fix: single gpt-5.4 model selector + SSE buffer edge case fix

- Replace Flash/Pro dual model buttons with single "gpt-5.4" label
- Backend still receives "flash" as model param (matches schema validation)
- Remove unused selectedModel/onSelectedModelChange props from GeminiInput
- Fix SSE stream parsing: process remaining buffer data when stream ends
  without trailing newline (potential cause of "no return" issue)

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

frontend/components/gemini/GeminiChat.tsx

@@ -72,7 +72,7 @@ export function GeminiChat() {
   const [extensions, setExtensions] = useState<Extension[]>(INITIAL_EXTENSIONS);
   const [ticketSummary, setTicketSummary] = useState<TicketSummaryData | null>(null);
   const [activeTools, setActiveTools] = useState<Set<string>>(new Set());
-  const [selectedModel, setSelectedModel] = useState<"flash" | "pro">("pro");
+  const [selectedModel, setSelectedModel] = useState<"flash" | "pro">("flash");
   const messagesEndRef = useRef<HTMLDivElement>(null);
   const abortRef = useRef<AbortController | null>(null);
 
@@ -381,8 +381,6 @@ export function GeminiChat() {
           isLoading={isLoading}
           activeTools={activeTools}
           onActiveToolsChange={setActiveTools}
-          selectedModel={selectedModel}
-          onSelectedModelChange={setSelectedModel}
         />
       </div>
 

frontend/components/gemini/GeminiInput.tsx

@@ -27,8 +27,6 @@ interface GeminiInputProps {
   isLoading?: boolean;
   activeTools: Set<string>;
   onActiveToolsChange: (tools: Set<string>) => void;
-  selectedModel: "flash" | "pro";
-  onSelectedModelChange: (model: "flash" | "pro") => void;
 }
 
 const TOOLS: Tool[] = [
@@ -45,8 +43,6 @@ export function GeminiInput({
   isLoading,
   activeTools,
   onActiveToolsChange,
-  selectedModel,
-  onSelectedModelChange,
 }: GeminiInputProps) {
   const textareaRef = useRef<HTMLTextAreaElement>(null);
   const fileInputRef = useRef<HTMLInputElement>(null);
@@ -204,32 +200,13 @@ export function GeminiInput({
             </div>
           </div>
 
-          {/* Bottom row: Model selector */}
+          {/* Bottom row: Model indicator */}
           <div className="flex items-center justify-end px-4 pb-3 pt-0 gap-2">
-            <button
-              onClick={() => onSelectedModelChange("flash")}
-              className={cn(
-                "px-3 py-1.5 rounded-full text-xs font-medium transition-all duration-150 cursor-pointer",
-                selectedModel === "flash"
-                  ? "bg-[var(--gem-blue)] text-white"
-                  : "bg-[var(--gem-surface-2)] text-[var(--gem-text-muted)] hover:bg-[var(--gem-surface-3)] hover:text-[var(--gem-text)]"
-              )}
-              aria-pressed={selectedModel === "flash"}
+            <span
+              className="px-3 py-1.5 rounded-full text-xs font-medium bg-[var(--gem-blue)] text-white"
             >
-              Flash
-            </button>
-            <button
-              onClick={() => onSelectedModelChange("pro")}
-              className={cn(
-                "px-3 py-1.5 rounded-full text-xs font-medium transition-all duration-150 cursor-pointer",
-                selectedModel === "pro"
-                  ? "bg-[var(--gem-purple)] text-white"
-                  : "bg-[var(--gem-surface-2)] text-[var(--gem-text-muted)] hover:bg-[var(--gem-surface-3)] hover:text-[var(--gem-text)]"
-              )}
-              aria-pressed={selectedModel === "pro"}
-            >
-              Pro
-            </button>
+              gpt-5.4
+            </span>
           </div>
 
           {/* Tools panel (collapsible, below input) */}

frontend/lib/api.ts

@@ -114,7 +114,24 @@ export function streamChat(
 
       while (true) {
         const { done, value } = await reader.read();
-        if (done) break;
+        if (done) {
+          // Process any remaining data in buffer (last line may lack trailing newline)
+          if (buffer.trim()) {
+            const trimmed = buffer.trim();
+            if (trimmed.startsWith("data: ")) {
+              const json = trimmed.slice(6);
+              if (json) {
+                try {
+                  const event: ChatStreamEvent = JSON.parse(json);
+                  onEvent(event);
+                } catch {
+                  // skip malformed
+                }
+              }
+            }
+          }
+          break;
+        }
 
         buffer += decoder.decode(value, { stream: true });
         const lines = buffer.split("\n");