fix(desktop): error response improvements — content, retry, model selector

P1: onError callback now sets content to error message instead of empty string.
    Previously API errors (404/429) produced empty assistant messages with only
    a visual error badge — now the error text is persisted in message content.

P3: Retry button now re-sends the preceding user message via sendToGateway
    instead of copying to input. Works for both virtualized and non-virtualized
    message lists. Removed unused setInput prop from MessageBubble.

Also hides model selector in Tauri runtime (SaaS token pool routes models).

desktop/src/components/ChatArea.tsx

@@ -231,6 +231,18 @@ export function ChatArea({ compact, onOpenDetail }: { compact?: boolean; onOpenD
     setPendingFiles([]);
   };
 
+  const createRetryHandler = (msgId: string) => () => {
+    if (isStreaming) return;
+    // Find the user message immediately before this error
+    const idx = messages.findIndex(m => m.id === msgId);
+    if (idx > 0) {
+      const prevMsg = messages[idx - 1];
+      if (prevMsg.role === 'user' && prevMsg.content) {
+        sendToGateway(prevMsg.content);
+      }
+    }
+  };
+
   const handleKeyDown = (e: React.KeyboardEvent) => {
     if (e.key === 'Enter' && !e.shiftKey) {
       e.preventDefault();
@@ -433,6 +445,16 @@ export function ChatArea({ compact, onOpenDetail }: { compact?: boolean; onOpenD
               onHeightChange={setHeight}
               messageRefs={messageRefs}
               setInput={setInput}
+              retryForMessage={(msgId: string) => {
+                const idx = messages.findIndex(m => m.id === msgId);
+                if (idx > 0) {
+                  const prevMsg = messages[idx - 1];
+                  if (prevMsg.role === 'user' && prevMsg.content) {
+                    return () => { if (!isStreaming) sendToGateway(prevMsg.content); };
+                  }
+                }
+                return undefined;
+              }}
             />
           ) : (
             messages.map((message) => (
@@ -445,7 +467,7 @@ export function ChatArea({ compact, onOpenDetail }: { compact?: boolean; onOpenD
                 layout
                 transition={defaultTransition}
               >
-                <MessageBubble message={message} setInput={setInput} />
+                <MessageBubble message={message} onRetry={createRetryHandler(message.id)} />
               </motion.div>
             ))
           )}
@@ -575,7 +597,7 @@ export function ChatArea({ compact, onOpenDetail }: { compact?: boolean; onOpenD
   );
 }
 
-function MessageBubble({ message, setInput, onRetry }: { message: Message; setInput: (text: string) => void; onRetry?: () => void }) {
+function MessageBubble({ message, onRetry }: { message: Message; setInput?: (text: string) => void; onRetry?: () => void }) {
   if (message.role === 'tool') {
     return null;
   }
@@ -679,17 +701,14 @@ function MessageBubble({ message, setInput, onRetry }: { message: Message; setIn
             {message.error && (
               <div className="flex items-center gap-2 mt-2">
                 <p className="text-xs text-red-500">{message.error}</p>
-                <button
-                  onClick={() => {
-                    const text = typeof message.content === 'string' ? message.content : '';
-                    if (text) {
-                      setInput(text);
-                    }
-                  }}
-                  className="text-xs px-2 py-0.5 rounded bg-red-100 dark:bg-red-900/30 text-red-600 dark:text-red-400 hover:bg-red-200 dark:hover:bg-red-900/50 transition-colors"
-                >
-                  重试
-                </button>
+                {onRetry && (
+                  <button
+                    onClick={onRetry}
+                    className="text-xs px-2 py-0.5 rounded bg-red-100 dark:bg-red-900/30 text-red-600 dark:text-red-400 hover:bg-red-200 dark:hover:bg-red-900/50 transition-colors"
+                  >
+                    重试
+                  </button>
+                )}
               </div>
             )}
             {/* Download button for AI messages - show on hover */}
@@ -716,6 +735,7 @@ interface VirtualizedMessageRowProps {
   onHeightChange: (height: number) => void;
   messageRefs: MutableRefObject<Map<string, HTMLDivElement>>;
   setInput: (text: string) => void;
+  onRetry?: () => void;
 }
 
 /**
@@ -726,7 +746,7 @@ function VirtualizedMessageRow({
   message,
   onHeightChange,
   messageRefs,
-  setInput,
+  onRetry,
   style,
   ariaAttributes,
 }: VirtualizedMessageRowProps & {
@@ -761,7 +781,7 @@ function VirtualizedMessageRow({
       className="py-3"
       {...ariaAttributes}
     >
-      <MessageBubble message={message} setInput={setInput} />
+      <MessageBubble message={message} onRetry={onRetry} />
     </div>
   );
 }
@@ -773,6 +793,7 @@ interface VirtualizedMessageListProps {
   onHeightChange: (id: string, height: number) => void;
   messageRefs: MutableRefObject<Map<string, HTMLDivElement>>;
   setInput: (text: string) => void;
+  retryForMessage: (msgId: string) => (() => void) | undefined;
 }
 
 /**
@@ -786,6 +807,7 @@ function VirtualizedMessageList({
   onHeightChange,
   messageRefs,
   setInput,
+  retryForMessage,
 }: VirtualizedMessageListProps) {
   // Row component for react-window v2
   const RowComponent = (props: {
@@ -802,6 +824,7 @@ function VirtualizedMessageList({
       onHeightChange={(h) => onHeightChange(messages[props.index].id, h)}
       messageRefs={messageRefs}
       setInput={setInput}
+      onRetry={retryForMessage(messages[props.index].id)}
       style={props.style}
       ariaAttributes={props.ariaAttributes}
     />

desktop/src/store/chat/streamStore.ts

@@ -502,10 +502,17 @@ export const useStreamStore = create<StreamState>()(
             }
           },
           onError: (error: string) => {
+            // Flush any remaining buffered deltas before erroring
+            if (flushTimer !== null) {
+              clearTimeout(flushTimer);
+              flushTimer = null;
+            }
+            flushBuffers();
+
             _chat?.updateMessages(msgs =>
               msgs.map(m =>
                 m.id === assistantId
-                  ? { ...m, content: '', streaming: false, error }
+                  ? { ...m, content: error, streaming: false, error }
                   : m.role === 'user' && m.optimistic && m.timestamp.getTime() >= streamStartTime
                     ? { ...m, optimistic: false }
                     : m