ask_user upgrades: rich options, grouped questions, option previews (OPE-51)

Options accept {label, description, recommended, preview} objects (plain
strings unchanged — old sessions render as today's pills), and `questions`
groups up to 4 questions into one call, rendered as a stepper via the
header chips. Any option preview switches the card to a two-pane layout:
options left, monospace pane right, following hover/focus.

Grouped calls resolve with a JSON map keyed by header-or-question and
return {answers: {...}} to the agent (single stays {answer: ...});
a grouped item's first question doubles as its title/options so channel
mirrors and legacy surfaces degrade sensibly. Channel buttons use option
labels; grouped items mirror as text with the open-the-app hint.

coworker/engine.py

@@ -826,6 +826,13 @@ class TurnEngine:
         from the Inbox when unattended), and return it as the tool result."""
         args = tool_call.arguments or {}
         question = str(args.get("question", "")).strip()
+        # Grouped form (OPE-51): `questions` alone is a valid call — the singular field may be
+        # empty. The asker normalizes/validates the entries; here only "is anything asked?".
+        if not question:
+            for entry in args.get("questions") or []:
+                if isinstance(entry, dict) and str(entry.get("question", "")).strip():
+                    question = str(entry["question"]).strip()
+                    break
         if self.question_asker is None or not question:
             result: dict[str, Any] = {
                 "answer": "",
@@ -847,7 +854,7 @@ class TurnEngine:
                 "error": "no response",
             }
 
-        status = "ok" if result.get("answer") else "denied"
+        status = "ok" if (result.get("answer") or result.get("answers")) else "denied"
         self.messages.append(_tool_result_message(tool_call, result))
         self._audit(
             tool_call,