Refactor single-input config path normalization helpers

internal/config/config_test.go

@@ -692,6 +692,25 @@ func TestNewTrimConfigAcceptsOutputSchemaOverride(t *testing.T) {
 	}
 }
 
+func TestNewTrimConfigTreatsWhitespaceReportFileAsOmitted(t *testing.T) {
+	dir := t.TempDir()
+	input := writeTempFile(t, dir, "input.json")
+	output := filepath.Join(dir, "trimmed.json")
+
+	cfg, err := NewTrimConfig(TrimOptions{
+		InputFile:  input,
+		OutputFile: output,
+		Keep:       "1",
+		ReportFile: "  \t  ",
+	})
+	if err != nil {
+		t.Fatalf("config failed: %v", err)
+	}
+	if cfg.ReportFile != "" {
+		t.Fatalf("report file = %q, want empty", cfg.ReportFile)
+	}
+}
+
 func TestNewTrimConfigRejectsInvalidOutputSchemaOverride(t *testing.T) {
 	dir := t.TempDir()
 	input := writeTempFile(t, dir, "input.json")
@@ -812,6 +831,25 @@ func TestNewNormalizeConfigRejectsUnknownOutputModule(t *testing.T) {
 	}
 }
 
+func TestNewNormalizeConfigTreatsWhitespaceReportFileAsOmitted(t *testing.T) {
+	dir := t.TempDir()
+	input := writeTempFile(t, dir, "input.json")
+	output := filepath.Join(dir, "normalized.json")
+
+	cfg, err := NewNormalizeConfig(NormalizeOptions{
+		InputFile:     input,
+		OutputFile:    output,
+		ReportFile:    "\n\t ",
+		OutputModules: DefaultOutputModules,
+	})
+	if err != nil {
+		t.Fatalf("config failed: %v", err)
+	}
+	if cfg.ReportFile != "" {
+		t.Fatalf("report file = %q, want empty", cfg.ReportFile)
+	}
+}
+
 func assertPositiveFloatEnvValidation(t *testing.T, envName string) {
 	t.Helper()