ADR 0141: the host delivers its own successor, and versions live side by side

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.

02-DECISIONS/README.md

@@ -221,6 +221,7 @@ python3 00-META/checks/index.py            fail if stale
 - **0138** — [An assignment binds an endpoint and says how far it reaches](0138-an-assignment-binds-an-endpoint-and-says-how-far-it-reaches.md)
 - **0139** — [A network is forwarded because a module declared it](0139-a-network-is-forwarded-because-a-module-declared-it.md)  *(superseded)*
 - **0140** — [The filter constrains what arrives from outside, and says nothing about a machine's own guests](0140-the-filter-constrains-what-arrives-from-outside.md)
+- **0141** — [The host delivers its own successor, and versions live side by side](0141-the-host-delivers-its-own-successor.md)
 
 ### How it is built