Dedup DELETE + note clamp before the DDL so the unique index and CHECK
cannot fail mid-migration (failed Flyway row -> backend boot loop) on a
DB that served writes under the old code (no dedup guard, 5000-char
notes). No-ops on a clean database.
Note: this changes V74's checksum — dev databases that already ran V74
on this branch need 'flyway repair' (or a fresh DB). CI and prod run
from V73 or clean and are unaffected.
Review round 3: Tobias (1).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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