diff --git a/frontend/src/lib/consultation-run-timeline.ts b/frontend/src/lib/consultation-run-timeline.ts
index 827f1ad2..7798ea35 100644
--- a/frontend/src/lib/consultation-run-timeline.ts
+++ b/frontend/src/lib/consultation-run-timeline.ts
@@ -144,7 +144,7 @@ export function consultationTimelineFromSettled(input: {
   thinkingText?: string;
   thinkingSections?: readonly PublicThinkingSection[];
   agentExecutionReceipt?: AgentExecutionReceipt;
-}): ConsultationTimelineRow[] {
+}): readonly ConsultationTimelineRow[] {
   const text = input.text?.trim() ?? "";
   const sections = input.thinkingSections ?? [];
   const receipt = input.agentExecutionReceipt;