Noir::LocatorKey(T)

A declared slot in CodeLocator.

T is the stored shape: String for single-value slots (set/get), Array(String) for append-only ones (push/all). CodeLocator takes LocatorKey(T) and never a bare String, so the compiler is the registry check — a literal key nobody declared does not build, and pushing to a single-value slot (or getting an append-only one) is a type error rather than a silently-empty read.

Before this, the locator was a blackboard of 63 magic strings: a detector wrote one, an analyzer read it, and nothing connected the two. The only way to learn that grpc-proto has two independent reader families was to grep for the string.