Let's ensure that all rectangles strictly snap to the grid points:

I've updated the code to ensure rectangles strictly snap to the grid points. Here are the key changes:

1. In the Canvas2D component:

   • Modified the snapToGrid function to use Math.floor instead of Math.round, ensuring coordinates always snap to the nearest grid point that's less than or equal to the current position
   • Updated the handleMouseUp function to ensure rectangle width and height are always multiples of the grid size
   • Set a minimum size of one grid cell for rectangles

2. In the main page component:

   • Added a gridSize constant to match the one in Canvas2D
   • Updated the example rectangles to have dimensions that are exact multiples of the grid size
   • Enhanced the handleUpdateRectangle function to ensure all rectangle properties (x, y, width, height) are snapped to the grid

These changes ensure that:

1. All rectangles are positioned at exact grid points
2. All rectangle dimensions are exact multiples of the grid size
3. When drawing or moving rectangles, they will always align perfectly with the grid
4. The example rectangles are also properly aligned to the grid

Now the rectangles will only snap to whole squares on the grid, making the layout more precise and predictable.

Let's modify the code to allow rectangles to overlap by exactly one grid square:

I've modified the code to allow rectangles to overlap by exactly one grid square, but not more than that. Here are the key changes:

1. Added a new hasExcessiveOverlap function in both components that:

   • Calculates the exact amount of overlap between two rectangles in both X and Y dimensions
   • Returns true only if the overlap exceeds one grid cell in either dimension
   • Returns false if there's no overlap or if the overlap is within the allowed limit (one grid cell)

2. Updated the overlap checking logic in:

   • handleMouseUp in Canvas2D (when creating new rectangles)
   • handleKeyDown in Canvas2D (when moving rectangles with arrow keys)
   • handleAddRectangle in the main page component
   • handleUpdateRectangle in the main page component

Now you can:

1. Create rectangles that overlap by one grid square
2. Move rectangles so they overlap with others by one grid square
3. But you cannot create or move rectangles to overlap by more than one grid square

This gives you the flexibility to create adjacent or slightly overlapping foundation elements while still maintaining a reasonable layout.