12 tests drive the real seqjob plugin through job_alloc_fn and record
today's results, reasons and debits, with switch-stable OOM injection
(sched_make_allocs stub, --wrap of make_host_alloc/make_job_alloc).
Assertions the runner changes on purpose sit in *_today tests.
The characterization showed bug-1893's real effect: vget() returns 0 on
success, so the shared-reason loop (rc <= 0 skip) never records a shared
NO_RESOURCE reason. Bug record and spec wording corrected; the runner
skips only on rc < 0.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>