A default naming a route the Models page has since removed left the
composer saying 选择模型 while the input still accepted a message, which
then failed inside the adapter mid-turn.
`session.prompt` now refuses with `model-unavailable` before opening a
turn. That is the enforcement boundary: the method stays callable no
matter what a client disables. `session.models` reports the same fact as
`routable`, and ui-model pushes a block through the new
`ctx.conversation.blocks` registry so the bar renders the disabled
textarea it already renders without a workspace, carrying the blocker's
own reason. The push direction is forced — ui-model already depends on
ui-conversation, so ui-conversation cannot read it back.
The gate is `routable`, not "matches no advertised group": catalog
membership is advisory, so a route serving a model it stopped advertising
is missing from the groups yet perfectly usable, and `null` before the
first load never blocks so a slow Host cannot lock a working composer.
The scaffold gains a route-only adapter for fixture-less keyless
scenarios. Registering zero providers is a test artifact — every product
composition mounts one — and the goldens that froze the seat's fallback
label now show the model those scenarios actually route to.
- ui-model README pair (short-form Model Experience + audited registry
entry + Known Limitations), recorded in the pairing manifest
- llm-deepseek README pair rebased onto master's version with this PR's
real deltas (friendly names, 256k, selector consumers) on both sides;
runtime/ui-conversation READMEs revert to master (their sections
documented the removed Session state machine and control slot)
- config catalog regenerated for the ui-model roster row
- ModelDirectory.store JSDoc; ui-model files join the TODO(gui) coverage
deferral lane beside their ui-command/ui-slash siblings
