Function begin_immediate 

pub async fn begin_immediate(
    pool: &SqlitePool,
) -> Result<Transaction<'static, Sqlite>>

Begin a WRITE transaction with BEGIN IMMEDIATE.

sqlx’s pool.begin() issues a deferred BEGIN: a transaction that reads before it writes pins its read snapshot on the first statement, and if another connection commits in between, the later write cannot upgrade — SQLite returns a busy-snapshot error even with a busy_timeout, because the conflict is logical, not a lock wait. BEGIN IMMEDIATE takes the write lock up front, so a read-then-write transaction is safe under WAL’s single-writer rule.