fix: harden phase summary open questions

frontend/src/viewers/PhaseSummaryViewer.tsx

@@ -1,7 +1,14 @@
 import { Badge } from "../components/ui/badge";
 import { MarkdownView } from "./MarkdownView";
 import { statusBadgeClass } from "./statusBadge";
-import type { PhaseCheck, PhaseSection, PhaseSectionItem, PhaseSummaryV2, PhaseTable } from "./artifactV2";
+import {
+  phaseOpenQuestionText,
+  type PhaseCheck,
+  type PhaseSection,
+  type PhaseSectionItem,
+  type PhaseSummaryV2,
+  type PhaseTable,
+} from "./artifactV2";
 
 const CODE_CHIP = "rounded-md bg-muted px-1.5 py-0.5 font-mono text-xs text-foreground/90";
 
@@ -69,6 +76,12 @@ function TableRecap({ table }: { table: PhaseTable }) {
 }
 
 export function PhaseSummaryViewer({ phase }: { phase: PhaseSummaryV2 }) {
+  const openQuestions = Array.isArray(phase.open_questions)
+    ? (phase.open_questions as unknown[])
+        .map(phaseOpenQuestionText)
+        .filter((question): question is string => question !== null)
+    : [];
+
   return (
     <div className="flex flex-col gap-4">
       <h3 className="thot-label">
@@ -101,11 +114,11 @@ export function PhaseSummaryViewer({ phase }: { phase: PhaseSummaryV2 }) {
         </div>
       )}
 
-      {phase.open_questions && phase.open_questions.length > 0 && (
+      {openQuestions.length > 0 && (
         <div>
           <h4 className="thot-label mb-1">Open questions</h4>
           <ul className="list-disc space-y-1 pl-5 text-sm text-foreground/90 marker:text-muted-foreground">
-            {phase.open_questions.map((q, i) => (
+            {openQuestions.map((q, i) => (
               <li key={i}>{q}</li>
             ))}
           </ul>