The supervision was already right — a clean exit means the host stood aside and
the launcher runs what is on disk, failures are counted, and a rollback happens
at the limit. Two things made it dead code: nothing told the running host a
successor was waiting, and the rollback resolved its known-good version through
pacman, which no machine here uses and which two of three operating systems do
not have.
Keeping a version rather than a path was the clue. Versions live side by side in
directories named for them; the newest runs; the running one stands aside between
reconciles; a reconcile that completes records itself and retires what is older
than its predecessor; rollback starts that predecessor. No new resource kind and
nothing new on the bus — an archive already fetches by digest, and the path
written is never the path executing.
Answers issue 142.
A host change merged yesterday reached no machine without a person copying a
file. The host is not a build target, no declaration delivers it, and the half
that recovers from a bad host — noticing the executable changed, a known-good
record, a launcher that rolls back — is written, tested and called by nothing.
All four machines run a byte-identical hand-copied binary that no package owns
and no record names, so nothing can say a machine is behind.
Found because ADR 0140 needs the machine to report a new fact, and merging that
could not roll it out.
jschoubben