Function carry_into 

pub fn carry_into(
    own: &Path,
    java: &[Held],
    region: Option<&Region>,
    now_ms: i64,
) -> Result<usize, String>

Java’s new calls copied into this phone’s own log (own), under its lock, read again there: those whose line is not in it yet (by its id), never a blocked caller’s, nor one past KEPT_DAYS (taken out already, it would come back). Two processes copying at once never write a line twice. Returns how many lines were written.