fix(pm): serve a verify-lock queue whose holds outlast one foreground turn (#12788)

The wait budget cannot be raised: it is spent inside one foreground agent
turn, which the harness kills at ~600s, so a larger number buys an
unreportable SIGTERM rather than a longer wait. What spans several turns is
the slot, and two things stopped it working:

- its ageing bound ran from the ORIGINAL arrival, so a caller queued behind
  two ~19-minute holds lost its place for the offence of the queue being
  long. The age now runs from when the place was last put down, which is the
  question the bound was always asking.
- it was named only in the exit-99 message, one whole budget after the place
  it would have kept was lost. A queueing caller is now told at second zero.

Exclusion, FIFO order, the cap and the budget are unchanged.


Claude-Session: https://claude.ai/code/session_01PfaSTikked61BkcsB5Rn69

Co-authored-by: Claude <noreply@anthropic.com>

Author: claude[bot]