The guard was argued empirically ("none of the 91 shims on this box has one"),
which invites a future reader to relax it for a shim we have not seen. Windows
reserves `:` within a path segment, so a relative path cannot carry one at all:
the only spellings that can are drive-qualified, an alternate data stream, or a
`\?\` device path, and the last is already refused as absolute. That makes a
false refusal impossible rather than unobserved.
Orca Worker
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