feat: Increase default stdio buffer limit and allow configuration

[jacoblee93]

Summary

The default stdio stream buffer size is only 64kb, which means you get errors like this when trying to send messages larger than that via ACP:

Filesizes above that are quite common for multimodal data

The new default of 50MB should handle most practical multimodal cases. Definitely open to tweaking this default though if anyone has strong feelings! And it's now configurable if needed

Related issues

Testing

Added tests and ran appropriate make commands

Docs & screenshots

Not sure how to best document, assuming this will automatically propagate to API refs?

Checklist

• Conventional Commit title (e.g. feat:, fix:).
• Tests cover the change or are not required (explain above).
• Docs/examples updated when behaviour is user-facing.
• Schema regenerations (make gen-all) are called out if applicable.

[PsiACE]

Thanks for your PR. The default 50MB limit doesn't seem reasonable. I think it's sufficient to just allow it to be configured.

[phil65]

@PsiACE I would at least increase the default limit to at least 1MB or sth.. its quite easy to reach the 64kb when it comes to sending the models and slash commands (model lists can easily reach 1000 items for some agents)

[PsiACE]

thanks @phil65, i will merge it first and consider a small and enough default value. and cc @stdrc for suggestion

[jacoblee93]

Thank you! Yeah 50MB is probably more than needed outside of niche cases. I've seen some screenshots around 5MB though so wouldn't go too small.

[PsiACE]

Thank you! Yeah 50MB is probably more than needed outside of niche cases. I've seen some screenshots around 5MB though so wouldn't go too small.

talked with stdrc, i will keep 50MB as default