diff --git a/packages/client-runtime/src/state/threads-sync.test.ts b/packages/client-runtime/src/state/threads-sync.test.ts
index 131d277c5e6f..ae372ea938cd 100644
--- a/packages/client-runtime/src/state/threads-sync.test.ts
+++ b/packages/client-runtime/src/state/threads-sync.test.ts
@@ -1051,6 +1051,66 @@ describe("EnvironmentThreads", () => {
         expect((yield* SubscriptionRef.get(harness.threadState)).history.loading).toBe(false);
       }),
     );
+    const boundary = (fields: object, id = "boundary", ordinal = 2) => ({
+      ...command(id, "completed", 0, ordinal),
+      ...fields,
+    });
+    const message = (
+      inputIntent: "turn_start" | "steer",
+      createdBy: "agent" | "user",
+      id = "boundary",
+      ordinal = 2,
+    ) =>
+      boundary(
+        {
+          type: "user_message",
+          messageId: MessageId.make(id),
+          inputIntent,
+          createdBy,
+          creationSource: "mcp",
+          text: "Run every check",
+          attachments: [],
+        },
+        id,
+        ordinal,
+      );
+    it.effect.each([
+      ["an agent-started turn", message("turn_start", "agent"), ["3"]],
+      [
+        "a notification",
+        boundary({
+          type: "notification",
+          source: { kind: "delegated_task", taskIds: [] },
+          outcome: "completed",
+          summary: "Checks finished",
+        }),
+        ["3"],
+      ],
+      ["a steer, paging on to its turn", message("steer", "user"), ["3", "2", "1"]],
+    ] as const)("stops paging earlier history at %s", ([, item, expected]) =>
+      Effect.gen(function* () {
+        const pages: Record<string, ReadonlyArray<unknown>> = {
+          "3": [item],
+          "2": [command("work-1", "completed", 0, 1)],
+          "1": [message("turn_start", "user", "opener", 0)],
+        };
+        const requests: string[] = [];
+        const harness = yield* makeHarness({
+          cached: cachedItem(command("tail", "completed", 0, 3)),
+          cachedHistory: { historyCursor: "3", hasMoreHistory: true },
+          historyHttpClient: HttpClient.make((request, url) => {
+            const cursor = url.searchParams.get("cursor")!;
+            requests.push(cursor);
+            const items = (pages[cursor] ?? []) as ReadonlyArray<OrchestrationV2TurnItem>;
+            return Effect.succeed(
+              historyPage(request, items.map(localRow), String(Number(cursor) - 1)),
+            );
+          }),
+        });
+        expect(yield* harness.loadEarlier()).toEqual({ _tag: "loaded" });
+        expect(requests).toEqual(expected);
+      }),
+    );
     it.effect("loads deferred work on demand and resumes a failed page", () =>
       Effect.gen(function* () {
         const anchor = {
diff --git a/packages/client-runtime/src/state/threads.ts b/packages/client-runtime/src/state/threads.ts
index 3e8f3709a915..b67245e735cc 100644
--- a/packages/client-runtime/src/state/threads.ts
+++ b/packages/client-runtime/src/state/threads.ts
@@ -75,6 +75,17 @@ function formatHistoryError(error: unknown): string {
   return "Could not load earlier activity.";
 }
 
+// Steers join a running turn; every other user message opens one. The timeline shows every
+// notification as a response boundary, whether it opened its run or arrived mid-run.
+function startsTurn(item: OrchestrationV2TurnItem): boolean {
+  return (
+    item.type === "notification" ||
+    (item.type === "user_message" &&
+      item.inputIntent !== "steer" &&
+      item.inputIntent !== "promoted_queued_to_steer")
+  );
+}
+
 function historyMetaFromCachedSnapshot(
   snapshot: OrchestrationV2ThreadDetailSnapshot,
 ): ThreadHistoryMeta {
@@ -777,9 +788,7 @@ export const makeEnvironmentThreadState = Effect.fn("EnvironmentThreadState.make
               ? page.nextCursor !== null
               : throughEntryId === undefined &&
                 page.hasMoreHistory &&
-                !page.items.some(
-                  ({ item }) => item.type === "user_message" && item.createdBy === "user",
-                ));
+                !page.items.some(({ item }) => startsTurn(item)));
           if (keepPaging && (page.nextCursor === null || page.nextCursor === requestCursor))
             return yield* failLoad(
               workAnchorId === undefined