An action on a name that is no app answers 404, not 'settings cannot be saved' (found walking capability map B2 on 9202)

Test TestAnActionOnANameThatIsNoAppIsA404 red first. Commit only.

controller/internal/api/router.go

@@ -771,6 +771,12 @@ func (r *Router) actionStack(w http.ResponseWriter, req *http.Request, action, n
 	// above, so nothing is recorded for an action that was never going to happen.
 	if desired, ok := desiredStateForAction(action); ok {
 		if derr := r.stackMgr.SetDesiredState(name, desired); derr != nil {
+			if errors.Is(derr, stacks.ErrStackNotFound) {
+				// no app by that name on this box (e.g. the bootstrap-managed controller): a 404, not a save failure
+				r.logger.Printf("[WARN] [api] %s for %s refused: no such app", action, name)
+				writeJSON(w, stackOpStatusFor(derr), apiResponse{OK: false, Error: r.errText(req, derr)})
+				return
+			}
 			r.logger.Printf("[ERROR] [api] %s for %s refused: could not record desired state: %v", action, name, derr)
 			writeJSON(w, http.StatusInternalServerError, apiResponse{
 				OK:    false,