Public-readiness: remove internal Slack references from public-facing files #273

Pre-public blocker. Internal Slack URL https://gsa.enterprise.slack.com/archives/C0B44531QLE + "agentic-coding Slack channel" pointers in public-facing files (7 places).

Locations (verified)

• .github/ISSUE_TEMPLATE/config.yml:4 (URL + channel ID)
• README.md:611
• CONTRIBUTING.md:15, :19, :384
• SECURITY.md:23
• .github/ISSUE_TEMPLATE/question.yml:13
• docs/QUICKSTART_SBX.md:583 ("#agentic-coding (GSA internal)")

Fix

Replace with GitHub Issues/Discussions. Add a CI grep-guard against gsa.enterprise.slack.com.

Part of the public-readiness epic. AI-assisted (OpenCode); requires human review.