Validate Distributor endpoints before publication

internal/app/generation_test.go

@@ -311,6 +311,28 @@ func TestGenerateDetailedRejectsOverlongOutputBeforeWork(t *testing.T) {
 	}
 }
 
+func TestGenerateDetailedRejectsUnsupportedDistributorEndpointBeforeWork(t *testing.T) {
+	outputPath := filepath.Join(t.TempDir(), "daily.md")
+	cfg := generationDistributorConfig()
+	cfg.Notify.Distributor.Endpoint = "ftp://distributor.example.test"
+	bundle := generationBundle(t)
+	collector := &generationCollector{bundle: &bundle}
+	executor := &generationExecutor{}
+	notifier := &generationNotifier{}
+
+	result, err := GenerateDetailed(context.Background(), GenerateRequest{
+		Config: cfg, Report: ReportDaily,
+		Date: generationTime("2026-05-29T12:00:00-05:00"), Now: generationTime("2026-05-29T08:30:00-05:00"),
+		WorkingDir: t.TempDir(), OutputPath: outputPath, Collector: collector, Executor: executor, Notifier: notifier,
+	})
+	if err == nil || result == nil || collector.called || executor.promptInspections != 0 || executor.called || notifier.calls != 0 {
+		t.Fatalf("GenerateDetailed() result/error/collector/executor/notifier = %#v/%v/%t/%#v/%#v", result, err, collector.called, executor, notifier)
+	}
+	if _, statErr := os.Stat(outputPath); !os.IsNotExist(statErr) {
+		t.Fatalf("output exists after endpoint preflight failure: %v", statErr)
+	}
+}
+
 func TestGenerateDetailedReturnsResolvedResultWhenCollectionFails(t *testing.T) {
 	cfg := config.Defaults()
 	cfg.WeatherAPI.Timezone, cfg.Location.ID = "America/Chicago", "home"