diff --git a/packages/app/e2e/regression/timeline-stream.spec.ts b/packages/app/e2e/regression/timeline-stream.spec.ts
index b8cb9cd48ad..808abaae6b6 100644
--- a/packages/app/e2e/regression/timeline-stream.spec.ts
+++ b/packages/app/e2e/regression/timeline-stream.spec.ts
@@ -650,6 +650,43 @@ test.describe("Working", () => {
     })
   }
 
+  test("keeps Working while a new read joins a standalone read group", async ({ page }) => {
+    const timeline = await setupTimeline(page, {
+      messages: [
+        userMessage(),
+        assistantMessage(
+          ["one", "two", "three"].map((name) =>
+            toolPart(`prt_read_${name}`, "read", "completed", { path: `src/${name}.ts` }),
+          ),
+          { completed: false },
+        ),
+      ],
+      settings: { timelineDetail: timelinePresets[0].value },
+    })
+
+    const working = page.locator('[data-component="session-working"]')
+    const group = page.locator('[data-component="read-tool-group"]')
+    const shimmer = group.locator('[data-component="text-shimmer"]')
+    await expect(group).toHaveAttribute("data-timeline-part-ids", "prt_read_one,prt_read_two,prt_read_three")
+    await expect(working).toBeVisible()
+
+    await timeline.send(partUpdated(toolPart("prt_read_four", "read", "streaming", { path: "src/four.ts" })))
+    await expect(group).toHaveAttribute(
+      "data-timeline-part-ids",
+      "prt_read_one,prt_read_two,prt_read_three,prt_read_four",
+    )
+    await expect(shimmer).toHaveAttribute("data-active", "true")
+    await expect(working).toBeVisible()
+
+    await timeline.send(partUpdated(toolPart("prt_read_four", "read", "running", { path: "src/four.ts" })))
+    await expect(group.locator('[data-slot="basic-tool-tool-subtitle"]')).toHaveText("one.ts, two.ts, three.ts, four.ts")
+    await expect(working).toBeVisible()
+
+    await timeline.send(partUpdated(toolPart("prt_read_four", "read", "completed", { path: "src/four.ts" })))
+    await expect(shimmer).toHaveAttribute("data-active", "false")
+    await expect(working).toBeVisible()
+  })
+
   for (const grouped of [false, true]) {
     test(`uses ${grouped ? "grouped" : "standalone"} background shell presentation`, async ({ page }) => {
       await setupTimeline(page, {
diff --git a/packages/app/src/session/timeline/message-timeline.tsx b/packages/app/src/session/timeline/message-timeline.tsx
index 74405425998..f19bbcf70b8 100644
--- a/packages/app/src/session/timeline/message-timeline.tsx
+++ b/packages/app/src/session/timeline/message-timeline.tsx
@@ -374,8 +374,9 @@ function MessageTimelineView(
         return message?.type === "compaction" && message.status === "running"
       }
 
-      // Used groups keep the fallback regardless of disclosure state.
-      if (!Predicate.isTagged(row, "AssistantPart") || row.group.type === "context") return false
+      // Used and read groups keep the fallback, so each new read does not swap Working out for its short call.
+      if (!Predicate.isTagged(row, "AssistantPart") || row.group.type === "context" || row.group.type === "read")
+        return false
 
       return (row.group.type === "part" ? [row.group.ref] : row.group.refs).some((ref) => {
         const content = Timeline.resolveContent(messageByID().get(ref.messageID), ref.partID)