during/spawn used not to add linkage assertions to its
initial-assertion set. In addition, if a spawned actor died in its
initial boot procedure, its initial assertions would never be visible.
These two problems interlocked to cause a space leak in during/spawn,
where monitoring facets would never be cleaned up.
This change does two things:
- adds linkage assertions to the initial-assertion set in during/spawn
- properly briefly signals initial-assertions even when a new actor
immediately crashes.
Together, these repair the space leak in during/spawn with a crashy
child startup procedure.