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

tests_backend/test_validation.py

@@ -125,3 +125,18 @@ def test_space_temp_bounds():
         "settings": {"fill_mode": "temp", "temp_min": 19.5, "temp_max": "24"},
     }
     v.SPACE_SCHEMA(ok)
+
+
+def test_finite_coordinates_rejected():
+    """audit B5: NaN/Infinity coordinates must not reach storage."""
+    for bad in ("NaN", "Infinity", "-Infinity", float("nan"), float("inf")):
+        with pytest.raises(vol.Invalid):
+            v.LAYOUT_SCHEMA({"dev1": {"x": bad, "y": 0.5}})
+    assert v.LAYOUT_SCHEMA({"dev1": {"x": 0.5, "y": 0.25}})
+
+
+def test_collection_caps():
+    """audit B5: unbounded collections are capped."""
+    big = {f"d{i}": {"x": 0.1, "y": 0.1} for i in range(v.MAX_LAYOUT + 1)}
+    with pytest.raises(vol.Invalid):
+        v.LAYOUT_SCHEMA(big)