Undeclaring gives a unit back the state it was found in, and removes a process the mesh made (hq ADR 0118, issue 130)

A service undeclared used to be stopped: unassigning the private network stopped the container
runtime, unassigning sshd would stop ssh, an uplink module would take the machine offline. The
host now records the unit's state when it first applies it and restores that on undeclare —
found running stays running; started by the mesh (the converge filter) is stopped again; nothing
is started on the way out; a pre-existing record leaves the unit alone.

An undeclared process had no removal at all and failed every apply on its node; its unit, timer
and bundle are now removed.

internal/apply/plan.go

@@ -80,8 +80,17 @@ func Plan(d *declaration.Declaration, known store.State, origin string) []Step {
 	for _, orphan := range known.Orphans(declared, origin) {
 		step := Step{Verb: "remove", Type: orphan.Type, ID: orphan.ID, Target: orphan.Target,
 			Why: "recorded here and no longer declared"}
-		if orphan.Stateless {
+		switch {
+		case orphan.Stateless:
 			step.Verb, step.Why = "forget", "no longer declared; its unit's state was never the mesh's and is left as it is"
+		case orphan.Type == string(declaration.TypeService):
+			// What removal will do, said before it does it (novox/hq ADR 0118): a unit is given
+			// back what the host found, so the preview names which units that stops.
+			if f := orphan.Found; f != nil && (f.State == "stopped" || f.Boot == "disabled") {
+				step.Verb, step.Why = "restore", "no longer declared; the mesh started or enabled it, and it goes back as it was found"
+			} else {
+				step.Verb, step.Why = "forget", "no longer declared; the unit is the machine's and is left as it is"
+			}
 		}
 		if d.Adoption == nil && strings.HasPrefix(orphan.ID, declaration.AdoptionPrefix) {
 			step.Why = "what protected this node while adopted; removed last, once everything else applied"