[PIR][WP10] Reversible-action verification stage (WorldCycle pattern, arXiv:2608.04964)

Epic: #837 · Plan: docs/research/perpetual-intelligence-runtime/03-program-plan.md

Goal

Add reversible-action-sequence verification between "observe consequences" and the promotion-gate evaluation in the physical loop.

The mechanism: an action sequence composed with its inverse should return the world to the initial state. Divergence from that closed cycle is an annotation-free supervision signal — no human labels required. This is how the program satisfies invariant 6 ("every physical action produces new evidence") with evidence that is self-verifying rather than self-reported.

Evidence

arXiv:2608.04964 — "WorldCycle: Self-Verifiable Reinforcement Learning for Long-Horizon Video World Models," submitted 2026-08-05. Grade A, exact numeric match. The abstract states verbatim: "WorldCycle reduces state returning drift by up to 44% and lifts composite-action accuracy nearly 4x over the base model." A diagnostic benchmark, CycleBench, ships alongside it. No name collision.

Acceptance criteria

• A CycleBench-equivalent internal benchmark shows the target improvement over a no-WorldCycle baseline — up to 44% long-horizon drift reduction and ~4x composite-action accuracy as the internal acceptance bar. Report our own measured numbers; never restate the paper's figures as if they were ours.
• A reversible-action-cycle verifier runs on every physical action sequence before its results reach the promotion gate.
• Cycle-closure error is computed and recorded per action sequence, and is available as an input signal to the promotion verdict.
• Verification results are witness-logged so the acceptance test can attribute drift reduction to this stage specifically.
• Sequences whose inverse is not well-defined are handled explicitly — either excluded with a recorded reason, or verified by a documented alternative. Never silently passed.
• Proposed crate: ruvector-worldcycle-verify under crates/.

Dependencies

WP9 (#841) — this stage sits inside that loop. Feeds WP2's gate as an evaluation input. Blocks WP12 (#843).

Start by reading docs/research/perpetual-intelligence-runtime/03-program-plan.md and dependency issue #841 to understand where this stage fits in the physical loop. Implement the proposed crates/ruvector-worldcycle-verify stage and define how cycle-closure errors, witness logs, and non-invertible sequences reach the promotion gate; done requires an internal CycleBench-equivalent benchmark with reported measured results.