diff --git a/lib/canvas/generate-image.ts b/lib/canvas/generate-image.ts
index 3c7dfa44f..2ae709c20 100644
--- a/lib/canvas/generate-image.ts
+++ b/lib/canvas/generate-image.ts
@@ -4917,7 +4917,7 @@ export async function generateCanvasImage(
     : imageModels.find((m) => m.model.isDefault) || imageModels[0];
 
   if (!selectedModel) {
-    if (model && request.allowFailover === false) throw new Error("指定的图片模型不可用，未切换到其他模型");
+    if (model && (model !== "auto" || request.agentImageMode === "pinned") && request.allowFailover === false) throw new Error("指定的图片模型不可用，未切换到其他模型");
     selectedModel = request.agentImageMode === "auto" ? imageModels.find(entry => !entry.model.excludeFromFailover) : imageModels[0];
     if (!selectedModel) throw new Error("当前没有可用的备用图片模型，请稍后重试");
   }
diff --git a/tests/routes/canvas-agent-runtime-image-failover.test.ts b/tests/routes/canvas-agent-runtime-image-failover.test.ts
index b53ac7683..19ec552a0 100644
--- a/tests/routes/canvas-agent-runtime-image-failover.test.ts
+++ b/tests/routes/canvas-agent-runtime-image-failover.test.ts
@@ -61,3 +61,10 @@ test("automatic fallback respects requested dimensions, disabled candidates and
   const result = await h.generate({ ...h.request, agentImageMaxCreditCost: 3 });
   expect(result.modelRef).toBe("backup"); expect(h.calls.map(c => c.id)).toEqual(["primary", "backup"]);
 });
+
+
+test("the existing non-Agent auto alias continues to select its configured default", async () => {
+  const h = harness();
+  const result = await h.generate({ ...h.request, model: "auto", agentImageMode: undefined, allowFailover: false });
+  expect(result.modelRef).toBe("primary"); expect(h.calls).toHaveLength(1);
+});