The hot per-artifact queries in the phantom-fill crosslink cascade — the content/blob-by-rid lookup and the per-node orphan/delta-child lookups in afterDephantomize — re-tokenized, re-parsed, and re-compiled their SQL text on every call because db.Querier delegated straight to the raw driver each time with no statement reuse. On a large repository (67k+ artifacts) the SQLite parser/compiler dominated CPU during the slow clone stretch.

Add a statement cache to both Querier implementations, keyed by exact query text, with lifetimes matched to each backing type:

- *DB caches *sql.Stmt prepared from its long-lived *sql.DB pool (safe for concurrent use, manages its own connections). Statements are prepared lazily on first use, reused thereafter, and closed in DB.Close. - *Tx caches *sql.Stmt scoped to a single *sql.Tx; the cache is torn down (all statements closed) when the transaction commits or rolls back, so no statement outlives its transaction or leaks across a clone/sync session.

Exec/QueryRow/Query transparently get-or-prepare the cached statement — no signature or caller-visible behavior change. QueryRow preserves database/sql's deferred-error contract by falling back to the raw path on prepare failure so the error still surfaces from Scan. Multi-statement strings (DDL setup batches) bypass the cache and run through the raw driver path, since a prepared statement compiles only one statement.

Benchmark (Apple M4 Pro, modernc driver): the blob-by-rid lookup drops from 4779 ns/op to 2289 ns/op (~2.1x). Cache reuse, transaction-boundary cleanup, and multi-statement bypass are covered by new tests in db/stmtcache_test.go. check-in: 218ebaec74 user: [email protected] tags: trunk