`Error.location` is a `^T`

Decided

D-0030, settled by the language’s author: part of spec §18. Older text cites it as 18.30.

It is a &SourceLocation, the one reference the language stores in a struct: the location lives in static storage for the whole program, so the reason §18.3 bans stored references does not apply. e.location.line reads it directly, and Error stays 32 bytes. User structs still cannot store a reference (§9.2)