fix(#3659): make the worktree base-check trust evidence, not baseRef (#3736)
* test(#3659): baseref-head suppress must be mode-aware regression rows
* fix(#3659): make baseref-head suppress mode-aware and thread isolation mode
* fix(#3659): review fixes - stale advice purge, message pins, mode alias
* fix(#3659): pick-interceptable emit seam, ack merge, writeSync pin
* test(#3659): rewrite set-baseref pin, fix writeSync row stub
* chore(#3659): backfill changeset pr number
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Co-authored-by: sim <sim@local>