mine1 search analysis

Spec: probs/problem-mine1.lisp (tree, first solution, depth cutoff 16, a wait
action asserting (waiting), happenings).

Parallel wait fix (2026-10-15): the wait action no longer writes the static
database, so mine1 runs with threads.  First solution, 16 steps, serial and
16 threads.  Details in doc/problems/sentry/search-analysis.txt.

Current-path check with happenings (2026-10-15): the check now also compares
each happening's place in its cycle and the wait flag.  First solution at
cutoff 16, program cycles (Linux SBCL 2.6.9):
  before the change, serial            16,667
  before the change, 16 threads        67,213
  after, serial                       605,169
  after, 16 threads                   387,468
  after, without the wait flag        386,932 (serial)
  after, failed-state memory on         3,000 (serial; recorded 824 states,
                                        skipped 1,115 nodes)
All runs: one 16-step solution.  Failed-state memory replaces the check and
is the setting to use for this problem.

Forms:
  (stage mine1)
  (ww-set *failed-state-memory* t)
  (solve)
