fix(web): preserve handoffs before superseded attempt folds (#26333)

Author: Yash-Singh1

apps/web/src/components/chat/MessagesTimeline.logic.test.ts

@@ -2642,6 +2642,15 @@ describe("v2 run and attempt history", () => {
       completedAt: null,
     };
     const timelineEntries = [
+      {
+        id: "context-handoff-entry",
+        kind: "event" as const,
+        createdAt: "2026-01-01T00:00:00Z",
+        attempt: supersededAttempt,
+        projectedItem: {
+          item: { type: "handoff", runId },
+        } as never,
+      },
       {
         id: "initial-user-entry",
         kind: "message" as const,
@@ -2744,6 +2753,7 @@ describe("v2 run and attempt history", () => {
 
     const collapsedRows = deriveMessagesTimelineRows(common);
     expect(collapsedRows.map((row) => row.id)).toEqual([
+      "context-handoff-entry",
       "initial-user-entry",
       `attempt-fold:${supersededAttemptId}`,
       "superseded-thread-created-entry",
@@ -2762,6 +2772,7 @@ describe("v2 run and attempt history", () => {
       expandedAttemptIds: new Set([supersededAttemptId]),
     });
     expect(expandedRows.map((row) => row.id)).toEqual([
+      "context-handoff-entry",
       "initial-user-entry",
       `attempt-fold:${supersededAttemptId}`,
       "superseded-assistant-entry",

apps/web/src/components/chat/MessagesTimeline.logic.ts

@@ -770,6 +770,7 @@ function deriveSupersededAttemptFolds(
       completeAttemptIds.has(entry.attempt.id) ||
       unfoldedRunIds.has(entry.attempt.runId) ||
       (entry.kind === "message" && entry.message.role === "user") ||
+      (entry.kind === "event" && entry.projectedItem.item.type === "handoff") ||
       entry.kind === "html-render" ||
       entry.kind === "mcp-app" ||
       timelineEntryIsPersistentResourceCard(entry) ||