diff --git a/src/gateway/server-startup-session-migration.test.ts b/src/gateway/server-startup-session-migration.test.ts
index 8e08be146141..ad40ed8caf7c 100644
--- a/src/gateway/server-startup-session-migration.test.ts
+++ b/src/gateway/server-startup-session-migration.test.ts
@@ -14,6 +14,14 @@ function makeCfg() {
   >[0]["cfg"];
 }
 
+function firstLogMessage(log: ReturnType<typeof vi.fn>, label: string): string {
+  const [message] = log.mock.calls[0] ?? [];
+  if (typeof message !== "string") {
+    throw new Error(`expected ${label} message`);
+  }
+  return message;
+}
+
 describe("runStartupSessionMigration", () => {
   it("logs changes when orphaned keys are canonicalized", async () => {
     const log = makeLog();
@@ -28,7 +36,9 @@ describe("runStartupSessionMigration", () => {
     });
     expect(migrate).toHaveBeenCalledOnce();
     expect(log.info).toHaveBeenCalledOnce();
-    expect(log.info.mock.calls.at(0)?.[0]).toContain("canonicalized orphaned session keys");
+    expect(firstLogMessage(log.info, "startup migration info")).toContain(
+      "canonicalized orphaned session keys",
+    );
     expect(log.warn).not.toHaveBeenCalled();
   });
 
@@ -45,7 +55,9 @@ describe("runStartupSessionMigration", () => {
     });
     expect(log.info).not.toHaveBeenCalled();
     expect(log.warn).toHaveBeenCalledOnce();
-    expect(log.warn.mock.calls.at(0)?.[0]).toContain("session key migration warnings");
+    expect(firstLogMessage(log.warn, "startup migration warning")).toContain(
+      "session key migration warnings",
+    );
   });
 
   it("silently continues when no changes needed", async () => {
@@ -69,7 +81,8 @@ describe("runStartupSessionMigration", () => {
       deps: { migrateOrphanedSessionKeys: migrate },
     });
     expect(log.warn).toHaveBeenCalledOnce();
-    expect(log.warn.mock.calls.at(0)?.[0]).toContain("migration failed during startup");
-    expect(log.warn.mock.calls.at(0)?.[0]).toContain("disk full");
+    const warning = firstLogMessage(log.warn, "startup migration failure warning");
+    expect(warning).toContain("migration failed during startup");
+    expect(warning).toContain("disk full");
   });
 });