fix(codeagent): validate non-empty output message before printing

Return exit code 1 when backend returns empty result.Message with exit_code=0.
Prevents silent failures where no output is produced.

Generated with SWE-Agent.ai

Co-Authored-By: SWE-Agent.ai <noreply@swe-agent.ai>

codeagent-wrapper/internal/app/cli.go

@@ -648,6 +648,12 @@ func runSingleMode(cfg *Config, name string) int {
 		return result.ExitCode
 	}
 
+	// Validate that we got a meaningful output message
+	if strings.TrimSpace(result.Message) == "" {
+		logError(fmt.Sprintf("no output message: backend=%s returned empty result.Message with exit_code=0", cfg.Backend))
+		return 1
+	}
+
 	fmt.Println(result.Message)
 	if result.SessionID != "" {
 		fmt.Printf("\n---\nSESSION_ID: %s\n", result.SessionID)

codeagent-wrapper/internal/app/main_test.go

@@ -1913,6 +1913,37 @@ func TestRun_PassesReasoningEffortToTaskSpec(t *testing.T) {
 	}
 }
 
+func TestRun_NoOutputMessage_ReturnsExitCode1AndWritesStderr(t *testing.T) {
+	defer resetTestHooks()
+	cleanupLogsFn = func() (CleanupStats, error) { return CleanupStats{}, nil }
+	t.Setenv("TMPDIR", t.TempDir())
+
+	selectBackendFn = func(name string) (Backend, error) {
+		return testBackend{name: name, command: "echo"}, nil
+	}
+
+	runTaskFn = func(task TaskSpec, silent bool, timeout int) TaskResult {
+		return TaskResult{ExitCode: 0, Message: ""}
+	}
+
+	isTerminalFn = func() bool { return true }
+	stdinReader = strings.NewReader("")
+
+	os.Args = []string{"codeagent-wrapper", "task"}
+
+	var code int
+	errOutput := captureStderr(t, func() {
+		code = run()
+	})
+
+	if code != 1 {
+		t.Fatalf("run() exit=%d, want 1", code)
+	}
+	if !strings.Contains(errOutput, "no output message") {
+		t.Fatalf("stderr missing sentinel error text; got:\n%s", errOutput)
+	}
+}
+
 func TestRunBuildCodexArgs_NewMode(t *testing.T) {
 	const key = "CODEX_BYPASS_SANDBOX"
 	t.Setenv(key, "false")