fix: 流式思考行随到随显，消除底部隐形占位空白

apps/desktop/src/renderer/src/components/Thinking.tsx

@@ -18,6 +18,11 @@ export function Thinking({
   const [manualExpanded, setManualExpanded] = useState<boolean | null>(null)
   const expanded = manualExpanded ?? streaming
 
+  // 流式轨迹的行必须「随到随显」：fade-up 的 both+delay 会让新行在延迟期间
+  // 透明但占高，流式期间底部因此持续留出一大片空白。交错入场只保留给
+  // 非流式一次性渲染的静态轨迹（挂载时决定，之后不变更，避免整段重播动画）。
+  const streamedMountRef = useRef(streaming)
+
   const traceRef = useRef<HTMLDivElement>(null)
   const [lineHeight, setLineHeight] = useState(0)
   useLayoutEffect(() => {
@@ -98,9 +103,13 @@ export function Thinking({
             <div ref={traceRef} className="flex flex-col gap-1 py-1">
               {rows.map((row, i) => (
                 <div
-                  key={`${i}-${row.primary.slice(0, 12)}`}
+                  key={i}
                   className="flex min-h-7 w-full items-start gap-2 rounded-control px-1.5 py-0.5 text-left"
-                  style={{ animation: `fade-up 400ms ease ${Math.min(i, 8) * 120}ms both` }}
+                  style={{
+                    animation: streamedMountRef.current
+                      ? 'fade-up 250ms ease'
+                      : `fade-up 400ms ease ${Math.min(i, 8) * 120}ms both`
+                  }}
                 >
                   <span className="min-w-0 text-[12.5px] leading-relaxed break-words text-ink-2">{row.primary}</span>
                 </div>