Fix cross-model queue items being misrepresented and editable into a broken state (#671)

The edit dialog offered a printer picker and target-model dropdown for
an item with alternatives. Saving left a row with variants AND a
printer_id, and the scheduler's fixed-printer branch wins that race, so
it dispatched a row whose library_file_id is still null and failed in
the upload. PATCH now refuses printer/model changes on such an item —
comparing against the current value, since the dialog re-sends
target_model unchanged — and the route eager-loads variants, without
which the guard could not see them and every PATCH response dropped the
alternatives from its payload.

Names come from a shared helper now. A cross-model item holds neither
archive_id nor library_file_id until dispatch, so five separate inlined
fallbacks all rendered "File #null"; they now read "x1c.gcode.3mf +1
more".

The queue also grouped these under "Any H2D" — the first candidate
mirrored onto the row — filing a job under a printer it might never run
on. It groups as "Any H2D / X1C", matching the row beneath it.

frontend/src/components/PrintModal/VariantCandidates.tsx

@@ -17,6 +17,11 @@ interface VariantCandidatesProps {
   /** file id -> chosen plate, for the multi-plate candidates only. */
   plateByFile: Record<number, number | null>;
   onPlateChange: (fileId: number, plateId: number | null) => void;
+  /** Show the set without offering to change it — the edit-queue-item case,
+   *  where reordering would need a variant-level API that doesn't exist. */
+  readOnly?: boolean;
+  /** Replaces the help line under the heading when read-only. */
+  readOnlyNote?: string;
 }
 
 /**
@@ -40,15 +45,21 @@ export function VariantCandidates({
   onReorder,
   plateByFile,
   onPlateChange,
+  readOnly = false,
+  readOnlyNote,
 }: VariantCandidatesProps) {
   const { t } = useTranslation();
 
   const plateQueries = useQueries({
-    queries: candidates.map((c) => ({
-      queryKey: ['library-file-plates', c.id],
-      queryFn: () => api.getLibraryFilePlates(c.id),
-      staleTime: 60_000,
-    })),
+    // Read-only mode shows a job that is already queued — its plates were
+    // chosen when it was created, so there is nothing to fetch or offer.
+    queries: readOnly
+      ? []
+      : candidates.map((c) => ({
+          queryKey: ['library-file-plates', c.id],
+          queryFn: () => api.getLibraryFilePlates(c.id),
+          staleTime: 60_000,
+        })),
   });
 
   const platesByFile = useMemo(() => {
@@ -76,7 +87,9 @@ export function VariantCandidates({
         <PrinterIcon className="w-4 h-4 text-bambu-gray" />
         <span className="text-sm text-bambu-gray">{t('printModal.variants.title')}</span>
       </div>
-      <p className="text-xs text-bambu-gray mb-2">{t('printModal.variants.help')}</p>
+      <p className="text-xs text-bambu-gray mb-2">
+        {readOnly ? (readOnlyNote ?? t('printModal.variants.help')) : t('printModal.variants.help')}
+      </p>
 
       <div className="space-y-2">
         {candidates.map((candidate, index) => {
@@ -116,26 +129,28 @@ export function VariantCandidates({
                 </label>
               )}
 
-              <div className="flex items-center gap-1 shrink-0">
-                <button
-                  type="button"
-                  onClick={() => move(index, index - 1)}
-                  disabled={index === 0}
-                  className="p-1 rounded text-bambu-gray hover:text-white disabled:opacity-30"
-                  aria-label={t('printModal.variants.moveUp')}
-                >
-                  <ArrowUp className="w-3.5 h-3.5" />
-                </button>
-                <button
-                  type="button"
-                  onClick={() => move(index, index + 1)}
-                  disabled={index === candidates.length - 1}
-                  className="p-1 rounded text-bambu-gray hover:text-white disabled:opacity-30"
-                  aria-label={t('printModal.variants.moveDown')}
-                >
-                  <ArrowDown className="w-3.5 h-3.5" />
-                </button>
-              </div>
+              {!readOnly && (
+                <div className="flex items-center gap-1 shrink-0">
+                  <button
+                    type="button"
+                    onClick={() => move(index, index - 1)}
+                    disabled={index === 0}
+                    className="p-1 rounded text-bambu-gray hover:text-white disabled:opacity-30"
+                    aria-label={t('printModal.variants.moveUp')}
+                  >
+                    <ArrowUp className="w-3.5 h-3.5" />
+                  </button>
+                  <button
+                    type="button"
+                    onClick={() => move(index, index + 1)}
+                    disabled={index === candidates.length - 1}
+                    className="p-1 rounded text-bambu-gray hover:text-white disabled:opacity-30"
+                    aria-label={t('printModal.variants.moveDown')}
+                  >
+                    <ArrowDown className="w-3.5 h-3.5" />
+                  </button>
+                </div>
+              )}
             </div>
           );
         })}

frontend/src/components/PrintModal/index.tsx

@@ -73,6 +73,21 @@ export function PrintModal({
   // Cross-model alternatives (#671). One candidate is not a choice, so a
   // single-entry list behaves exactly like an ordinary print.
   const isCrossModel = mode === 'create' && (variantFiles?.length ?? 0) > 1;
+  // Editing an already-queued cross-model item. The candidates are shown so the
+  // dialog doesn't misrepresent the job as a plain "Any H2D" — which is what it
+  // did before, offering a printer picker whose Save would have left a row with
+  // both variants and a printer_id. They are not editable here: changing the
+  // set after queueing needs a variant-level API that doesn't exist, and the
+  // backend refuses the printer/model change either way.
+  const editingVariants: VariantCandidate[] =
+    mode === 'edit-queue-item' && (queueItem?.variants?.length ?? 0) > 1
+      ? queueItem!.variants!.map((v) => ({
+          id: v.library_file_id,
+          filename: v.filename,
+          sliced_for_model: v.target_model,
+        }))
+      : [];
+  const hasEditingVariants = editingVariants.length > 0;
   const [candidates, setCandidates] = useState<VariantCandidate[]>(variantFiles ?? []);
   const [candidatePlates, setCandidatePlates] = useState<Record<number, number | null>>({});
 
@@ -398,6 +413,42 @@ export function PrintModal({
     enabled: assignmentMode === 'model' && !!targetModel,
   });
 
+  // A cross-model job (#671) has no single target model, so the query above is
+  // disabled and the override UI would silently vanish — leaving less control
+  // than the ordinary "Any X1C" flow offers. Ask each candidate's model instead
+  // and offer the union: the job can land on any of them, so anything loaded on
+  // any of them is a legitimate choice. Picking one only some models have is
+  // allowed and meaningful — it narrows which candidates can match.
+  const candidateModels = useMemo(
+    () => Array.from(new Set(candidates.map((c) => c.sliced_for_model).filter((m): m is string => !!m))),
+    [candidates],
+  );
+  const candidateFilamentQueries = useQueries({
+    queries: isCrossModel
+      ? candidateModels.map((model) => ({
+          queryKey: ['available-filaments', model, targetLocation],
+          queryFn: () => api.getAvailableFilaments(model, targetLocation ?? undefined),
+        }))
+      : [],
+  });
+  const crossModelFilaments = useMemo(() => {
+    const seen = new Set<string>();
+    const merged: NonNullable<typeof availableFilaments> = [];
+    for (const query of candidateFilamentQueries) {
+      for (const filament of query.data ?? []) {
+        // Same type+colour loaded on two models is one choice, not two.
+        const key = `${filament.type}|${filament.color}|${filament.tray_info_idx}`;
+        if (!seen.has(key)) {
+          seen.add(key);
+          merged.push(filament);
+        }
+      }
+    }
+    return merged;
+  }, [candidateFilamentQueries]);
+
+  const effectiveAvailableFilaments = isCrossModel ? crossModelFilaments : availableFilaments;
+
   // Only fetch printer status when single printer selected (for filament mapping)
   const { data: printerStatus, isLoading: printerStatusLoading } = useQuery({
     queryKey: ['printer-status', effectivePrinterId],
@@ -1261,8 +1312,13 @@ export function PrintModal({
   // is the filament each slot must be printed in, which the scheduler matches
   // against whatever printer of the model it picks. Needs the model's loaded
   // filaments to offer as alternatives.
+  // Cross-model items have no targetModel by design — their candidates each
+  // carry their own — so gate on having somewhere to source choices from.
   const showFilamentOverride =
-    assignmentMode === 'model' && !!targetModel && !!availableFilaments && availableFilaments.length > 0;
+    assignmentMode === 'model'
+    && (isCrossModel || !!targetModel)
+    && !!effectiveAvailableFilaments
+    && effectiveAvailableFilaments.length > 0;
 
   // Dual-nozzle gate for the Nozzle Offset Calibration toggle (#1682).
   // Mirrors backend `DUAL_NOZZLE_MODELS` so model-based assignment can show
@@ -1371,8 +1427,19 @@ export function PrintModal({
               />
             )}
 
+            {hasEditingVariants && (
+              <VariantCandidates
+                candidates={editingVariants}
+                readOnly
+                readOnlyNote={t('printModal.variants.editNote')}
+                onReorder={() => {}}
+                plateByFile={{}}
+                onPlateChange={() => {}}
+              />
+            )}
+
             {/* Printer selection with per-printer mapping — hidden when printer is pre-selected via props */}
-            {!isCrossModel && !initialSelectedPrinterIds?.length && (
+            {!isCrossModel && !hasEditingVariants && !initialSelectedPrinterIds?.length && (
               <PrinterSelector
                 printers={printers || []}
                 selectedPrinterIds={selectedPrinters}
@@ -1404,7 +1471,7 @@ export function PrintModal({
             {showFilamentOverride && !isMultiPlateSelection && effectiveFilamentReqs && (
               <FilamentOverride
                 filamentReqs={effectiveFilamentReqs}
-                availableFilaments={availableFilaments!}
+                availableFilaments={effectiveAvailableFilaments!}
                 overrides={filamentOverrides}
                 onChange={setFilamentOverrides}
                 forceColorMatch={forceColorMatch}