Robot policy failures are often semantically coherent rather than noisy: a robot that fails to open a drawer will open the adjacent oven and place cutlery there. The error is a constraint-satisfaction failure, not a perception or control breakdown, which means failure modes can be classified by whether the model's intent was world-consistent.
If failures produce plausible-but-wrong actions, then standard anomaly/threshold monitoring will not catch them, because the output distribution looks in-distribution. Evaluation must test constraint adherence (task-specific rules), not just plausibility or success rate.
Applies to any learned agent: separate 'incoherent failure' (model didn't understand) from 'coherent but non-compliant failure' (model understood but violated a constraint). These require different mitigations — better representations vs. explicit constraint/guardrail layers.
Even mistakes made by LLM-backed robots often make semantic sense rather than random noise.
A robot trying to put cutlery in a drawer, failing, and instead opening the adjacent oven to store them.