If governance must precede state mutation, publishing must proceed from a source of truth. Nothing becomes canonical until it passes a deterministic editorial gate — and the place it passes through is a substrate, not a folder of drafts.
The failure mode that lets an agent mutate state without authority also lets content reach an audience without vetting: a draft becomes a post because someone hit publish. Governed publishing needs what governed execution needs — a substrate that holds canon, and a gate between intent and canon. Drafts are proposals; canonical is admitted state.
Treating content as a substrate means the editorial gate is deterministic, not a matter of taste: a promote step that checks voice, grounding, and claim integrity, and refuses what fails. Once promoted, the canonical is immutable, and downstream surfaces consume it read-only. The pattern that governs a merge governs a sentence — nothing becomes canon without passing the gate.