Fault detection & recovery

AETHER runs DRL-first hybrid FDIR: a PPO network consumes a 15-dimensional sensor observation vector and classifies faults in real time, with recovery logic that returns the robot to a safe state. It runs concurrently with motion in realworld mode and the sim loop.

• Fault injection for testing: --faults {disabled,enabled,heavy} and sim scenarios imu_fault, battery, compound, fault_heavy.
• Learning: PPO weights update online by default; freeze with --no-learning for controlled benchmarking.