crossrealm_d state

counter

init.1

SetCounter

SetCounter: non-crossing. Calling this cross-realm triggers the readonly check because it directly assigns a package var.

SetCounterCrossing

SetCounterCrossing: crossing version. This works correctly cross-realm because the caller enters this realm's context.

GetCounter

DoubleCounter

DoubleCounter reads counter and doubles it. Used to show that if counter were silently corrupted in memory, subsequent crossing calls would act on the wrong value.

MutateBytes

MutateBytes mutates the first byte of bz to 0xff. Used to test whether a foreign realm can write to caller-allocated bytes. Under storage=authority, bz has PkgID=caller; borrow rule #1 here makes m.Realm=crossrealm\_d (declaring realm); the write site (bz\[0] = ...) should fire readonly because bz.PkgID != m.Realm.ID.