ACP Buffer Limit Issue

[OhadRubin]

Hey, I encountered the following issue while using the sdk:

spawn_stdio_transport was crashing with this error:

asyncio.exceptions.LimitOverrunError: Separator is found, but chunk is longer than limit

After digging into it, I figured out what's happening. The SDK uses newline-delimited JSON-RPC over asyncio streams, and asyncio has a default 64KB buffer limit for line-based operations. When messages get larger than that, everything explodes.

The issue is that:

• The ACP SDK creates asyncio.StreamReader without specifying a limit parameter
• This means it defaults to 64KB
• There's no way to configure this in the SDK - it's just hardcoded to use the default

What I ended up doing is that I implemented my own version of spawn_stdio_transport and set the limit explicitly when creating the subprocess:

process = await asyncio.create_subprocess_exec(
    ...,
    limit=10 * 1024 * 1024  # 10MB buffer limit
)

This works fine for my use case.

If you're asking me, you should expose limit as a parameter in both:

• spawn_stdio_transport() - for subprocess-based agents
• stdio_streams() - for agents reading their own stdio