A 52-year-old female with a history of ankylosing spondylitis and anterior cervical fusion (C5–C6) presents for emergency laparotomy for perforated peptic ulcer. Preoperative assessment shows severe cervical rigidity, inability to extend the neck, and a Mallampati score of III. Rapid sequence intubation is contraindicated due to the high risk of cervical spine instability. Awake fiberoptic intubation is planned. Which of the following is the MOST important prerequisite before attempting scope insertion?