diff --git a/src/relay/pty-handler-output-drain-differential.test.ts b/src/relay/pty-handler-output-drain-differential.test.ts
index 22ba265cd10..cbaee4bcb75 100644
--- a/src/relay/pty-handler-output-drain-differential.test.ts
+++ b/src/relay/pty-handler-output-drain-differential.test.ts
@@ -159,16 +159,20 @@ describe('relay PTY output drain — differential vs the pre-optimization snapsh
   async function spawnPtys(count: number): Promise<string[]> {
     const ids: string[] = []
     for (let i = 0; i < count; i++) {
+      let dataCallback!: (data: string) => void
+      let exitCallback!: (event: { exitCode: number }) => void
       mockPtySpawn.mockReturnValueOnce({
         ...mockPtyInstance,
         onData: vi.fn((cb: (data: string) => void) => {
-          dataCallbacks.set(`pty-${i + 1}`, cb)
+          dataCallback = cb
         }),
         onExit: vi.fn((cb: (event: { exitCode: number }) => void) => {
-          exitCallbacks.set(`pty-${i + 1}`, cb)
+          exitCallback = cb
         })
       })
       const spawned = (await dispatcher.callRequest('pty.spawn', {})) as { id: string }
+      dataCallbacks.set(spawned.id, dataCallback)
+      exitCallbacks.set(spawned.id, exitCallback)
       ids.push(spawned.id)
     }
     return ids
diff --git a/src/relay/subprocess.test.ts b/src/relay/subprocess.test.ts
index 18d837bb4ef..1aea75a800d 100644
--- a/src/relay/subprocess.test.ts
+++ b/src/relay/subprocess.test.ts
@@ -204,7 +204,7 @@ describe('Subprocess: Relay entry point', () => {
     const repairedId = relay.send('pty.spawn', { cols: 80, rows: 24 })
     const repaired = await relay.waitForResponse(repairedId)
     expect(repaired.error).toBeUndefined()
-    expect(repaired.result).toMatchObject({ id: 'pty-1' })
+    expect(repaired.result).toMatchObject({ id: expect.any(String) })
   }, 10_000)
 
   it('reloads node-pty after a late native binding failure without restarting', async () => {
@@ -228,7 +228,7 @@ describe('Subprocess: Relay entry point', () => {
     const repairedId = relay.send('pty.spawn', { cols: 80, rows: 24 })
     const repaired = await relay.waitForResponse(repairedId)
     expect(repaired.error).toBeUndefined()
-    expect(repaired.result).toMatchObject({ id: 'pty-2' })
+    expect(repaired.result).toMatchObject({ id: expect.any(String) })
   }, 10_000)
 
   it('responds to fs.stat over stdin/stdout', async () => {