description: "Model selection for the Web GUI: the /model popup and the composer model seat over one per-session provider-grouped directory; for users and maintainers of model routing."
This package provides model selection in the Web GUI: the `/model` popup command and the composer's model seat, both over one per-session directory of provider-grouped models. Choosing a model submits the complete selection — provider, model, and reasoning effort — which the Host snapshots at the next prompt-assembly boundary, so the following request uses it while a running step keeps its assembled selection. The composer seat shows a two-level Model/Effort menu: models stay provider-grouped, and the selected exact model supplies its adapter-owned effort names and default. When the Host reports that no adapter serves the session's route, the composer input goes inert until a route becomes available.
## Table of Contents
- [Use this package](#use-this-package)
- [Understand the implementation](#understand-the-implementation)
- [Further Exploration](#further-exploration)
- [Model Experience](#model-experience)
- [Known Limitations and Deferred Work](#known-limitations-and-deferred-work)
- [Dev Note](#dev-note)
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## Use this package
Mount this plugin alongside `ui-conversation` and the commands package; the composer then shows the model seat next to the pending indicator, and `/model` opens the same directory as a popup. Both surfaces show the host-reported current selection when the exact provider/model pair remains in the advertised groups; a missing catalog row leaves the routable selection intact while the trigger prompts `Select model`.
### Model and effort
Models stay grouped by provider. The menu shows model and effort names only; catalog descriptions remain available to other consumers. The `/model` popup applies the selected model's default effort; the composer can then choose any advertised effort. An adapter without reasoning metadata leaves the Effort row absent; there is no arbitrary effort input.
### Unroutable sessions
When the Host reports that no adapter serves the session's route, this plugin raises a composer block and the input goes inert with its own copy; recovering clears it without a reload. A `null` before the first load or after one failed never blocks, and catalog membership never blocks either — a route serving a model it does not advertise is missing from the groups yet usable.
Two entries over ONE per-session directory owned by `ModelDirectoryResolver` (`ctx.modelDirectories`): the `/model` popupSelect contribution (registered through `ctx.commandUi`) and the composer's named `conversation.input.model` seat both load the session's advisory directory through `session.models` and submit through `session.selectModel` via the same `ModelDirectory` instance, so a switch made in either entry is what the other shows next. Directory loads and selections share a generation counter so an older response never overwrites a newer one; a connection reset drops every resident projection and repulls the Host-restored selection. Directories are per-session, resolved lazily, and disposed with the session scope; addressed subagent sessions expose neither entry. Every resident directory refetches directly on forwarded `llm/adapters-updated` and `settings/document-updated` owner events.
Indirectly, through the `session.selectModel` selection both entries submit: the Host snapshots the complete `ModelSelection` at the next prompt-assembly boundary and owns the model-visible effect, while a running step keeps its assembled selection.
- **No create-time or addressed-subagent selection** — both entries require an existing ordinary session's Agent; there is no draft-phase model choice to fold into session creation, and subagent continuation deliberately exposes no independent model-selection contract.
- **Directory names are presentation-only** — selection and persistence use provider/model/effort ids; a provider whose catalog or exact-model metadata lookup fails lists as an unselectable failure row until reload.
- **No arbitrary effort input** — the composer offers only the exact model's adapter-advertised levels; an adapter without reasoning metadata leaves the Effort row absent.
**Runtime invariant:** No companion is published. A single command contribution registration whose disposal is proven by the HMR-safety spec — it emits no cordis events and owns no cross-plugin mutable state.
