original_read = StarletteUploadFile.read

    async def patched_read(self: StarletteUploadFile, size: int = -1) -> bytes:
        # Make the FIRST file slower *deterministically*
        if self.filename == "slow.txt":
            await anyio.sleep(0.05)
        return await original_read(self, size)

    monkeypatch.setattr(StarletteUploadFile, "read", patched_read)

    client = TestClient(app)

    files = [