The last of the DAG-container removal. `tests.rs` navigated by the id
`submit` returned, so removing the container removed the tests' way of
finding what they inserted; they name the roots they assert on now, which
is the same handle production uses.
Three findings the port surfaced, each a behaviour change rather than a
test fix:
- Cancelling a rebuild's head no longer drops the job. `Reconcile`'s edge
accepts a skipped brace, and a cancel-cascade skips rather than cancels,
so the tail stays claimable. Dropping a job means cancelling every id the
insert returned.
- A directly-cancelled group root reads terminal while a spared tail still
runs; the cancel used to land on a node above it, which rolled up
Finishing instead.
- "One DAG per hive-wide op" is not expressible without a container. The
three tests asserting it now assert that every named root is top-level,
which is what makes the per-agent subgraphs concurrent.
Deletes two tests: one asserted only that two containers get distinct ids,
the other re-ran an existing case under a second name.
`Source`, `insert_group` and the stop path's `reason` string went dead with
the container and are removed with it.
ddc017f01b