feat(openai): add session-scoped Responses WebSocket transport

[danielkov]

Summary

Add opt-in WebSocket transport to the OpenAI Responses provider, with session-scoped connection reuse and shared HTTP/WebSocket response decoding. Bump agentkit-provider-openai from 0.10.9 to 0.10.10.

Impact

HTTP/SSE remains the default. Applications can select WebSocket or Auto through OpenAIResponsesConfig::with_transport; Auto switches the session to HTTP after a handshake HTTP 426.

Technical details

Connection lifecycle and retry safety

Each session permits one active WebSocket turn and returns a completed connection for reuse. Cancellation, unfinished-turn drop, interrupted authentication refresh, and protocol failures discard the connection. Authentication remains credential-bound; requests with ambiguous delivery or accepted responses are not automatically replayed.

Shared response semantics

Both transports use the existing response event decoder, preserving tool calls, reasoning, images, usage, and continuation validation. WebSocket requests use flattened response.create messages without HTTP-only stream or background fields. Message limits and deadline handling bound transport work.

Initial scope

Requests still send the full transcript; incremental previous_response_id delivery is deferred until lossless prefix compatibility can be established. WebSocket upgrades use a dedicated reqwest HTTP/1 client and the existing TLS stack; custom Http clients continue to apply only to HTTP/SSE.