DEFERRED_INDEX_SQL unconditionally DROPs and re-CREATEs the four display
triggers on every open so a changed trigger body rolls out; DROP TRIGGER IF
EXISTS on an existing trigger takes the write lock, so a settled database
still blocked behind a sibling's transaction after the three statement
gates. Compare each trigger's stored sql against the desired CREATE text and
run the pair only when they differ. CREATE ... IF NOT EXISTS forms are
lock-free on an existing object and run as written. The no-writes test now
also traces DROP TRIGGER / ALTER.
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