fix(ui-models): three faults the running app surfaced

**A hand-declared route must not offer a reasoning effort.** The earlier
commit read the create card's missing control as drift and added one. It
is the other way round: such a model has no reasoning capability — pi-ai's
installed catalog is what supplies one, and it ships nothing under the
route — so `resolveModel` throws UNSUPPORTED_REASONING_EFFORT for every
model on it and the whole provider drops out of the picker. Verified
against the adapter, not inferred. The create card no longer offers it and
the editor withholds it on the directory's `declared` bit, which is the
real bug: that control has always been wrong for these routes.

**A blocked composer locked the way out of the block.** Reusing the
no-workspace inert posture disabled the model seat along with everything
else, so the bar asked for a model while preventing the one control that
picks one. A block now rides its own `blocked` owner prop: the textarea,
send, commands, plan seat, and access chip all lock, and the model seat
alone stays live.

**A Provider ID could derive an illegal credential reference.** The card
accepted a digit-leading id, whose derived `123_API_KEY` then failed at
the credential seam with a raw regular expression the user cannot act on.
The id must now start with a letter, and a test pins the relation between
the two rules rather than the regex.

packages/client/ui-conversation/src/client/contract/slots.ts

@@ -265,6 +265,14 @@ export interface ConversationSessionHeaderInjected {
 export interface ComposerBarOwnerProps {
   /** Hero = empty-state centered card; composer = resident bottom bar. */
   variant: 'hero' | 'composer'
+  /**
+   * A block another plugin raised for this session: the bar refuses input and
+   * shows the blocker's reason as the placeholder, but — unlike `disabled` —
+   * keeps the model seat live. Every block this contract has is one the user
+   * clears by choosing a model, so locking that seat too would leave the
+   * composer telling them to do the one thing it prevents.
+   */
+  blocked?: { readonly reason: string }
   /**
    * Inert no-workspace state: the bar renders its normal DOM fully disabled
    * (textarea, add, send) so the workspace pick transitions in place instead

packages/client/ui-conversation/src/client/skeleton/ConversationRoot.tsx

@@ -138,7 +138,10 @@ export function ConversationRoot({
     ...(inert
       ? { disabled: true, placeholder: t('placeholder.workspace') }
       : blocked
-        ? { disabled: true, placeholder: composerBlock.reason }
+        // `blocked`, not `disabled`: the bar refuses input either way, but a
+        // block keeps the model seat live because choosing a model is how the
+        // user clears it.
+        ? { blocked: composerBlock, placeholder: composerBlock.reason }
         : hero ? { placeholder: t('placeholder.hero') } : {}),
     overlay: renderSlot('conversation.input.overlay', {}),
     leftItems: zone === undefined ? null : renderSlot('conversation.input.left', zone),

packages/client/ui-conversation/src/client/skeleton/InputBar.tsx

@@ -37,7 +37,8 @@ export type InputBarProps = ComposerBarProps
 export function InputBar({
   useSession, useInput, inputActions, keyboard, resolveSubmitMode, toggleCommandMenu, stop, command, t,
   renderSlot, useNotices, useLexicon, useMenuLauncher,
-  useProjection, sessionId, variant, disabled: inert = false, placeholder, accessory, overlay, leftItems, rightItems, footer,
+  useProjection, sessionId, variant, disabled: inert = false, blocked, placeholder,
+  accessory, overlay, leftItems, rightItems, footer,
 }: InputBarProps) {
   const input = useInput(s => s)
   const notice = useNotices(s => s)
@@ -86,8 +87,13 @@ export function InputBar({
   // inert no-workspace state, or the machine faces absent (no session). The
   // transient machine locks (adjudicating pending / submitting) render
   // read-only — the draft stays visible and focused, keystrokes drop.
-  const disabled = removed || inert || !live
+  const disabled = removed || inert || !live || blocked !== undefined
   const locked = disabled
+  // The model seat is the ONE control a block leaves live: every block this
+  // contract has is cleared by choosing a model, so locking it too would leave
+  // the composer asking for the only thing it prevents. The other reasons to
+  // be disabled do lock it — there is no session to choose a model for.
+  const modelSeatLocked = removed || inert || !live
   const machineBusy = input?.phase === 'adjudicating' || input?.phase === 'submitting'
 
   // Scroll the draft scrollport the minimum that brings `caret` into view — the
@@ -512,7 +518,7 @@ export function InputBar({
           </div>
           <div className={css.trailing}>
             {rightItems}
-            {renderSlot('conversation.input.model', { locked })}
+            {renderSlot('conversation.input.model', { locked: modelSeatLocked })}
             <ContextMeter useProjection={useProjection} t={t} />
             {/* {machineBusy && <span className={css.pending} data-input-pending aria-label="处理中" />} */}
             <Tooltip label={primaryLabel} side="top" delayMs={500}>