Constant SQLITE_PRAGMAS 

pub const SQLITE_PRAGMAS: &str = "PRAGMA journal_mode = WAL; PRAGMA busy_timeout = 5000; PRAGMA foreign_keys = ON;";

SQLite PRAGMAs applied to every connection for concurrent-access safety.

• WAL mode prevents SQLITE_BUSY when multiple processes access the DB
• 5-second busy timeout retries on transient lock contention
• Foreign key enforcement is off by default in SQLite