tui: default_agent is ignored on startup in V2 #37225

Summary

The OpenCode V2 full TUI ignores default_agent when starting a new session and selects Build instead. This occurs with both built-in and custom primary agents.

Environment

• opencode version: opencode2 v0.0.0-next-15636
• OS: Linux 7.1.2-arch3-1, x86_64
• Terminal: tmux (TERM_PROGRAM=tmux, TERM=xterm-256color, COLORTERM=truecolor)
• Shell: /bin/zsh
• Install/channel: next
• Active plugins: None in the clean reproduction. The normal environment has local goal-mode and tmux-status plugins, but the issue was reproduced with an isolated XDG_CONFIG_HOME and all plugins disabled.

Reproduction

1. Start the full TUI with an isolated configuration and the built-in plan agent configured as the default:

   XDG_CONFIG_HOME=/tmp/opencode-clean \
     OPENCODE_CONFIG_CONTENT='{"default_agent":"plan","plugins":["-*"]}' \
     opencode2 --standalone

2. Type any text in the prompt so the selected agent appears in the status line.

3. Observe that the status line shows Build.

The issue also reproduces with a custom primary agent:

{
  "default_agent": "full",
  "agents": {
    "full": {
      "description": "Build without permission prompts",
      "mode": "primary",
      "permissions": [
        { "action": "*", "resource": "*", "effect": "allow" }
      ]
    }
  }
}

Expected Behavior

The full TUI should initially select the agent configured by default_agent. With the minimal reproduction it should start in Plan; with the custom configuration it should start in full.

Actual Behavior

The full TUI always starts in Build. The agent catalog is returned with Build first, and the TUI selects that first entry instead of the configured default.

Additional Context

• Reproduces consistently.
• Reproduces with the built-in plan agent, so it is not specific to custom agents.
• Reproduces with all plugins disabled and isolated global configuration.
• Restarting the shared OpenCode service does not help.
• Creating a session through the API with agent: "full" and opening it using opencode2 --session <id> still initializes the TUI selector to Build.
• opencode2 mini --agent full selects the requested agent, but changes to the minimal interface and is not a workaround for the full TUI.
• Immediate manual workaround: press Shift+Tab after startup when the desired custom agent is the last catalog entry.