Very limited shared promotion

[Kagamin]

On Friday, 21 June 2019 at 18:11:38 UTC, Meta wrote:
> @trusted is allowed to do whatever it wants internally, as long 
> as it provides a *safe* interface. I believe that's what Manu's 
> getting at in regards to his @safe/@trusted distinction in 
> regards to threading.

Concurrency is indeed safe with that interface, so there's no 
reason to assume that it doesn't happen, and implicit conversion 
from thread local to shared is illegal.