Function ensure_unique_pk_index 

pub fn ensure_unique_pk_index(
    conn: &Connection,
    table: &str,
    ts: &TableSchema,
) -> Result<(), ReplicaError>

Ensure the table has a UNIQUE index covering exactly the PK columns, which TableSource requires for row-identity point lookups. Idempotent.

A rowid-alias INTEGER PRIMARY KEY is skipped: the rowid already enforces uniqueness and SQLite point-looks-it-up natively (SEARCH … USING INTEGER PRIMARY KEY (rowid=?)), so a synthetic index would be pure write amplification with no plan benefit — and TableSource recognizes the rowid alias as a unique key without one. (Databases created by older versions may still carry a now-unused rindle_replica_pk_* index; it is harmless and left in place.)

One implementation, shared with the apply plane (crate::apply::ensure_unique_pk_index_for, design 309) — this is the ColumnDef-shaped adapter for hosts on the embedded-engine seam.