Implemented an overlap detection module in the postprocessing chain

internal/config/config.go

@@ -137,6 +137,7 @@ func normalizeInputFiles(paths []string) ([]string, error) {
 	}
 
 	normalized := make([]string, 0, len(paths))
+	seen := make(map[string]struct{}, len(paths))
 	for _, path := range paths {
 		path = strings.TrimSpace(path)
 		if path == "" {
@@ -147,6 +148,10 @@ func normalizeInputFiles(paths []string) ([]string, error) {
 		if err := requireFile(clean, "--input-file"); err != nil {
 			return nil, err
 		}
+		if _, exists := seen[clean]; exists {
+			return nil, fmt.Errorf("duplicate --input-file %q", clean)
+		}
+		seen[clean] = struct{}{}
 		normalized = append(normalized, clean)
 	}
 	sort.Strings(normalized)