> very few if any posts have 65..100 tags In fact, one can systematize based upon that to keep the hot-path memory footprint small by using 1 bit out of the 64 as an "overflow flag". So, e.g. up to 63 tags work with the bit-vector and the ones past that (64..100) are treated specially as done, for example, in <https://github.com/c-blake/ndup/blob/main/ndup/invidx.nim> with four 16-bit file numbers can be packed into one 64-bit number.
I haven't read about this, but it sure sounds like one of those "open ended interview questions" where these kinds of optimization ideas are elaborated upon after the candidate gets some initial, slow impl working.
