Summary

The desktop app creates every new session with an explicit agent: "build" value, so default_agent from project config is never applied. A project whose default primary agent is a custom agent never gets it in desktop-created sessions.

Environment

• opencode version: 2.0.32 (bug also present in earlier desktop versions)
• OS: Windows_NT 10.0.26300 (win32 x64)
• Terminal: Unavailable: running via desktop app (no terminal env vars)
• Shell: C:\WINDOWS\system32\cmd.exe
• Install/channel: latest (desktop app, ai.opencode.desktop)
• Active plugins: none

Reproduction

1. In a project, set "default_agent": "my-agent" in opencode.jsonc and define .opencode/agents/my-agent.md with mode: primary.
2. Verify server-side: GET /api/config?location[directory]=<project> includes the config, and GET /api/agent?... returns my-agent with mode: "primary", hidden: false.
3. Create a session via the API with no agent field → session stores agent = NULL (default_agent path is available).
4. Create a new session from the desktop app UI.
5. Inspect the session (session_v2.agent in the DB): it is "build".

Expected Behavior

A new session with no explicit agent selection should use default_agent.

Actual Behavior

Desktop-created sessions store agent = "build" — the client passes the agent explicitly and bypasses default_agent. Every desktop session in this project got build; sessions created via opencode run --agent solution-architect correctly stored solution-architect.

Additional Context

• Reproduces consistently across desktop versions (observed on 2.0.31 and 2.0.32).
• Server-side config/agent discovery verified correct via API; the override happens at session creation in the client.
• Workaround used: a project file .opencode/agents/build.md redefines the built-in build agent with the desired persona so the hardcoded stamp still lands on the intended behavior.