fix: harden mesh check against bad indices and tidy review follow-ups

- Reject triangle indices outside the vertex list instead of stalling the queue
- Leave degenerate triangles out of body bounding boxes
- Skip the quality fetch without a print id and never show a previous print's result
- Disable the per-check switches while a save is in flight

backend/src/services/meshQuality.ts

@@ -112,11 +112,17 @@ export function analyzeMesh(vertices: ArrayLike<number>, triangles?: ArrayLike<n
   const firstVertex = new Uint32Array(vertexCount);
   for (let v = ids.length - 1; v >= 0; v--) firstVertex[ids[v]] = v;
   const position = (id: number, axis: number) => vertices[firstVertex[id] * 3 + axis];
+  // Degenerate faces join no body, so they mustn't make a bounding box of their own either.
+  const skipped = new Uint8Array(triangleCount);
 
   for (let t = 0; t < triangleCount; t++) {
     const a = corner(t * 3);
     const b = corner(t * 3 + 1);
     const c = corner(t * 3 + 2);
+    // An index past the vertex list would make NaN edge keys, which never group and stall the loop below.
+    if (a === undefined || b === undefined || c === undefined) {
+      throw new RangeError("Triangle index outside the vertex list");
+    }
     const ax = position(a, 0);
     const ay = position(a, 1);
     const az = position(a, 2);
@@ -131,6 +137,7 @@ export function analyzeMesh(vertices: ArrayLike<number>, triangles?: ArrayLike<n
     const nz = ux * vy - uy * vx;
     if (a === b || b === c || a === c || nx * nx + ny * ny + nz * nz <= degenerateArea * degenerateArea) {
       degenerate++;
+      skipped[t] = 1;
       continue;
     }
     // The tetrahedron to the origin; the sum over a closed surface is its volume.
@@ -172,6 +179,7 @@ export function analyzeMesh(vertices: ArrayLike<number>, triangles?: ArrayLike<n
   // Each body's bounding box, keyed by its root vertex.
   const boxes = new Map<number, number[]>();
   for (let t = 0; t < triangleCount; t++) {
+    if (skipped[t]) continue;
     for (let k = 0; k < 3; k++) {
       const id = corner(t * 3 + k);
       const root = findRoot(parent, id);

backend/tests/meshQuality.test.ts

@@ -75,7 +75,11 @@ describe("analyzeMesh", () => {
   it("counts degenerate triangles without treating them as holes", () => {
     const sliver = [0, 0, 0, 5, 0, 0, 10, 0, 0];
     const stats = analyzeMesh(soup([...box(), sliver]));
-    expect(stats).toMatchObject({ degenerateTriangles: 1, openEdges: 0 });
+    expect(stats).toMatchObject({ degenerateTriangles: 1, openEdges: 0, shells: 1, fragments: 0 });
+  });
+
+  it("rejects a triangle index outside the vertex list", () => {
+    expect(() => analyzeMesh([0, 0, 0, 1, 0, 0, 0, 1, 0], [0, 1, 3])).toThrow(RangeError);
   });
 
   it("tells a stray fragment from a second part", () => {

frontend/src/pages/ModelDetailPage/QualityCheck/useQualityCheck.ts

@@ -14,8 +14,9 @@ export type QualityOutcome = "good" | "issues" | null;
 export function useQualityCheck(printId: string, onUnauthorized?: () => void) {
   const { t } = useTranslation("models");
   const showToast = useToast();
-  const [quality, setQuality] = useState<PrintQuality | null>(null);
-  const [outcome, setOutcome] = useState<QualityOutcome>(null);
+  // Tagged with their print, so a newly opened model never shows the last one's result for a render.
+  const [quality, setQuality] = useState<{ printId: string; value: PrintQuality } | null>(null);
+  const [outcome, setOutcome] = useState<{ printId: string; value: QualityOutcome } | null>(null);
   // Kept out of the effect's deps: a new toast function or translation mustn't restart a running check.
   const notify = useRef({ showToast, t, onUnauthorized });
   useEffect(() => {
@@ -23,19 +24,20 @@ export function useQualityCheck(printId: string, onUnauthorized?: () => void) {
   }, [showToast, t, onUnauthorized]);
 
   useEffect(() => {
+    if (!printId) return;
     let cancelled = false;
     let timer: ReturnType<typeof setTimeout> | undefined;
     setQuality(null);
     setOutcome(null);
 
     const settle = (next: PrintQuality, watched: boolean) => {
-      setQuality(next);
+      setQuality({ printId, value: next });
       if (next.status === "checking") {
         timer = setTimeout(() => void poll(), POLL_MS);
         return;
       }
       if (!watched || (next.status !== "good" && next.status !== "issues")) return;
-      setOutcome(next.status);
+      setOutcome({ printId, value: next.status });
       if (next.status === "issues") {
         // Only minor problems, which slicers usually cope with: a note rather than a warning.
         const minor = worstSeverity(next) === "minor";
@@ -78,5 +80,8 @@ export function useQualityCheck(printId: string, onUnauthorized?: () => void) {
     };
   }, [printId]);
 
-  return { quality, outcome };
+  return {
+    quality: quality?.printId === printId ? quality.value : null,
+    outcome: outcome?.printId === printId ? outcome.value : null,
+  };
 }

frontend/src/pages/RenderingPage/QualityChecksDialog.tsx

@@ -18,10 +18,12 @@ type Props = {
   checksOff: QualityCheckKey[];
   onChange: (checksOff: QualityCheckKey[]) => void;
   onClose: () => void;
+  /** While a save is in flight, so overlapping saves can't land out of order. */
+  disabled?: boolean;
 };
 
 /** One switch per kind of print problem. Each saves as soon as it's switched. */
-export default function QualityChecksDialog({ open, checksOff, onChange, onClose }: Props) {
+export default function QualityChecksDialog({ open, checksOff, onChange, onClose, disabled }: Props) {
   const { t } = useTranslation(["app", "common"]);
   const toggle = (key: QualityCheckKey, on: boolean) =>
     onChange(on ? checksOff.filter((off) => off !== key) : [...checksOff, key]);
@@ -52,6 +54,7 @@ export default function QualityChecksDialog({ open, checksOff, onChange, onClose
                 </Box>
                 <Switch
                   checked={!checksOff.includes(key)}
+                  disabled={disabled}
                   onChange={(e) => toggle(key, e.target.checked)}
                   slotProps={{ input: { "aria-labelledby": titleId } }}
                 />

frontend/src/pages/RenderingPage/QualityChecksSection.tsx

@@ -149,6 +149,7 @@ export default function QualityChecksSection({ onUnauthorized }: Props) {
         <QualityChecksDialog
           open={checksOpen}
           checksOff={settings.checks_off}
+          disabled={saving}
           onChange={(checksOff) => void save({ checks_off: checksOff })}
           onClose={() => setChecksOpen(false)}
         />