error_is_truncated submitted a DAG, claimed its head, failed it with a
long string and read the error back out of a snapshot -- four moving
parts to observe one `&str -> String`. The DAG round-trip it depended on
is covered by its own tests either way.
Testing truncate_error directly also reaches the case the round-trip
never could: the cap is a byte length, so a multibyte char straddling it
would panic the slice. That boundary scan is the only non-obvious line
in the function and it had no coverage at all -- the old test used a
repeated ASCII 'x', where byte and char offsets coincide.
Also drops a stale claim from insert_job's doc: it has not recorded a
per-node node_rt since that map was deleted.
a59ad5ce3f