Bug: on_message_async crashes on non-object JSON messages (e.g. heartbeats) #123

Description

WsClient.on_message_async crashes with AttributeError: 'str' object has no attribute 'get' when the WebSocket server sends a non-object JSON message (e.g. a string heartbeat).

Root Cause

The sync on_message method correctly handles raw string messages:

def on_message(self, ws, message):
    if isinstance(message, str):
        message = json.loads(message)
    message_type = message.get("type")

But the async on_message_async skips the type check after parsing:

async def on_message_async(self, ws, message):
    message = json.loads(message)
    message_type = message.get("type")  # crashes if json.loads returns a str

When the server sends a JSON string value (e.g. "heartbeat"), json.loads('"heartbeat"') returns "heartbeat" (a str), and str has no .get() method.

Impact

This causes run_async() to raise an unhandled AttributeError, disconnecting the WebSocket client. In a reconnect loop, this results in a permanent crash cycle with no useful work being done.

Suggested Fix

Add an isinstance check after json.loads, matching the pattern in on_message:

async def on_message_async(self, ws, message):
    if isinstance(message, str):
        message = json.loads(message)
    if not isinstance(message, dict):
        return
    message_type = message.get("type")
    ...

Environment

• lighter-sdk 1.0.3
• Python 3.12
• websockets (legacy async client)