diff --git a/tools/trap-sandbox/test-integration/duplicate.test.ts b/tools/trap-sandbox/test-integration/duplicate.test.ts
index fcc17c6..5a22667 100644
--- a/tools/trap-sandbox/test-integration/duplicate.test.ts
+++ b/tools/trap-sandbox/test-integration/duplicate.test.ts
@@ -10,22 +10,28 @@ test("duplicate traposId is resolved newest-wins", async () => {
   const sandbox = await startSandbox();
   const TRAPOS_ID = "9:dup";
 
+  // Newest-wins is decided by the order hello frames reach the gateway, which is
+  // independent of the client-side READY print order. Spawn the two computers
+  // sequentially — only start `second` once `first` is registered server-side —
+  // so `second` is unambiguously the newer registration.
   const first = startCraftos("gateway-client.lua", {
     computerId: 9,
     computerLabel: "dup",
     shellArgs: [sandbox.baseUrl, "-", "idle", "60"],
   });
-  const second = startCraftos("gateway-client.lua", {
-    computerId: 9,
-    computerLabel: "dup",
-    shellArgs: [sandbox.baseUrl, "-", "idle"],
-  });
 
+  let second: ReturnType<typeof startCraftos> | undefined;
   try {
     await waitFor(() => first.snapshot().includes("__SANDBOX_READY__"), 12_000, "first connected");
-    assert.ok(sandbox.registry.has("local", TRAPOS_ID), "first should be registered");
+    await waitFor(() => sandbox.registry.has("local", TRAPOS_ID), 2_000, "first registered server-side");
 
-    await waitFor(() => second.snapshot().includes("__SANDBOX_READY__"), 12_000, "second connected");
+    const secondHandle = startCraftos("gateway-client.lua", {
+      computerId: 9,
+      computerLabel: "dup",
+      shellArgs: [sandbox.baseUrl, "-", "idle"],
+    });
+    second = secondHandle;
+    await waitFor(() => secondHandle.snapshot().includes("__SANDBOX_READY__"), 12_000, "second connected");
     // Newest-wins: still exactly one registration for the shared id.
     assert.equal(sandbox.registry.count(), 1, "exactly one registration after the duplicate");
     assert.ok(sandbox.registry.has("local", TRAPOS_ID));
@@ -38,14 +44,14 @@ test("duplicate traposId is resolved newest-wins", async () => {
     throw new Error(
       formatFailure(
         error instanceof Error ? error.message : String(error),
-        `first:\n${first.snapshot()}\nsecond:\n${second.snapshot()}`,
+        `first:\n${first.snapshot()}\nsecond:\n${second?.snapshot() ?? "(not started)"}`,
       ),
       { cause: error },
     );
   } finally {
     first.abort();
-    second.abort();
-    await Promise.all([first.done.catch(() => undefined), second.done.catch(() => undefined)]);
+    second?.abort();
+    await Promise.all([first.done.catch(() => undefined), second?.done.catch(() => undefined)]);
     await sandbox.close();
   }
 });