fix(agent): hide unrelated models for alias fallback

src/lib/llm/models.ts

@@ -75,14 +75,19 @@ export async function listLlmModels(options?: {
     }
 
     const models = normalizeLlmModelsPayload(await response.json());
-    const merged = new Map<string, LlmModelOption>();
-    merged.set(fallbackModel, fallbackOption);
-    for (const model of models) merged.set(model.id, model);
+
+    if (models.length === 0) {
+      return { models: [fallbackOption], fallbackModel, degraded: true };
+    }
+
+    if (!models.some((model) => model.id === fallbackModel)) {
+      return { models: [fallbackOption], fallbackModel, degraded: false };
+    }
 
     return {
-      models: [...merged.values()].sort((a, b) => a.id.localeCompare(b.id)),
+      models,
       fallbackModel,
-      degraded: models.length === 0,
+      degraded: false,
     };
   } catch {
     return { models: [fallbackOption], fallbackModel, degraded: true };