[quality] Research User Group page sends readers to a Slack sign-in wall instead of the CNCF Slack invite #2000

Finding

docs/community/user-groups/research/index.md ends its How to participate list with:

- Join
  [`#ug-research` on CNCF Slack](https://cloud-native.slack.com/archives/CTW1NRLBW).

That target is a workspace-internal deep link. Verified with curl:

https://cloud-native.slack.com/archives/CTW1NRLBW
  -> 302 https://cloud-native.slack.com/?redir=%2Farchives%2FCTW1NRLBW%3Fname%3DCTW1NRLBW
  -> 403

Deterministic across three consecutive requests. A reader who is already signed in to the CNCF Slack workspace lands in the channel; a reader who is not — precisely the audience a "How to participate" list is written for — gets a workspace sign-in wall and no route to join.

The three sibling pages do not have this problem. public-sector, telecom and platform-engineering all name the channel in text and link the open invite page:

- Join `#tug` on [CNCF Slack](https://slack.cncf.io/)

The Research page was added in #1996 (93c38f7, 2026-10-29) and is the only page under docs/community/user-groups/ that links a slack.com workspace URL.

Secondary effect. npm run check:links reports this URL as 1 dead link found. The weekly check-links workflow last ran green on 2026-10-26 (run 40270211879), three days before the page merged, so the job goes red on main at its next scheduled run on a link no open pull request introduced.

Recommendation

• Link https://slack.cncf.io/ from the Research page and name #ug-research in text, matching the three sibling group pages.
• Guard the convention in tests/community-group-coverage.test.mjs — the file that already pins User Group page/report/sidebar agreement — so a future group page cannot reintroduce a workspace deep link.

Priority

• Impact: medium (a published participation link is unusable for the readers it targets, and it breaks a scheduled check on main)
• Effort: low

Remit

ADR 0008 rule 1: a defect an end user can observe on the production site (a broken navigation path), and a CI check failing on main for a reason unrelated to any open pull request.

Filed by quality agent (hold-gated mode)

🐝 Hive Agent: quality | Instance: hosted-available-lke648397-260827-5n31 | SHA: b4ea678

— hive: agent=quality backend=copilot model=claude-opus-5 copilot=1.0.88