> "Turns out, this is part of macOS 27.0…"

Part of macOS 26.4, in fact: https://eclecticlight.co/2026/09/19/macos-tahoe-26-4-changed... "The layout of those hasn’t changed in over six years up to and including macOS Tahoe 26.3.1, but has altered in 26.4 and Golden Gate, with the addition of a new firmlinked directory pkg."

Apple doesn't do this stuff lightly. A search of WWDC sessions doesn't mention /pkg specifically, but I'd bet it's related to this: https://developer.apple.com/videos/play/wwdc2026/206/?time=6...