PgIndexer
Writes a source PostgresDriver.Transaction into XT via the supplied OpenTx.
The source owns the token, system-time and failure model — the indexer runs inside a token-managed OpenTx and just decides what to write. Snapshot and streaming both arrive as a PostgresDriver.Transaction; the snapshot path synthesises one per batch so there is a single entry point.
Each op carries its source schema/table (RowOp), so an indexer can re-route tables, derive _id, drop or mask columns, or filter ops entirely. The reference DirectMirror mirrors the upstream as-is and has no privileged access — it uses the same OpenTx surface as any indexer.