[V2] xAI: Responses WebSocket fails after tool calls

[mrodhansen]

Description

xAI sessions fail after the first tool call when Responses WebSockets are enabled. The initial response and tool execution succeed, but OpenCode's incremental response.create includes both instructions and previous_response_id.

xAI rejects that combination, then OpenCode masks the provider error as Invalid xAI Responses WebSocket event because xAI's error envelope has no top-level type.

A pass-through WebSocket probe captured:

{"error":{"message":"Request validation error: Argument not supported: instructions and previous_response_id together","type":"api_error"}}

This reproduces consistently on beta-19398 and dev-19405. dev-19390 passes and dev-19391 is the first failing published build, corresponding to #48140 (bdc143c1d5caa9571106233dd3014242f5c126ec), which enabled Responses WebSockets by default.

Expected: the tool result is sent and the model completes the response.

Actual: the continuation aborts with the generic WebSocket event error.

Disabling xAI WebSockets makes the identical request pass:

{"providers":{"xai":{"websocket":false}}}

Plugins

None configured

OpenCode version

0.0.0-beta-19398
Also reproduced on 0.0.0-dev-19405

Steps to reproduce

1. Authenticate the xAI provider and use xai/grok-4.6 with the default WebSocket setting.
2. Run:

   opencode2 run --standalone --model "xai/grok-4.6" -- "Run pwd with the shell tool, then reply with exactly DONE"

3. The tool succeeds, then the continuation fails with:

   Invalid xAI Responses WebSocket event
   

Screenshot and/or share link

Not provided; the minimal standalone reproduction above is consistent.

Operating System

macOS 26 / Darwin 25.6.0 (arm64)

Terminal

WezTerm (TERM=xterm-256color)