DevEx: Close stale m2-spine-unit issues when file already in compiler_lib_spine_smoke

[PurHur]

Problem

146 open issues labeled m2-spine-unit, but master spine smoke already has 569/586 units — only ~17 inventory files remain.

Many per-file issues were filed in batch 65–67 before corresponding PRs landed (#1794, #1804, #1805, etc.). The open-issue count overstates remaining M2 work and clutters the North Star 2 timeline (#1492, #1419).

Goal

One maintenance PR (or scripted batch) that:

1. Parses test/selfhost/compiler_lib_spine_smoke/main.php for all require_once paths
2. Finds open m2-spine-unit issues whose title references a path already in the spine
3. Closes them with comment: Already in spine smoke on master (569/586); tracked on #1419
4. Leaves truly-open issues for the remaining 17 files

Optional: add script/check-m2-spine-issue-hygiene.php + opt-in gate (mirror #1802 drift guard pattern).

Acceptance criteria

• Open m2-spine-unit count ≈ remaining inventory gap (≤20)
• M2 spine growth: batch tracker (compiler_lib_spine_smoke → full inventory) #1419 / Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492 footers updated after bulk close
• No duplicate re-open of closed issues without new blockers

Verification

gh issue list --state open --label m2-spine-unit --limit 500 | wc -l   # target ≤20
grep -c require_once test/selfhost/compiler_lib_spine_smoke/main.php     # 569

Local/Docker only — no GitHub Actions.

Links

• Batch tracker M2 spine growth: batch tracker (compiler_lib_spine_smoke → full inventory) #1419
• Per-file index M2 wave 2: Grow compiler_lib_spine_smoke toward full vm.php inventory #1497
• Epic Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492
• ROADMAP 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 Phase 5 Self-host