refactor(webui): infer fallback from active model

webui/src/components/thread/ThreadShell.tsx

@@ -400,7 +400,7 @@ function toModelBadgeInfo(
   );
   return {
     label,
-    model: toModelBadgeLabel(model),
+    model: model?.trim() || null,
     provider,
     providerLabel: provider ? providerDisplayLabel(settings?.providers ?? [], provider) : null,
     needsSetup,
@@ -959,9 +959,12 @@ export function ThreadShell({
     setFallbackModelName(null);
     return client.onChat(chatId, (event) => {
       if (event.event !== "turn_model_updated") return;
-      setFallbackModelName(event.is_fallback ? event.model_name : null);
+      const activeModel = event.model_name.trim();
+      setFallbackModelName(
+        modelBadge.model && activeModel !== modelBadge.model ? activeModel : null,
+      );
     });
-  }, [chatId, client]);
+  }, [chatId, client, modelBadge.model]);
 
   useEffect(() => {
     if (!historyKey || !chatId || loading) return;
@@ -1451,7 +1454,7 @@ export function ThreadShell({
               : t("thread.composer.placeholderThread")
           }
           modelLabel={modelBadgeLabel}
-          modelDetail={modelBadge.model}
+          modelDetail={toModelBadgeLabel(modelBadge.model)}
           modelPreset={activeModelPreset}
           modelPresets={modelPresetOptions}
           onModelPresetChange={handleModelPresetChange}
@@ -1498,7 +1501,7 @@ export function ThreadShell({
               : t("thread.composer.placeholderHero")
           }
           modelLabel={modelBadgeLabel}
-          modelDetail={modelBadge.model}
+          modelDetail={toModelBadgeLabel(modelBadge.model)}
           modelPreset={activeModelPreset}
           modelPresets={modelPresetOptions}
           onModelPresetChange={handleModelPresetChange}

webui/src/lib/types.ts

@@ -1313,7 +1313,6 @@ export type InboundEvent =
       chat_id: string;
       model_name: string;
       model_preset?: string | null;
-      is_fallback?: boolean;
     }
   | ({
       event: "turn_end";

webui/src/tests/nanobot-client.test.ts

@@ -1724,7 +1724,6 @@ describe("NanobotClient", () => {
       chat_id: "chat-a",
       model_name: "deepseek/deepseek-chat",
       model_preset: "Deep Research",
-      is_fallback: true,
     });
 
     expect(chatHandler).toHaveBeenCalledWith({
@@ -1732,7 +1731,6 @@ describe("NanobotClient", () => {
       chat_id: "chat-a",
       model_name: "deepseek/deepseek-chat",
       model_preset: "Deep Research",
-      is_fallback: true,
     });
   });
 

webui/src/tests/thread-shell.test.tsx

@@ -720,7 +720,6 @@ describe("ThreadShell", () => {
         event: "turn_model_updated",
         chat_id: "fallback-model",
         model_name: "openai-codex/gpt-5.5",
-        is_fallback: false,
       });
     });
 
@@ -731,7 +730,6 @@ describe("ThreadShell", () => {
         event: "turn_model_updated",
         chat_id: "fallback-model",
         model_name: "deepseek/deepseek-chat",
-        is_fallback: true,
       });
     });