tui: bindable "set as default model for this agent" action in model dialog

[abran-labs]

Summary

The model dialog (/models) supports ctrl+f to favorite a model, but there is no way to persist a model as the default for an agent from the UI. Setting an agent default — including for subagent-mode agents — currently requires hand-editing opencode.json(c) or agent Markdown frontmatter.

Environment

• opencode version: 0.0.0-beta-19157
• OS: Linux 7.1.6-arch1-1 (x64)
• Terminal: ghostty (xterm-ghostty, truecolor)
• Shell: /usr/bin/bash
• Install/channel: beta
• Active plugins: omo-v2 (local), local TUI plugins under ~/.config/opencode/plugins/tui

Reproduction

1. Open /models in the TUI and highlight a model.
2. Press ctrl+f — favorite toggles.
3. Look for a "set as default" action — none exists.

Expected Behavior

A bindable action in the model dialog (e.g. ctrl+d) that sets the highlighted model as the default model for the current agent — equivalent to writing agents.<id>.model in config. Ideally this also works for subagent-mode agents, e.g. reachable from the agent list or a child-session view, since subagent models are otherwise only configurable by editing config files by hand. Subagents that have no configured model silently inherit the parent session model, so there is currently no UI surface at all for controlling what model a subagent runs on.

Actual Behavior

No such action exists. Switching an agent's default model requires manually editing agents.<id>.model in opencode.json(c) or the agent's frontmatter.

Additional Context

/models on a primary session only changes that session's model; it does not persist a per-agent default. As a workaround I built a local TUI plugin with its own agent→model picker dialog that writes agents.<id>.model (format-preserving JSONC edit). The missing built-in pieces are:

1. A "set as default for this agent" action in the model dialog.
2. Agent context in that action so it can target subagents, not just the current primary agent.

[abran-labs]

Framing clarification after looking at the keybind architecture: this doesn't require hardcoding a key. The model dialog already exposes remappable command IDs (model.dialog.favorite, model.dialog.provider), so the request reduces to a single new command — e.g. model.dialog.set_default — that persists the highlighted model as agents.<current-agent>.model in config. Binding it to ctrl+d (or anything else) is then just a keybinds entry in cli.json, same as every other action.

On the "already possible via config" close given to #11209: true for primary agents, and technically true for subagents via agents.<id>.model. But subagent models have no UI surface at all — they aren't shown while running (#38495, #41172, #42367), and the resolution rule (no configured model → inherit parent session model) is silent. Favorites are one keypress in the dialog; agent defaults are hand-edited JSONC. One new command ID closes that gap.

Related: #38495 #41172 #42367

[abran-labs]

Scope addition after further testing: built-in slash commands cannot be removed or shadowed cleanly, and plugin commands cannot safely take a built-in command id.

Concrete case: a TUI plugin registers a command with slash: { name: "agents" }. The built-in agent.list ("Switch agent") owns that slash name:

• Registering a plugin command with the same id (agent.list) is silently dropped — the built-in wins and the plugin command disappears.
• keybinds: { "agent.list": "none" } in cli.json removes the keybind but the slash entry remains.
• The plugin disable prefix (-) applies to plugins, not built-in commands.

Partial workaround found: keymap layers sort by priority, so a plugin layer with priority > 0 lists its same-named slash command above the built-in, making it the default selection in autocomplete. But the built-in entry remains visible below, and there is no way to remove it.

Requests: (1) allow plugin commands to override built-in command ids instead of being silently dropped, and/or (2) a config surface to hide built-in slash commands. Would fix this request and general TUI customization.

[argszero]

I'd like to work on this.

This is a clean, well-scoped TUI feature in packages/app. I've scoped the implementation surface on the v2 branch and confirmed it's feasible:

• The model dialog (packages/app/src/providers/models/select-dialog.tsx) already wires a keybinding path and exposes a model selection flow — a new bindable action can hook in the same way ctrl+f favorite is handled (handleDocumentSearchKeydown / the dialog's own keydown handler).
• Agent context for targeting a non-primary agent is reachable via the existing agent controls in packages/app/src/composer/model.ts (agents.controls().agents.options / .current), which already surfaces per-agent selection for mentions and model prompt.
• Persisting agents.<id>.model needs a config write path; I'll follow the format-preserving JSONC-edit approach used elsewhere in the TUI rather than re-serializing the config.

Both the primary-agent default and the subagent-mode agent default (the harder part — subagents silently inherit the parent session model today) are in scope.

I'll base the work on v2 (per this repo's AGENTS.md) and open a PR once it's implemented and tested.