Function is_sqlite_busy 

pub fn is_sqlite_busy(err: &AppError) -> bool

Returns true when err wraps an SQLITE_BUSY (or SQLITE_LOCKED) condition reported by rusqlite.

Both SQLITE_BUSY (ErrorCode::DatabaseBusy) and SQLITE_LOCKED (ErrorCode::DatabaseLocked) indicate that the write cannot proceed immediately due to WAL concurrency. We treat both as transient and eligible for retry.