1.39.1-prusa3d
macOS 10.13.4 (17E199)
Skirt / Brim generation is not respecting table operating size
If object is placed very near to table edge, brim and/or skrit is generated outside table, hence gcode also instructs printer to print outside operational dimensions.
I have the same issue with version 1.39.2 on Windows (10).
I also noticed that the support material extends beyond the edges of the bed also.
You are completely right, there is currently no check for the supports or brim/skirt against the working space.
We have a check in the current Slic3r-1.41.0-alpha3 in the G-code preview window. Does it satisfy your needs?
All it does is put up a warning telling you that it is off the print bed? You can already see that just by looking at the preview!

It needs to actually stop the brim (and supports) being generated or only create it(them) on the bed.
Most helpful comment
All it does is put up a warning telling you that it is off the print bed? You can already see that just by looking at the preview!
It needs to actually stop the brim (and supports) being generated or only create it(them) on the bed.