release-beta: CHANGELOG-before-tag rule is documented, not enforced

Start in script/release-preflight.ts and compare how it already fails the tag stage for tag collisions, version sanity, prerelease ancestry, and marker guards. Add a CHANGELOG.md check for the version being tagged, matching a section like ## [X.Y.Z] or X.Y.Z-beta.N. Done means the preflight fails before tagging when that section is missing and passes when it exists.

What happened

v0.11.0-beta.5 was tagged and published without a CHANGELOG.md entry. Every prior beta (beta.1, beta.3, beta.4) had shipped with its own dedicated section; beta.5 didn't, because the release-beta skill's pre-tag gate checklist never asked for one. Nothing caught it before the tag existed — the changelog is baked into the compiled binary at build time (packages/opencode/script/build.ts reads CHANGELOG.md into OPENCODE_CHANGELOG), so by the time anyone noticed, the fix could only apply to the next beta, not the one already built and published.

What #1281 fixes

Adds the missing beta.5 entry, and adds an explicit gate + Hard Rule to .claude/commands/release-beta.md telling whoever runs the release to check for a CHANGELOG.md entry before tagging.

What's still open

That's a documentation fix, not an enforced one — it relies on whoever (human or agent) runs the release actually reading and following that step. script/release-preflight.ts already automates several other pre-tag checks (tag collision, version sanity vs npm, prerelease ancestry, marker guard) that used to be the same kind of "remember to check this" gate. This should be one more: have release-preflight.ts parse CHANGELOG.md and fail the tag stage if there's no ## [X.Y.Z] (or X.Y.Z-beta.N) section for the version being tagged, the same way it already fails on a tag collision.

That would make this a hard, automatic stop instead of a step someone can skip under release pressure — which is exactly how beta.5 shipped without one.

Related: #1281

🤖 Generated with Claude Code

https://claude.ai/code/session_01H8gZMvZunXzx4LPSZzCafq