Triage unmilestoned issues into release buckets or backlog

[flyingrobots]

Why this matters

Post-release planning found 196 open issues without a release milestone. Some are true backlog, but the new release process needs explicit release buckets for work that belongs to versioned trains.

Evidence

gh issue list --state open --limit 500 grouped by milestone after v18.1.2 showed:

• (none): 196 open issues
• v19.0.0: 13 open issues after v19 activation
• v20.0.0: 16 open issues
• v21.0.0: 11 open issues

Done when

• All open issues have been reviewed for release targeting.
• Issues that belong to planned release trains have a version milestone.
• Issues that are intentionally backlog-only remain unmilestoned with priority:later and correct type/status/area labels.
• Any stale, duplicate, or already-satisfied issues are closed with a short evidence note.

[flyingrobots]

Triage pass complete. Evidence from the live GitHub issue inventory on 2026-06-27:\n\n- Started with 197 open unmilestoned issues.\n- Assigned 29 obvious release-train leaks to milestones: 7 to v19.0.0, 14 to v20.0.0, and 8 to v21.0.0.\n- Remaining unmilestoned backlog: 168 issues.\n- Remaining unmilestoned priority counts: 168 priority:later, 0 priority:next, 0 priority:asap.\n- Remaining unmilestoned status counts: 162 status:available, 6 status:blocked, 0 status:active.\n- Label-axis audit across remaining unmilestoned issues: 0 violations; each has exactly one type, priority, status, and area label.\n\nCurrent release buckets after triage:\n\n- v19.0.0: 23 open / 6 closed.\n- v20.0.0: 30 open / 0 closed.\n- v21.0.0: 19 open / 0 closed.\n\nThe remaining unmilestoned bucket is intentionally backlog-only and queryable by priority:later plus its axis labels.