Persists this run's entire stdout/stderr transcript to BACKUP_DIR
(/volume1/SMB-docker/backup) — the same directory the pg_dumpall
backup lands in. Appends to an already-open CUTOVER_SESSION_LOG if
invoked as a child of cutover.sh (merging into that session's single
transcript); opens its own rollback-standalone-<TS>.log if run
standalone (including a manual run long after the fact, per this
script's own asymmetry warning). This is the single highest-value
place for a durable transcript in the whole suite, since rollback.sh
failing partway is the one scenario RUNBOOK.md flags as requiring
manual intervention. Also logs the transcript path in the grace-window
refusal message so it's not lost even in that failure mode.
Console/SSH output unchanged (tee mirrors to both).
See ADR-0001 note, Session Update 9.