refactor: improve X402Auth streaming stability and schema filtering

[lofingv]

Description

This PR refactors the X402Auth handler to ensure better reliability during streaming requests and aligns the implementation with the documented arguments.

Key Changes:

• Streaming Stability: Added request.read() before the initial request. This ensures that the request body can be re-read if a 402 challenge occurs, preventing StreamConsumed errors during LLM streaming or large POST requests.
• Schema Filtering: Added the missing scheme_filter argument to __init__ to match the existing docstring documentation and improve payment selection flexibility.
• Robustness: Added a safety check for selected_requirements. If no compatible payment method is found, it now logs an error and returns gracefully instead of potentially failing downstream.
• Improved Error Logging: Updated exception handling to provide clearer string representation of errors.

Testing:

• Verified that the httpx.Auth flow correctly handles 402 responses without losing the original request context.

[Copilot]

Pull request overview

This PR improves the X402Auth authentication handler by addressing streaming reliability issues and aligning the implementation with its documented interface. The changes ensure that request bodies can be re-read during 402 payment challenges, preventing StreamConsumed errors in streaming scenarios.

Changes:

• Added request.read() to buffer request bodies before initial submission, enabling re-reading after 402 responses
• Added missing scheme_filter parameter to match documented API
• Simplified type hints for the payment requirements selector callback
• Added validation to handle cases where no compatible payment method is found

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[lofingv]

Updated types with a Type Alias and fixed scheme_filter usage as suggested by Copilot. Ready for review

[adambalogh]

Thanks!

[lofingv]

Updated the PR to match the new project structure. The x402_auth.py has been moved to the client/ folder, and I've also implemented the scheme_filter and improved type safety with PaymentSelector as we discussed.

[lofingv]

Thanks!

No problem at all! I'm really enjoying the project, so happy to jump in and help whenever I can.