fix: configure only the named app logger instead of mutating global root logger

Author: manascb1344

runner/logging.py

@@ -30,13 +30,15 @@ def format(self, record: logging.LogRecord) -> str:
 
 
 def setup_logging(level: int = logging.INFO) -> logging.Logger:
-    """Configure root logger with JSON formatter and return the app logger."""
-    handler = logging.StreamHandler()
-    handler.setFormatter(JsonFormatter())
+    """Configure app logger with JSON formatter without mutating global root logger."""
+    app_logger = logging.getLogger("modal-github-runner")
 
-    root_logger = logging.getLogger()
-    root_logger.handlers.clear()
-    root_logger.addHandler(handler)
-    root_logger.setLevel(level)
+    if not app_logger.handlers:
+        handler = logging.StreamHandler()
+        handler.setFormatter(JsonFormatter())
+        app_logger.addHandler(handler)
 
-    return logging.getLogger("modal-github-runner")
+    app_logger.setLevel(level)
+    app_logger.propagate = False
+
+    return app_logger