diff --git a/apps/web/src/session-logic.test.ts b/apps/web/src/session-logic.test.ts
index 0b846e8c035d..846ab88d9e85 100644
--- a/apps/web/src/session-logic.test.ts
+++ b/apps/web/src/session-logic.test.ts
@@ -2626,7 +2626,7 @@ describe("session activity performance", () => {
     expect(appendedEntries[1]).toBe(initialEntries[1]);
   });
 
-  it("updates 20,000 ordered tool activities within 100 ms", () => {
+  it("updates 20,000 ordered tool activities within 250 ms", () => {
     const activities = Array.from({ length: 20_000 }, (_, index) =>
       makeActivity({
         id: `benchmark-tool-${index}`,
@@ -2663,6 +2663,8 @@ describe("session activity performance", () => {
 
     const startedAt = performance.now();
     expect(deriveWorkLogEntries(updatedActivities)).toHaveLength(20_001);
-    expect(performance.now() - startedAt).toBeLessThan(100);
+    // GitHub-hosted CI has seen the 100ms #8006 budget fail at ~139ms on the
+    // same tree that passed PR CI. 250ms still fails a quadratic rebuild.
+    expect(performance.now() - startedAt).toBeLessThan(250);
   });
 });
diff --git a/apps/web/src/session-logic.ts b/apps/web/src/session-logic.ts
index d4a35c3f6c28..cc6a3bf76fdf 100644
--- a/apps/web/src/session-logic.ts
+++ b/apps/web/src/session-logic.ts
@@ -1029,10 +1029,22 @@ function isAgentInternalActivity(activity: OrchestrationThreadActivity): boolean
   return typeof payload.agentId === "string" && payload.agentId.trim().length > 0;
 }
 
+/** Streaming appends are already ordered; skip the n log n copy+sort on that path. */
+function orderActivities(
+  activities: ReadonlyArray<OrchestrationThreadActivity>,
+): ReadonlyArray<OrchestrationThreadActivity> {
+  for (let index = 1; index < activities.length; index++) {
+    if (compareActivitiesByOrder(activities[index - 1]!, activities[index]!) > 0) {
+      return activities.toSorted(compareActivitiesByOrder);
+    }
+  }
+  return activities;
+}
+
 export function deriveWorkLogEntries(
   activities: ReadonlyArray<OrchestrationThreadActivity>,
 ): WorkLogEntry[] {
-  const ordered = [...activities].toSorted(compareActivitiesByOrder);
+  const ordered = orderActivities(activities);
   const entries: DerivedWorkLogEntry[] = [];
   // Answers arrive in a separate activity from the questions; fold them back
   // into the entry that asked, so one round trip renders as one Q&A card.