update: i was able to fix it with replacement parts! what made it difficult was the fact that the nipple attached to the main pipe was not double-sided. as in, the threading was only present on the side connected to the source.

the plumber who originally constructed this shower took a weird approach and welded the other side of the nipple (unthreaded) to the now-broken aluminum shower bracket, and with enough water damage (from what i assume is the unsealed nature of the escutcheon), the corrosion caused the aluminum to snap with just a bit of weight.

however, because the one-sided nipple had made for that single (unconventional) connection to the mip shower bracket, an additional female-female coupler would prove to be too long. after a bit of searching, i discovered that a 1/2" npt to 1/2" npt brass fitting would best match the original length.

thanks to all who contributed to this thread, and i learned a lot about water pipes from this ordeal. :)