Physical-Evidence Progress Gate

Problem

The physical world returns no status code. A grasp that closed on the object and one that closed a centimetre short produce the same emitted command and the same absence of an error, so treating an attempted action as completed progress is the cheapest available rule and the one most systems fall into. That rule converts a recoverable local slip into a persistent belief that the subgoal is done. Every subsequent step is then planned against a world state that does not exist, and the error compounds instead of being corrected at the point where it was still one missed grasp.

Solution

Treat the progress pointer as a write that has to be earned. After the policy acts, a cheap signal from the body — gripper closure, contact force, a joint-torque spike — decides whether an interaction plausibly occurred and therefore whether a verification look is worth its cost. When it fires, the agent re-observes the scene and compares the new observation against the state before the action, tying the observed change to the language of the subgoal: point tracking establishes that the named object moved, a cross-view comparison establishes that it ended where the subgoal said it should. Only a positive verdict advances the pointer and writes the subgoal as achieved. A negative verdict, or evidence too partial to judge, leaves the pointer where it is and hands the verdict to retry, replanning or escalation. The default on silence is to hold, not to advance, so the gate degrades toward stalling rather than toward a confidently wrong world model.

When to use

• An action's success cannot be read back from any authoritative record and has to be re-observed through sensors.
• The task is represented as a sequence of subgoals with a pointer or memory that later steps plan against.
• The acting policy is frozen or otherwise cannot be changed to report its own execution failures.
• Ordinary slips such as a missed grasp or a dropped object are frequent enough that compounding them is the dominant failure mode.