opencode ACP from Xcode 27 beta 2 uses default model big-pickle ignoring opencode.json or model selected in TUI

[velouria]

Description

On macOS 27 beta 2 (26A5368g) configure opencode 1.17.11 custom ACP agent in Xcode 27 beta 2 (27A5209h). Set up opencode with opencode.json specifying the model to be used served from LMStudio (same issue occurs with ollama).
When prompting from Xcode, opencode rather than using the specified model and LMStudio (or ollama) it always uses big-pickle. opencode never connects to LMStudio or ollama.

Plugins

None

OpenCode version

1.17.13

Steps to reproduce

1. configure opencode 1.17.13 on macOS 27. Set up opencode.json to connect to LMStudio/ollama with the model to be used.
2. run opencode cli and in the TUI select the model to be used (if not already selected). It seems that it needs to be running in order to be used by Xcode.
3. configure Xcode 27 beta custom agents to use opencode in Xcode Settings > Intelligence > Add an Agent…

4. In Xcode enter a prompt and check opencode logs located at ~/.local/share/opencode/log/opencode.log notice that the the session and subsequent messages are for model.id=big-pickle model.providerID=opencode
5. It seems that opencode ACP never reads the opencode.json configuration. Also there is no way to pass arguments to specify the provider and/or the model to be used.

Screenshot and/or share link

No response

Operating System

macOS 27 beta 2 (26A5368g)

Terminal

macOS Terminal.app

Regression

Might be related to: #13644

*edited version number as it reproduces in 1.17.13

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Bug: REST API session model ignored when loading session via ACP #27645: ACP session model is ignored and replaced with defaultModel() — very similar root cause where ACP does not respect the configured/stored model
• ACP: session/set_mode does not activate the agent's configured model #18620: ACP session/set_mode does not activate the agent's configured model from opencode.json
• [Bug] ACP-Next does not remember last selected model when creating new chat in JetBrains IDEA #30047: ACP integration does not remember the last selected model (new sessions reset to default)

If your issue is distinct (e.g., specific to the Xcode 27 ACP integration path), please let us know and a maintainer will triage further.

[velouria]

The issue is different in the sense that there was not a previous session configured, the provider and model were set in the configuration and also in the TUI but were ignored and defaulted to opencode and big-pickle.
It might have the same root cause as the issues above but it's not clearly a dupe.

[TheRegent76]

same issue using the steps you described. This issue has been 'fixed' before, but still persists.

[TheRegent76]

This is what I found concerning the fix that doesn't seem to be working: #4006