feat(blog/river-is-the-prompt): add §O — double-entry bookkeeping of AI + role-continuity in §M D6
This is a live, recomputable drift receipt — the on-chip proof of where this commit's work landed (in its authorized domain, out of it, or unplaced), sealed with a signature anyone can verify. It is the same receipt shipped in the on-commit email, hosted here so the claim is checkable on the open web. The full receipt (attestation, density panel, full commit message) publishes at /commit/c734dc4e5/ shortly after the commit lands.

Sufficient for: where it landed, re-runnable from the commit: same bytes, same hash.
NOT sufficient for: whether the work was good, which is undecidable (Rice, 1953); nothing here claims it. Rice (1953): no program can decide, in general, whether another program is correct.