nff: handle errors and exit appropriately in linter

src/main.rs

@@ -351,6 +351,8 @@ fn process_lint_command(
     };
 
     let is_multiple_files = files.len() > 1;
+    let mut has_errors = false;
+    
     for file_path in files {
         if let Err(e) = process_single_file_lint(
             &file_path,
@@ -364,12 +366,18 @@ fn process_lint_command(
             is_multiple_files,
         ) {
             eprintln!("Error processing {}: {}", file_path, e);
+            has_errors = true;
             if !is_multiple_files {
                 return Err(e);
             }
         }
     }
 
+    // Exit with non-zero code if any file had errors
+    if has_errors {
+        std::process::exit(1);
+    }
+
     Ok(())
 }
 
@@ -459,9 +467,9 @@ fn process_single_file_lint(
         println!("{}", diagnostics.to_human_readable());
     }
 
-    // Exit with non-zero code if there are errors
+    // Return error if there are diagnostics errors
     if diagnostics.has_errors() {
-        std::process::exit(1);
+        return Err(anyhow::anyhow!("Diagnostics found errors in file"));
     }
 
     Ok(())