95` is the observed
 maximum; reports keep the conventional field name but should be read as a
@@ -110,6 +120,7 @@ Build and copy a fresh demo bundle first, then run:
 
 ```bash
 npm run benchmark:large-house -- --samples=7 --warmups=1 --output=artifacts/performance/local.json
+npm run benchmark:large-house-plan-snap -- --samples=7 --warmups=1 --output=artifacts/performance/plan-snap-local.json
 ```
 
 A local report is diagnostic only; it cannot replace the CI comparison.

demo/performance/budgets-large-house-plan-snap.json

@@ -0,0 +1,95 @@
+{
+  "schema": 1,
+  "profile": "large-house-plan-snap-v1",
+  "minimumSamples": 7,
+  "timings": {
+    "modelReadyMs": {
+      "stat": "median",
+      "maxRegressionRatio": 0.3,
+      "noiseAllowanceMs": 200,
+      "hardMaxMs": 2500
+    },
+    "firstStableRenderMs": {
+      "stat": "median",
+      "maxRegressionRatio": 0.3,
+      "noiseAllowanceMs": 250,
+      "hardMaxMs": 3000
+    },
+    "planSnapPointerMs": {
+      "stat": "median",
+      "maxRegressionRatio": 0.5,
+      "noiseAllowanceMs": 250,
+      "hardMaxMs": 5000
+    },
+    "spaceSwitchMs": {
+      "stat": "median",
+      "maxRegressionRatio": 0.5,
+      "noiseAllowanceMs": 75,
+      "hardMaxMs": 1500
+    },
+    "stateUpdateMs": {
+      "stat": "median",
+      "maxRegressionRatio": 0.5,
+      "noiseAllowanceMs": 75,
+      "hardMaxMs": 1000
+    },
+    "resizePreviewMs": {
+      "stat": "median",
+      "maxRegressionRatio": 0.4,
+      "noiseAllowanceMs": 150,
+      "hardMaxMs": 2000
+    },
+    "panZoomMs": {
+      "stat": "median",
+      "maxRegressionRatio": 0.5,
+      "noiseAllowanceMs": 60,
+      "hardMaxMs": 500
+    },
+    "settingsDialogMs": {
+      "stat": "median",
+      "maxRegressionRatio": 0.5,
+      "noiseAllowanceMs": 100,
+      "hardMaxMs": 1000
+    },
+    "switchCycleMs": {
+      "stat": "median",
+      "maxRegressionRatio": 0.35,
+      "noiseAllowanceMs": 250,
+      "hardMaxMs": 7000
+    }
+  },
+  "longTasks": {
+    "maxSingleMs": 3000,
+    "maxSingleRegressionRatio": 0.3,
+    "maxSingleNoiseAllowanceMs": 250,
+    "maxCountP95": 30,
+    "maxCountRegressionRatio": 0.35,
+    "countNoiseAllowance": 3,
+    "maxTotalP95Ms": 12000,
+    "maxTotalRegressionRatio": 0.3,
+    "noiseAllowanceMs": 150
+  },
+  "heap": {
+    "required": true,
+    "hardMaxGrowthBytes": 67108864,
+    "maxRegressionRatio": 0.75,
+    "noiseAllowanceBytes": 16777216
+  },
+  "cacheEntries": {
+    "cleanFloor": 160,
+    "glowClip": 200,
+    "wallUnion": 1,
+    "openingTunnel": 1,
+    "openingWallIndex": 1,
+    "planSnapGeometry": 1
+  },
+  "cacheGrowth": {
+    "cleanFloor": 0,
+    "glowClip": 0,
+    "wallUnion": 0,
+    "openingTunnel": 0,
+    "openingWallIndex": 0,
+    "planSnapGeometry": 0
+  },
+  "renderedDevices": 200
+}

demo/performance/card-contract.mjs

@@ -33,13 +33,15 @@ export const LARGE_HOUSE_CARD_CONTRACT = Object.freeze({
     '_gridPitch',
     '_loadOk',
     '_model',
+    '_path',
     '_rszDrag',
+    '_serverCfg',
     '_settingsDialog',
     '_tool',
   ]),
   // A comparison SHA before #89 is intentionally flat; the isometric runner
   // checks these two members only when the target source tree supports Stage 1.
-  optionalFields: Object.freeze(['_isoGeometryCache', '_setProjection']),
+  optionalFields: Object.freeze(['_isoGeometryCache', '_planSnapGeometryCache', '_setProjection']),
   fieldTypes: Object.freeze({
     _booting: 'boolean',
     _cleanFloorCache: 'map',
@@ -48,8 +50,11 @@ export const LARGE_HOUSE_CARD_CONTRACT = Object.freeze({
     _gridPitch: 'number',
     _loadOk: 'boolean',
     _model: 'array',
+    _path: 'array',
     _isoGeometryCache: 'map',
+    _planSnapGeometryCache: 'object',
     _setProjection: 'function',
+    _serverCfg: 'object',
     _tool: 'string',
   }),
 });