seedCycle ignored upsertDecisions and unconditionally INSERTed, so a
re-run against a non-empty sandbox failed every row in a cycle SCC
with DUPLICATE_VALUE on its external-id. Now routes picked ext-id
rows through composite UPSERT (matching seedSingle), and omits the
break-field on UPSERT bodies so matched existing rows keep their
live FK.

Regression: tests/seed/cycle-upsert.test.ts.