perf/fix v1.43.1: external audit P1 — render cost, drag threshold, geometry, backend

L1: memoized space model + open pairs (structural fingerprint key, epoch
bumped synchronously at mutation time, not inside the debounce); hoisted
per-room geometry out of the render loop; smoke asserts zero recomputation
across state pushes.

L4: openings get the 3 px drag threshold used by every other pipeline and
only write when the geometry actually changed — taps open the dialog again.

G2: interiorPoint() replaces the vertex mean, so island rooms inside
concave (U/L) parents are accepted and their evenodd holes render; traced
duplicates still are not containment.

G3: segKey rounds before ordering — one shared wall, one key.

B2: _check_write fails closed when the entry is unavailable.
B3: layout/set honours expected_rev and returns the new rev.
B4: config/set without expected_rev over a non-empty store logs a warning.
B5: coordinates reject NaN/Infinity; spaces/rooms/markers/decor/layout capped.

+2 unit tests (118), +2 backend tests (14), smoke_render_perf; docs
same-commit

src/logic.ts

@@ -38,8 +38,14 @@ export function formatLength(cm: number, imperial: boolean): string {
  * normalized (0..1) coordinates need more (see roomEdges).
  */
 export function segKey(a: number[], b: number[], prec = 1): string {
-  const [p, q] = a[0] < b[0] || (a[0] === b[0] && a[1] <= b[1]) ? [a, b] : [b, a];
-  return `${p[0].toFixed(prec)},${p[1].toFixed(prec)}-${q[0].toFixed(prec)},${q[1].toFixed(prec)}`;
+  // audit G3: ROUND FIRST, then order. Ordering on raw floats while printing
+  // rounded ones let one wall produce two different keys, so shared walls were
+  // emitted twice and the dedup invariant quietly broke.
+  const ax = a[0].toFixed(prec), ay = a[1].toFixed(prec);
+  const bx = b[0].toFixed(prec), by = b[1].toFixed(prec);
+  const first = ax < bx || (ax === bx && ay <= by);
+  const [px, py, qx, qy] = first ? [ax, ay, bx, by] : [bx, by, ax, ay];
+  return `${px},${py}-${qx},${qy}`;
 }
 
 /**
@@ -224,6 +230,36 @@ export function segmentsProperlyCross(
 }
 
 /** Is any area of outline `a` strictly inside `b`? Also catches nested and duplicate outlines. */
+/**
+ * A point guaranteed to lie strictly inside the polygon (audit G2).
+ * The arithmetic mean of the vertices lies OUTSIDE concave shapes (U/L rooms
+ * are common in hand-drawn plans), which made containment tests misfire.
+ * Strategy: try the midpoints of the diagonals from each vertex, then a
+ * triangle centroid of consecutive vertices — the first point that passes
+ * pointStrictlyInside wins.
+ */
+export function interiorPoint(poly: number[][], eps = 1e-6): number[] | null {
+  if (!poly || poly.length < 3) return null;
+  const n = poly.length;
+  const mean = [
+    poly.reduce((s, p) => s + p[0], 0) / n,
+    poly.reduce((s, p) => s + p[1], 0) / n,
+  ];
+  if (pointStrictlyInside(mean, poly, eps)) return mean;
+  for (let i = 0; i < n; i++) {
+    // centroid of the ear at vertex i
+    const a = poly[(i - 1 + n) % n], b = poly[i], c = poly[(i + 1) % n];
+    const cand = [(a[0] + b[0] + c[0]) / 3, (a[1] + b[1] + c[1]) / 3];
+    if (pointStrictlyInside(cand, poly, eps)) return cand;
+  }
+  for (let i = 0; i < n; i++)
+    for (let j = i + 2; j < n; j++) {
+      const cand = [(poly[i][0] + poly[j][0]) / 2, (poly[i][1] + poly[j][1]) / 2];
+      if (pointStrictlyInside(cand, poly, eps)) return cand;
+    }
+  return null;
+}
+
 function coversArea(a: number[][], b: number[][], eps: number): boolean {
   let allOnBoundary = true;
   for (const v of a) {
@@ -232,11 +268,8 @@ function coversArea(a: number[][], b: number[][], eps: number): boolean {
   }
   // every vertex sits on b's outline → a duplicate or traced outline: probe the middle
   if (allOnBoundary) {
-    const c = [
-      a.reduce((s, p) => s + p[0], 0) / a.length,
-      a.reduce((s, p) => s + p[1], 0) / a.length,
-    ];
-    return pointStrictlyInside(c, b, eps);
+    const c = interiorPoint(a, eps); // audit G2: NOT the vertex mean
+    return !!c && pointStrictlyInside(c, b, eps);
   }
   return false;
 }
@@ -250,12 +283,10 @@ export function polyContainsPoly(outer: number[][], inner: number[][], eps = 1e-
         return false;
   for (const v of inner)
     if (!pointStrictlyInside(v, outer, eps) && !pointOnBoundary(v, outer, eps)) return false;
-  // identical/traced outlines are NOT containment — probe the centroid strictness both ways
-  const c = [
-    inner.reduce((s, p) => s + p[0], 0) / inner.length,
-    inner.reduce((s, p) => s + p[1], 0) / inner.length,
-  ];
-  return pointStrictlyInside(c, outer, eps) && polygonArea(inner) < polygonArea(outer) - eps;
+  // identical/traced outlines are NOT containment — probe a real interior point
+  // (audit G2: the vertex mean lies outside concave rooms)
+  const c = interiorPoint(inner, eps);
+  return !!c && pointStrictlyInside(c, outer, eps) && polygonArea(inner) < polygonArea(outer) - eps;
 }
 
 /**