Key under which an Error carries its HttpStatusHint.

Created with Symbol.for, not Symbol(), so two copies of this package in one process resolve the same key — the failure mode a locally-constructed symbol would produce silently, since every read would simply miss. This is the SECURITY_METADATA precedent (M57).

Prefer withHttpStatusHint and httpStatusHintOf over touching this directly; the symbol is exported so an error thrown outside this repository can be branded too.