fix: constrain scale adjust failover family

app/api/canvas/local-edit/route.ts

@@ -1499,6 +1499,8 @@ export async function POST(request: NextRequest) {
           : undefined,
         scaleAdjustPreferSameNameProviderFailover:
           isScaleAdjustOperation && Boolean(scaleAdjustModelFamily),
+        scaleAdjustStrictSameFamilyFailover:
+          isScaleAdjustOperation && Boolean(scaleAdjustModelFamily),
         manualRegionReferenceImageCount: manualRegionReferenceImageUrls.length,
         regionReferenceImageCount:
           referenceImages.length,

lib/canvas/generate-image.ts

@@ -1737,6 +1737,39 @@ function normalizeModelNameForSimilarity(value: unknown) {
     .replace(/\s+/g, " ");
 }
 
+function resolveCanvasScaleAdjustModelFamilyFromText(value: unknown) {
+  const normalized = normalizeModelNameForSimilarity(value);
+  const compact = normalized.replace(/[^a-z0-9]+/g, "");
+  if (!normalized && !compact) return "";
+  if (
+    normalized.includes("gemini-3-1-flash-image-preview") ||
+    normalized.includes("gemini-3.1-flash-image-preview") ||
+    normalized.includes("nano-banana-2") ||
+    compact.includes("nanobanana2")
+  ) {
+    return "nano-banana-2";
+  }
+  if (
+    normalized.includes("gemini-3-pro-image-preview") ||
+    normalized.includes("nano-banana-pro") ||
+    compact.includes("nanobananapro")
+  ) {
+    return "nano-banana-pro";
+  }
+  if (normalized.includes("gpt-image-2") || compact.includes("gptimage2")) {
+    return "gpt-image-2";
+  }
+  return "";
+}
+
+function getCanvasScaleAdjustModelFamily(item: CanvasModelWithProvider) {
+  return (
+    resolveCanvasScaleAdjustModelFamilyFromText(item.model.modelId) ||
+    resolveCanvasScaleAdjustModelFamilyFromText(item.model.displayName) ||
+    resolveCanvasScaleAdjustModelFamilyFromText(item.model.id)
+  );
+}
+
 function tokenizeModelNameForSimilarity(value: unknown) {
   const normalized = normalizeModelNameForSimilarity(value);
   const compact = normalized.replace(/[^a-z0-9\u4e00-\u9fa5]+/g, "");
@@ -1795,10 +1828,17 @@ function findCanvasFailoverModel(params: {
   failedModelRefs: string[];
   preferLowCostSameNameProviders?: boolean;
   requiresImageInput?: boolean;
+  scaleAdjustModelFamily?: string | null;
 }) {
   const failedRefs = new Set(
     params.failedModelRefs.map((item) => String(item || "").trim()).filter(Boolean)
   );
+  const strictScaleAdjustModelFamily =
+    params.preferLowCostSameNameProviders &&
+    typeof params.scaleAdjustModelFamily === "string" &&
+    params.scaleAdjustModelFamily.trim()
+      ? params.scaleAdjustModelFamily.trim()
+      : "";
   const selectedFallbackRefs = [
     params.selectedModel.model.fallbackModelId1,
     params.selectedModel.model.fallbackModelId2,
@@ -1807,10 +1847,17 @@ function findCanvasFailoverModel(params: {
     .filter(Boolean);
 
   const isUsableFallback = (item: CanvasModelWithProvider) => {
+    const isSameFamilyScaleAdjustFallback = strictScaleAdjustModelFamily
+      ? getCanvasScaleAdjustModelFamily(item) === strictScaleAdjustModelFamily
+      : false;
     const isSameNameScaleAdjustFallback =
       params.preferLowCostSameNameProviders &&
-      scoreModelNameSimilarity(params.selectedModel, item) >=
+      (isSameFamilyScaleAdjustFallback ||
-        CANVAS_FAILOVER_SAME_NAME_THRESHOLD;
+        scoreModelNameSimilarity(params.selectedModel, item) >=
+          CANVAS_FAILOVER_SAME_NAME_THRESHOLD);
+    if (strictScaleAdjustModelFamily && !isSameFamilyScaleAdjustFallback) {
+      return false;
+    }
     if (
       !item.model.isEnabled ||
       item.model.isSubModel ||
@@ -1849,6 +1896,18 @@ function findCanvasFailoverModel(params: {
       sameProviderType: item.provider.type === params.selectedModel.provider.type,
     }))
     .sort((left, right) => {
+      if (strictScaleAdjustModelFamily) {
+        const leftPriority = getCanvasScaleAdjustFailoverPriority(left.item);
+        const rightPriority = getCanvasScaleAdjustFailoverPriority(right.item);
+        if (leftPriority !== rightPriority) return leftPriority - rightPriority;
+        if (right.nameSimilarity !== left.nameSimilarity) {
+          return right.nameSimilarity - left.nameSimilarity;
+        }
+        if (left.sameProviderType !== right.sameProviderType) {
+          return left.sameProviderType ? -1 : 1;
+        }
+        return left.index - right.index;
+      }
       const leftSameName =
         left.nameSimilarity >= CANVAS_FAILOVER_SAME_NAME_THRESHOLD;
       const rightSameName =
@@ -1922,6 +1981,10 @@ export async function generateCanvasImage(
     request.debugMeta && typeof request.debugMeta === "object"
       ? request.debugMeta
       : undefined;
+  const scaleAdjustModelFamily =
+    typeof debugMeta?.scaleAdjustModelFamily === "string"
+      ? debugMeta.scaleAdjustModelFamily.trim()
+      : "";
   const localEditComposite = normalizeLocalEditCompositeConfig(
     request.localEditComposite
   );
@@ -1974,6 +2037,7 @@ export async function generateCanvasImage(
         debugMeta?.scaleAdjustPreferSameNameProviderFailover
       ),
       requiresImageInput,
+      scaleAdjustModelFamily,
     });
 
     if (!imageInputFallback) {
@@ -2578,6 +2642,7 @@ export async function generateCanvasImage(
           debugMeta?.scaleAdjustPreferSameNameProviderFailover
         ),
         requiresImageInput: normalizedReferenceImages.length > 0,
+        scaleAdjustModelFamily,
       })
     : null;