Say in the plan that a unit is restored only if it is still as the mesh held it

Confirmation pass of #66: the plan is a preview, and the removal reads the unit when it runs; a masked
unit or one changed since is left as it is.

internal/apply/giveback_test.go

@@ -97,7 +97,8 @@ func TestThePlanSaysAStoppedUnitIsStartedAgain(t *testing.T) {
 			said = s.Verb + ": " + s.Why
 		}
 	}
-	if !strings.HasPrefix(said, "restore: ") || !strings.Contains(said, "started and enabled at boot again") {
+	if !strings.HasPrefix(said, "restore: ") || !strings.Contains(said, "restore if still as the mesh held it") ||
+		strings.Contains(said, "so it is started") {
 		t.Errorf("the plan says %q", said)
 	}
 }

internal/apply/plan.go

@@ -135,8 +135,10 @@ func Plan(d *declaration.Declaration, known store.State, origin string) []Step {
 				if f.Boot == "enabled" && orphan.Declared.Boot == "disabled" {
 					back = append(back, "enabled at boot")
 				}
-				step.Verb, step.Why = "restore", "no longer declared; the host found it running and enabled and "+
-					"the mesh held it stopped, so it is "+strings.Join(back, " and ")+" again"
+				// A preview: whether it is still as the mesh held it is read when the removal runs, and a
+				// masked unit or one changed since is left as it is.
+				step.Verb, step.Why = "restore", "no longer declared; restore if still as the mesh held it: "+
+					strings.Join(back, " and ")+" again, as the host found it, unless it is masked or was changed since"
 			case f.State == "stopped" || f.Boot == "disabled":
 				var back []string
 				if f.State == "stopped" {