Constant MIGRATIONS_JOURNAL_TABLE 

pub const MIGRATIONS_JOURNAL_TABLE: &'static str;

The producer-side migration journal (MIGRATIONS-VIA-CHANGELOG-DESIGN.md §4): a master’s record of “have I already minted a ddl journal frame for this migration id.” It is the idempotency key for the migrate surface (a re-POST of a known tag is a no-op), NOT the ordered transport — that is the journal’s ddl frame. Host-local, NOT registered for capture, so it never ships downstream (Drizzle-compatible tag, §3.2).