I started the mission with badly damaged Spark (it had 1 hp without armor bonus hp), healed myself with Repair ability to around 9 hp, finished the mission (even got the steam achievement), and Spark returned fully healed to the barracks.
Conditions:
- Spark had 1/12 hp in the barracks
- Equipped Reinforced Frame & Plated Bit
- Healed once in the mission (for 7 hp), took no damage at all
- It was a quick response mission (supply convoy)