Handing an Artifact subscription to another session now reads as "yielded" instead of looking like a failure.
What's wrong with this entry?
When a live Artifact subscription is handed to another session, its stopped watch is now reported as "yielded" rather than "interrupt", "swept" or "killed", so a deliberate hand-off no longer reads as a failure.
- The hand-off path also emits counters for each way it can go wrong: malformed frame, unvettable target, unverified requester, table full, handler threw, stale request, ambiguous answer send, undelivered answer, and two pid-mismatch cases, plus a count of successful hand-backs.
yield_handed_back
Strings lifted out of the shipped bundle, so the claim above can be checked against them.