fix(queue): enforce sliced-model compatibility on cross-model dispatch (#2578)

A queue item's "Any <model>" button labeled itself from the file's slice
metadata while the scheduler used the row's target_model, so an X1C-sliced
item targeting H2D showed "Any X1C" above "assign to first idle H2D". The
mismatch itself was created silently: sliced-for metadata loads async, and
switching to model mode before it arrived pre-selected the alphabetically
first model (H2D on a mixed farm), after which the model dropdown hid
itself. Nothing validated compatibility, so the scheduler would hand X1C
G-code to an H2D.

Frontend: never default the target silently, keep the dropdown visible in
model mode (incompatible models disabled), label from the actual target,
warn on mismatch, block submit when incompatible.

Backend: new GCODE_COMPAT_FAMILIES table (X1/X1C/X1E/P1P/P1S interchange;
everything else exact-match; missing metadata never blocks). Queue create
and update reject incompatible targets with 400; the scheduler holds back
pre-existing mismatched rows with an actionable waiting_reason instead of
dispatching them.

frontend/src/components/PrintModal/PrinterSelector.tsx

@@ -13,6 +13,7 @@ import {
 } from 'lucide-react';
 import { api, type PrinterStatus } from '../../api/client';
 import { getColorName } from '../../utils/colors';
+import { isGcodeCompatible } from '../../utils/printer';
 import {
   normalizeColorForCompare,
   colorsAreSimilar,
@@ -409,10 +410,15 @@ export function PrinterSelector({
             onClick={() => {
               onAssignmentModeChange!('model');
               onMultiSelect([]);
-              // Pre-select the sliced-for model if available, otherwise first model
+              // Pre-select the sliced-for model when it has printers. NEVER
+              // silently fall back to another model (#2578): uniqueModels is
+              // alphabetically sorted, so the old `uniqueModels[0]` default
+              // quietly targeted e.g. H2D for an X1C-sliced file whenever the
+              // metadata hadn't loaded yet. Leave it unset and let the user
+              // pick from the dropdown instead.
               const defaultModel = slicedForModel && uniqueModels.includes(slicedForModel)
                 ? slicedForModel
-                : uniqueModels[0];
+                : null;
               onTargetModelChange!(defaultModel);
             }}
             className={`flex-1 flex items-center justify-center gap-2 px-3 py-2 rounded-lg border transition-colors ${
@@ -422,7 +428,12 @@ export function PrinterSelector({
             }`}
           >
             <Users className="w-4 h-4" />
-            <span className="text-sm">Any {slicedForModel || 'Model'}</span>
+            {/* In model mode the label must reflect the ACTUAL scheduler
+                target, not the slice metadata — an edited queue item can
+                target a different model than the file was sliced for (#2578). */}
+            <span className="text-sm">
+              Any {(assignmentMode === 'model' ? targetModel : null) || slicedForModel || 'Model'}
+            </span>
           </button>
         </div>
       )}
@@ -430,29 +441,58 @@ export function PrinterSelector({
       {/* Model selection and location filter (when in model mode) */}
       {assignmentMode === 'model' && modelAssignmentAvailable && (
         <div className="space-y-3 mb-4">
-          {/* Model selector — only show when sliced model is unknown */}
-          {!slicedForModel && (
-            <div>
-              <label className="block text-xs text-bambu-gray mb-1">Target Model</label>
-              <select
-                value={targetModel || ''}
-                onChange={(e) => {
-                  onTargetModelChange!(e.target.value || null);
-                  // Clear location when model changes
-                  if (onTargetLocationChange) {
-                    onTargetLocationChange(null);
-                  }
-                }}
-                className="w-full px-3 py-2 bg-bambu-dark border border-bambu-dark-tertiary rounded-lg text-white focus:border-bambu-green focus:outline-none text-sm"
-              >
-                <option value="">Select a model...</option>
-                {uniqueModels.map((model) => (
-                  <option key={model} value={model}>
+          {/* Model selector — always visible in model mode so a wrong target
+              on an existing queue item can be seen and fixed (#2578).
+              Incompatible models are disabled: G-code sliced for one model
+              must only go to that model or its interchange family. */}
+          <div>
+            <label className="block text-xs text-bambu-gray mb-1">
+              Target Model
+              {slicedForModel && <span className="ml-2 text-bambu-gray/70">(sliced for {slicedForModel})</span>}
+            </label>
+            <select
+              value={targetModel || ''}
+              onChange={(e) => {
+                onTargetModelChange!(e.target.value || null);
+                // Clear location when model changes
+                if (onTargetLocationChange) {
+                  onTargetLocationChange(null);
+                }
+              }}
+              className="w-full px-3 py-2 bg-bambu-dark border border-bambu-dark-tertiary rounded-lg text-white focus:border-bambu-green focus:outline-none text-sm"
+            >
+              <option value="">Select a model...</option>
+              {uniqueModels.map((model) => {
+                const compatible = isGcodeCompatible(slicedForModel, model);
+                return (
+                  <option key={model} value={model} disabled={!compatible}>
                     {model}
+                    {!compatible ? ` — incompatible with ${slicedForModel} G-code` : ''}
                   </option>
-                ))}
-              </select>
-            </div>
+                );
+              })}
+            </select>
+          </div>
+
+          {/* Cross-model state on an existing row: same file/target mismatch
+              the specific-printer path already warns about (#2578). */}
+          {slicedForModel && targetModel && targetModel !== slicedForModel && (
+            isGcodeCompatible(slicedForModel, targetModel) ? (
+              <div className="p-3 bg-yellow-50 dark:bg-yellow-500/10 border border-yellow-300 dark:border-yellow-500/30 rounded-lg flex items-center gap-2">
+                <AlertTriangle className="w-4 h-4 text-yellow-600 dark:text-yellow-400 flex-shrink-0" />
+                <span className="text-sm text-yellow-700 dark:text-yellow-400">
+                  File was sliced for {slicedForModel}, but will be dispatched to a {targetModel} printer
+                </span>
+              </div>
+            ) : (
+              <div className="p-3 bg-red-50 dark:bg-red-500/10 border border-red-300 dark:border-red-500/30 rounded-lg flex items-center gap-2">
+                <AlertCircle className="w-4 h-4 text-red-600 dark:text-red-400 flex-shrink-0" />
+                <span className="text-sm text-red-700 dark:text-red-400">
+                  File was sliced for {slicedForModel} and cannot be dispatched to {targetModel} printers —
+                  select a compatible model
+                </span>
+              </div>
+            )
           )}
 
           {/* Location filter (only show when target model is selected and locations exist) */}

frontend/src/components/PrintModal/index.tsx

@@ -17,6 +17,7 @@ import {
 } from '../../hooks/useFilamentMapping';
 import { useMultiPrinterFilamentMapping, type PerPrinterConfig } from '../../hooks/useMultiPrinterFilamentMapping';
 import { getColorName } from '../../utils/colors';
+import { isGcodeCompatible } from '../../utils/printer';
 import { getCurrencySymbol } from '../../utils/currency';
 import { getBedTypeInfo } from '../../utils/bedType';
 import { toDateTimeLocalValue, parseUTCDate } from '../../utils/date';
@@ -576,6 +577,17 @@ export function PrintModal({
     }
   }, [targetModel, selectedPlate, prevTargetModel, prevPlateForOverrides, mode]);
 
+  // The sliced-for metadata loads async. If the user switched to model mode
+  // before it arrived, the target is still empty (we never silently default
+  // to another model, #2578) — fill it with the sliced-for model once known,
+  // provided an active printer of that model exists.
+  useEffect(() => {
+    if (assignmentMode !== 'model' || targetModel || !slicedForModel) return;
+    if (printers?.some((p) => p.is_active && p.model === slicedForModel)) {
+      setTargetModel(slicedForModel);
+    }
+  }, [assignmentMode, targetModel, slicedForModel, printers]);
+
   // Auto-expand per-printer mapping when setting is enabled and multiple printers selected
   // Only applies once per printer on initial selection, not when user unchecks
   useEffect(() => {
@@ -781,6 +793,12 @@ export function PrintModal({
       showToast('Please select a target printer model', 'error');
       return;
     }
+    // Cross-model safety gate (#2578) — mirrors the backend's 400 so the user
+    // gets inline feedback instead of a failed request.
+    if (assignmentMode === 'model' && !isGcodeCompatible(slicedForModel, targetModel)) {
+      showToast(`File was sliced for ${slicedForModel} and cannot be dispatched to ${targetModel} printers`, 'error');
+      return;
+    }
 
     setIsSubmitting(true);
     // Calculate total API calls: plates × printers (or 1 for model-based)
@@ -1070,6 +1088,8 @@ export function PrintModal({
     // Need valid printer/model selection
     if (assignmentMode === 'printer' && selectedPrinters.length === 0) return false;
     if (assignmentMode === 'model' && !targetModel) return false;
+    // Cross-model mismatch cannot be queued (#2578)
+    if (assignmentMode === 'model' && !isGcodeCompatible(slicedForModel, targetModel)) return false;
 
     // For multi-plate files, need at least one plate selected
     if (isMultiPlate && selectedPlates.size === 0) return false;
@@ -1085,6 +1105,7 @@ export function PrintModal({
     selectedPrinters.length,
     assignmentMode,
     targetModel,
+    slicedForModel,
     isMultiPlate,
     selectedPlates.size,
     isPending,