OMFG, it's happening because I made builds faster. This nightmare to debug (because it happens in a remote secure container) is evidently a combination of:
1. A unit test result folder that slipped into the file set
2. A test output folder being time-based but only down to the millisecond, so think: <Prefix>_12_01_02.123\
3. When there's a collision (e.g. 2 at the same millisecond), there's an indexer, making it <Prefix>_12_01_02.123[2]\
4. The PowerShell script wrapping some other functionality in a package wasn't using -LiteralPath with user-input file paths, which means it thinks that `[2]` is a Regex.
My brain hurts.
@Nick_Craver this is hilarious, relatable, depressing, predictable, and arguably better than parsing html with regex.
Thanks for the smiles.