TypeError: StreamReader.readline() got an unexpected keyword argument 'max_line_length' when streaming with aiohttp

[SeleneXX]

Environment details
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• Programming language: Python
• OS: Windows
• Language runtime version: 3.13.3
• Package version: google-genai 2.5.0, aiohttp 3.13.3
Steps to reproduce
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1. Install google-genai and aiohttp in the same environment:
   pip install google-genai==2.5.0 aiohttp==3.13.3

2. Run any async streaming request:
   import asyncio
   from google import genai

   async def main():
   client = genai.Client(api_key="YOUR_API_KEY")
   async for chunk in client.aio.models.generate_content_stream(
   model="gemini-3.5-flash",
   contents="Hello"
   ):
   print(chunk)

   asyncio.run(main())

3. The request crashes immediately with:
   TypeError: StreamReader.readline() got an unexpected keyword argument 'max_line_length'
   Root cause
   ──────────

In google/genai/_api_client.py around line 450, the library calls:

line_bytes = await self.response_stream.content.readline(
max_line_length=READ_BUFFER_SIZE
)

However, aiohttp.StreamReader.readline() does not accept any parameters. Its signature is simply:

async def readline(self) -> bytes:
return await self.readuntil()

The max_line_length keyword argument was introduced in PR #2437, but it is incompatible with the actual aiohttp API.

The line-length limit is already governed by the limit parameter of StreamReader,
which is set correctly via read_bufsize=READ_BUFFER_SIZE (4MB) when the aiohttp
ClientSession is created:
https://github.com/googleapis/python-genai/blob/main/google/genai/_api_client.py#L958

Suggested fix
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Remove the unsupported max_line_length keyword argument:

line_bytes = await self.response_stream.content.readline()

The existing read_bufsize configuration already prevents LineTooLong errors for large SSE lines.