fix(packaging): an upgrade must not stop and disable the agent — 0.1.9

dpkg calls the OLD package's prerm on an UPGRADE as well as on a removal (rpm passes a
remaining-instance count), and preremove.sh ran `systemctl disable --now monky-deployd.timer`
unconditionally. Upgrading env-dev-01 and env-dev-08 to 0.1.8 today stopped and disabled both
agents.

The failure is silent, which is the dangerous part: the box stays reachable, the containers keep
running, and nothing reports that check-ins have ceased — the backend just stops converging. A
fleet upgrade would have taken every agent offline at once and looked like a success.

preremove.sh now returns early for every upgrade shape (upgrade, failed-upgrade, deconfigure,
rpm's 1) and only disables on a real removal. postinstall.sh try-restarts the long-lived proxy
unit so it picks up the new code; the timer needs nothing, since each tick is a fresh process.

Tests drive the script with a fake systemctl on PATH and assert an upgrade touches no units.
OPERATIONS.md warns that a box coming FROM 0.1.8 or earlier still needs its timer re-enabled by
hand, because the old prerm has already run by then.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KLB7jieMNRkTsJ2epr4Ds1

monky_deployd/__init__.py

@@ -4,4 +4,4 @@ Dials monky-tenancy over the mesh with the box's host identity, fetches the rend
 leases a deploy grant, logs in to OpenBao, reads its own secrets, runs `docker compose`,
 reports. Stdlib only; the optional `openziti` SDK is the `sdk` transport."""
 
-__version__ = "0.1.8"
+__version__ = "0.1.9"