Thanks a lot, that's awesome! I did think about the possible confusion with modern passkeys, but eventually decided that shedding contamination with 21st century knowledge is fair as part of the puzzle.
Apparently “passkey” appears in exactly two movie titles (according to IMDB): The Devil’s Passkey (1920) and Passkey to Danger (1946). So it was probably more frequently used in 1934 than now. The poster for the latter implies that a passkey is an enormous six-foot long key. (jk)
Citations are thin, but the original definition (a skeleton key, opens multiple locks) seems at odds with WebAuthn (an individual user’s key for a single website).
Why the heck did “skeleton key” stick around and “passkey” fall into disuse? Sure, it sounds way cooler, but I would assume people who carry skeleton keys would prefer boring, professional terms for things.
It’s good to know you considered it. At the time it didn’t feel fair. But I guess that’s just how it goes with puzzles. There’s not much point to this comment other than maybe it will help someone else avoid the spoilers on the hints page.