UPDATE: I found the file tucked inside a folder in ./Trash/Trash 00-48-20-799!
So Amber’s first hypothesis was correct, and I never thought to look, not in the Trash, but in a subfolder within the Trash.
Many of you probably recognize this “./Trash/Trash HH-MM-SS-µS” format … it’s DevonThink!
Yes, I had indexed (not imported) a scriv file to DevonThink and DT moved the original external file to the Trash even though I specified “Only In Database” option during trashing. That’s a mite concerning, but not as bad as all the paranoid explanatory metaphysics I came up with in the midst of the crisis.
Well, I used to enjoy some convenience from having scriv files indexed inside DT. But no more! Too much trauma. Lesson learned.
Thanks to the smart, caring people in this thread, and especially Amber for her astonishingly thorough replies that considered all the options. They ought to be in a help museum somewhere.