diff --git a/src/gateway/server.sessions.gateway-server-sessions-a.e2e.test.ts b/src/gateway/server.sessions.gateway-server-sessions-a.e2e.test.ts
index 4e5a4c8216..9ad195d25d 100644
--- a/src/gateway/server.sessions.gateway-server-sessions-a.e2e.test.ts
+++ b/src/gateway/server.sessions.gateway-server-sessions-a.e2e.test.ts
@@ -4,6 +4,7 @@ import path from "node:path";
 import { afterAll, beforeAll, beforeEach, describe, expect, test, vi } from "vitest";
 import { DEFAULT_PROVIDER } from "../agents/defaults.js";
 import { startGatewayServerHarness, type GatewayServerHarness } from "./server.e2e-ws-harness.js";
+import { createToolSummaryPreviewTranscriptLines } from "./session-preview.test-helpers.js";
 import {
   connectOk,
   embeddedRunMock,
@@ -437,15 +438,7 @@ describe("gateway server sessions", () => {
     testState.sessionStorePath = storePath;
     const sessionId = "sess-preview";
     const transcriptPath = path.join(dir, `${sessionId}.jsonl`);
-    const lines = [
-      JSON.stringify({ type: "session", version: 1, id: sessionId }),
-      JSON.stringify({ message: { role: "user", content: "Hello" } }),
-      JSON.stringify({ message: { role: "assistant", content: "Hi" } }),
-      JSON.stringify({
-        message: { role: "assistant", content: [{ type: "toolcall", name: "weather" }] },
-      }),
-      JSON.stringify({ message: { role: "assistant", content: "Forecast ready" } }),
-    ];
+    const lines = createToolSummaryPreviewTranscriptLines(sessionId);
     await fs.writeFile(transcriptPath, lines.join("\n"), "utf-8");
 
     await writeSessionStore({
diff --git a/src/gateway/session-preview.test-helpers.ts b/src/gateway/session-preview.test-helpers.ts
new file mode 100644
index 0000000000..a7461c54f5
--- /dev/null
+++ b/src/gateway/session-preview.test-helpers.ts
@@ -0,0 +1,11 @@
+export function createToolSummaryPreviewTranscriptLines(sessionId: string): string[] {
+  return [
+    JSON.stringify({ type: "session", version: 1, id: sessionId }),
+    JSON.stringify({ message: { role: "user", content: "Hello" } }),
+    JSON.stringify({ message: { role: "assistant", content: "Hi" } }),
+    JSON.stringify({
+      message: { role: "assistant", content: [{ type: "toolcall", name: "weather" }] },
+    }),
+    JSON.stringify({ message: { role: "assistant", content: "Forecast ready" } }),
+  ];
+}
diff --git a/src/gateway/session-utils.fs.test.ts b/src/gateway/session-utils.fs.test.ts
index 80be91452f..f827f051f5 100644
--- a/src/gateway/session-utils.fs.test.ts
+++ b/src/gateway/session-utils.fs.test.ts
@@ -2,6 +2,7 @@ import fs from "node:fs";
 import os from "node:os";
 import path from "node:path";
 import { afterAll, afterEach, beforeAll, describe, expect, test, vi } from "vitest";
+import { createToolSummaryPreviewTranscriptLines } from "./session-preview.test-helpers.js";
 import {
   archiveSessionTranscripts,
   readFirstUserMessageFromTranscript,
@@ -558,15 +559,7 @@ describe("readSessionPreviewItemsFromTranscript", () => {
 
   test("returns recent preview items with tool summary", () => {
     const sessionId = "preview-session";
-    const lines = [
-      JSON.stringify({ type: "session", version: 1, id: sessionId }),
-      JSON.stringify({ message: { role: "user", content: "Hello" } }),
-      JSON.stringify({ message: { role: "assistant", content: "Hi" } }),
-      JSON.stringify({
-        message: { role: "assistant", content: [{ type: "toolcall", name: "weather" }] },
-      }),
-      JSON.stringify({ message: { role: "assistant", content: "Forecast ready" } }),
-    ];
+    const lines = createToolSummaryPreviewTranscriptLines(sessionId);
     writeTranscriptLines(sessionId, lines);
     const result = readPreview(sessionId);