修复布尔范围操作重复执行

- 重新开始区域合并或重叠区域去除时取消旧的顶栏按帧范围请求
- 防止先选择按帧范围、再处理当前帧后还能继续执行旧范围合并
- 补充 VideoWorkspace 回归测试覆盖旧范围请求被取消的路径
- 更新项目指南、设计冻结和测试计划中的互斥交互说明

src/components/VideoWorkspace.tsx

@@ -1015,6 +1015,17 @@ export function VideoWorkspace({ onNavigateToAI }: { onNavigateToAI?: () => void
     setStatusMessage(`请选择${booleanOperationLabel(request.operation)}帧范围，再点击“确认${booleanOperationLabel(request.operation)}”`);
   }, [frameNumberById]);
 
+  const clearPendingBooleanRangeSelection = useCallback(() => {
+    setPendingBooleanRangeRequest(null);
+    setPendingBooleanRangeConfirm(null);
+    if (rangeSelectionMode === 'boolean') {
+      setRangeSelectionMode(null);
+      setIsPropagationRangeSelecting(false);
+      setHasExplicitPropagationRange(false);
+      setStatusMessage('');
+    }
+  }, [rangeSelectionMode]);
+
   const handleConfirmBooleanFrameRangeOperation = useCallback(() => {
     if (!pendingBooleanRangeRequest || frames.length === 0) return;
     const clampRangeFrameNumber = (value: number) => {
@@ -2114,6 +2125,7 @@ export function VideoWorkspace({ onNavigateToAI }: { onNavigateToAI?: () => void
               totalFrames={totalFrames}
               onRequestDeleteMasks={(maskIds) => void handleDeleteSelectedMasks(maskIds)}
               onRequestBooleanFrameRange={handleBooleanFrameRangeRequest}
+              onBooleanOperationStart={clearPendingBooleanRangeSelection}
               onDeleteMaskAnnotations={handleDeleteMaskAnnotations}
             />
           </div>