perf: вычитать лестницы из площади пола только по запросу (#669)

Путь чистого пола строят четыре места рендера, а площадь читают только
подсказка комнаты и PDF. cleanFloorForRoom больше не вычитает лестницы при
построении пути: площадь считается при первом чтении и хранится в том же
закэшированном объекте. geometryMinusStairs передаёт в polyclip только
контуры лестниц, чей габарит пересекает вычитаемую геометрию, — результат
тот же, а комната на этаже с 250 лестницами больше не прогоняет все 250.

Issue: #669
User-Visible: no
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018qZfe7YS4rqEMKoVeS3GKd

src/clean-floor.ts

@@ -8,9 +8,12 @@ export type CleanFloorResult = {
   floor: number[][];
   geom: Geom | null;
   path: string;
-  area: number;
+  /** Clean-floor area minus stairs, computed on the first read (#669). */
+  readonly area: number;
 };
 
+type StairAreaFn = (source: Geom, stairs: SpaceModel['stairs'] | undefined) => number;
+
 export function cleanFloorForRoom(input: {
   room: RoomCfg;
   floor: number[][];
@@ -19,6 +22,8 @@ export function cleanFloorForRoom(input: {
   resizePreview: boolean;
   cache: Map<string, CleanFloorResult>;
   physicalBodies(space: SpaceModel): number[][][];
+  /** Test seam (#669): the stair subtraction behind `area`. */
+  areaMinusStairs?: StairAreaFn;
 }): CleanFloorResult {
   const { room, floor, space } = input;
   if (!space) return {
@@ -40,11 +45,21 @@ export function cleanFloorForRoom(input: {
       && Math.max(...by) >= box[1] && Math.min(...by) <= box[3];
   });
   const geom = candidates.length ? floorMinusBodies(floor, candidates) : null;
-  const result = {
+  const subject = (geom || [[[...floor, floor[0]]]]) as Geom;
+  const stairs = space.stairs;
+  const areaMinusStairs: StairAreaFn = input.areaMinusStairs ?? geometryAreaMinusStairs;
+  let area: number | undefined;
+  const result: CleanFloorResult = {
     floor,
     geom,
     path: geom ? polyclipPathD(geom) : '',
-    area: geometryAreaMinusStairs(geom || [[[...floor, floor[0]]]], space.stairs),
+    // #669: four render paths read only `path`; the room tooltip and the PDF
+    // read the area. Subtracting up to 250 stair footprints per room belongs
+    // to that first read, not to every render of the floor.
+    get area() {
+      if (area === undefined) area = areaMinusStairs(subject, stairs);
+      return area;
+    },
   };
   if (!input.resizePreview) lruWrite(input.cache, key, result, 600);
   return result;

src/stairs.ts

@@ -234,7 +234,7 @@ export function geometryAreaMinusStairs(
 export function geometryMinusStairs(
   source: Geom, stairs: readonly Stair[] | null | undefined, scale = NORM_W,
 ): Geom {
-  const footprints = stairList(stairs).map((stair) => stairFootprintGeometry(stair, scale));
+  const footprints = stairFootprintsTouching(source, stairs, scale);
   if (!footprints.length) return source;
   try {
     // A single sweep avoids repeatedly rebuilding the same subject for dense floors.
@@ -249,6 +249,48 @@ export function geometryMinusStairs(
   }
 }
 
+type Bounds = readonly [number, number, number, number];
+
+function geometryBounds(geometry: Geom): Bounds | null {
+  let minX = Infinity;
+  let minY = Infinity;
+  let maxX = -Infinity;
+  let maxY = -Infinity;
+  const visit = (value: unknown): void => {
+    if (!Array.isArray(value)) return;
+    if (typeof value[0] === 'number') {
+      const x = value[0];
+      const y = value[1] as number;
+      if (x < minX) minX = x;
+      if (x > maxX) maxX = x;
+      if (y < minY) minY = y;
+      if (y > maxY) maxY = y;
+      return;
+    }
+    for (const item of value) visit(item);
+  };
+  visit(geometry);
+  return minX <= maxX && minY <= maxY ? [minX, minY, maxX, maxY] : null;
+}
+
+const boundsOverlap = (a: Bounds, b: Bounds | null): boolean => !!b
+  && a[0] <= b[2] && b[0] <= a[2] && a[1] <= b[3] && b[1] <= a[3];
+
+/**
+ * #669: only a footprint whose bounds overlap the subject can change the
+ * difference. A room on a maximum-size floor otherwise sends all 250 stair
+ * footprints into one polyclip sweep, and the room count multiplies it.
+ */
+export function stairFootprintsTouching(
+  source: Geom, stairs: readonly Stair[] | null | undefined, scale = NORM_W,
+): Geom[] {
+  const bounds = geometryBounds(source);
+  if (!bounds) return [];
+  return stairList(stairs)
+    .map((stair) => stairFootprintGeometry(stair, scale))
+    .filter((footprint) => boundsOverlap(bounds, geometryBounds(footprint)));
+}
+
 /**
  * The summary panel calculates floor area after the first paint. A maximum
  * size space may contain 250 stairs; clipping all their footprints in one