fix(web): keep the plan card to decisions it can actually answer

Review follow-ups on the presentation intent.

The card claimed any single-question request declaring the intent, then sent one
of two labels — so a producer offering a third option, or a multi-select batch,
lost answers the generic flow would have shown. That contradicts the intent's
own contract, so `planReviewOf` now claims only a binary single choice and
leaves everything else to the flow that can express it.

`ask()` also rejects a plan-review intent on a question with no `detail`: the
intent declares detail IS the plan, and without one a honouring UI asks the
user to approve something invisible. The client keeps its own fallback — it sits
downstream of a wire boundary — but the misconfiguration now fails at the asker.

`planReviewOf` stops being a value export of the client contract face (client
export discipline: pure helpers stay internal; the tests already import it
relatively), and the ui-question README fallback list, both languages, now
states every condition the code enforces.

packages/ui/user-interaction/src/index.ts

@@ -87,10 +87,13 @@ export class UserInteractionService extends Service {
     if (request.questions.length === 0) {
       throw new UserInteractionError('ask_user_question requires at least one question', 'EMPTY_QUESTIONS')
     }
-    // A presentation intent names an option label the types cannot pin to its
-    // own question's option list. A UI honouring the intent answers with that
-    // label, so a name matching nothing would answer a choice the asker never
-    // offered — caught here, at the asker, rather than in a UI.
+    // A presentation intent asserts two things the types cannot: that the
+    // named approve label is one of this question's own options, and that a
+    // plan-review carries the plan it is a review of. A UI honouring the
+    // intent answers with that label, and shows that detail as the plan, so
+    // either gap would put a choice the asker never offered — or an approval of
+    // something invisible — in front of the user. Caught at the asker, where
+    // the mistake is, rather than in each UI.
     for (const question of request.questions) {
       const intent = question.intent
       if (intent === undefined) continue
@@ -100,6 +103,11 @@ export class UserInteractionService extends Service {
           + `${JSON.stringify(intent.approve)} names none of its options`,
           'BAD_INTENT')
       }
+      if (question.detail === undefined) {
+        throw new UserInteractionError(
+          `question ${question.id} declares intent ${intent.kind} without the detail it reviews`,
+          'BAD_INTENT')
+      }
     }
     if (this.provider === undefined) {
       throw new UserInteractionError('no user-interaction provider is registered', 'NO_PROVIDER')

packages/ui/user-interaction/src/types.ts

@@ -21,7 +21,7 @@ export interface AskUserQuestionOption {
  * either way — an intent shapes presentation only, never the protocol.
  */
 export type AskUserQuestionIntent = {
-  /** A plan submitted for review: `detail` is the plan markdown, and the decision approves or declines it. */
+  /** A plan submitted for review: `detail` is the plan markdown `ask()` requires, and the decision approves or declines it. */
   kind: 'plan-review'
   /**
    * The option label that approves the plan; every other option declines it.