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/unknown_stack_action_test.go

@@ -0,0 +1,29 @@
+package api
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+// Found walking the capability map's B2 („App lifecycle") on 9202, 2026-10-28 night: a Stop of a name that is no app
+// on this box (`felhom-controller` — bootstrap-managed, not a stack) answered 500 „…az alkalmazás beállításai nem
+// menthetők." — the desired-state write's „not found" read as a save failure. It is a 404 now, before any intent is
+// recorded. RED-PROOF: drop the ErrStackNotFound branch in actionStack → 500 → FAILS.
+func TestAnActionOnANameThatIsNoAppIsA404(t *testing.T) {
+	r, _, _, _ := newSlice4Router(t)
+	for _, action := range []string{"stop", "start"} {
+		w := httptest.NewRecorder()
+		r.actionStack(w, httptest.NewRequest("POST", "/api/stacks/nosuchapp/"+action, nil), action, "nosuchapp")
+		var resp apiResponse
+		_ = json.Unmarshal(w.Body.Bytes(), &resp)
+		if w.Code != http.StatusNotFound {
+			t.Fatalf("%s of a name that is no app: %d %q — want 404", action, w.Code, resp.Error)
+		}
+		if strings.Contains(strings.ToLower(resp.Error), "mentheto") || strings.Contains(resp.Error, "menthetők") {
+			t.Fatalf("%s: the answer still blames a save: %q", action, resp.Error)
+		}
+	}
+}