Create the coordination artifact
Before the first implementation PR, add docs/features/<epic-slug>/CHANGELOG.md with status, epic link, related context, current state, and newest-first changes. Every PR in the epic updates it.
Record observed state
Delivered describes behavior already safe to depend on. In transition names temporary compatibility or migration state. Next and Blockers describe what is actually unblocked or constrained. Link tickets and PRs rather than copying full requirements.
Preserve authoritative boundaries
Feature and architecture docs own current behavior. ADRs own consequential rationale. The issue tracker owns acceptance criteria, ownership, and backlog state. A changelog cannot substitute for updates to those sources when a contract changes.
Close cleanly
Mark the epic completed, move durable facts into authoritative docs, resolve remaining work in the issue tracker, and retain the changelog only when its migration or compatibility history remains useful.