CI: ROOT_README_008_SYNC_GATE — drift guard for README 008-SelfHostProbe row

[PurHur]

Problem

#2207 / #2217 add examples/008-SelfHostProbe and wire the examples ladder. Root README.md shipped-examples table can drift (wrong VM/AOT columns, missing row) without failing CI — same class of bug as #2017 (006) and #1924 (005).

Important: Do not add a second checker script. SSOT is already script/check-root-readme-sync.php (#1832, #1525) with per-example env slices (ROOT_README_006_SYNC_GATE, ROOT_README_007_SYNC_GATE).

Goal

Extend script/check-root-readme-sync.php (not a new check-root-readme-008-sync.php) to assert:

1. README.md contains 008-SelfHostProbe row when examples/README.md documents it
2. VM column shows ✅ (or documented opt-in) — AOT column — / optional
3. No stale “missing 008” while examples ladder is green

Wire gate:

• ROOT_README_008_SYNC_GATE=0 default in script/ci-defaults.env
• ci_run_inventory_checks in script/ci-common.sh (same hook as Docs: ROOT_README shipped-examples table — verify 006-FileUploadWeb row sync #2017 / Docs: ROOT_README + examples README row for 007-ThrowsWeb #2094)
• Default-on follow-up after Examples: Wire 008-SelfHostProbe into README ladder + discovery checks #2217 green

Implementation hints

File	Action
script/check-root-readme-sync.php	Add 008 row checks mirroring 005–007 blocks (~L68–L95)
script/ci-common.sh	ROOT_README_008_SYNC_GATE=1 branch
script/ci-defaults.env	Export gate default 0
test/unit/RootReadmeSyncTest.php	Fixture README snippet
test/unit/CiScriptsTest.php	Document gate in ci-matrix expectations
docs/local-ci-matrix.md	Row for ROOT_README_008_SYNC_GATE

Example assertion sketch

if (str_contains($examples, '008-SelfHostProbe') && !str_contains($body, '008-SelfHostProbe')) {
    $errors[] = 'README.md: missing 008-SelfHostProbe row (#2229)';
}

Acceptance criteria

php script/check-root-readme-sync.php
ROOT_README_008_SYNC_GATE=1 ./script/ci-fast.sh

Harness:

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php script/check-root-readme-sync.php'

Dependencies

• Examples: 008-SelfHostProbe — presenter ladder for bootstrap M0–M4 gates #2207 ✅ — example directory
• Examples: Wire 008-SelfHostProbe into README ladder + discovery checks #2217 — README row + discovery (blocker for default-on flip)
• Docs: ROOT_README_009 + DEVELOPMENT_STATUS_009 sync drift gates #2353 — parallel 009 row (extend same script in one PR if convenient)

Links

• Docs: ROOT_README shipped-examples table — verify 006-FileUploadWeb row sync #2017 / Docs: ROOT_README shipped-examples table — add 005-SessionsWeb row #1924 / Docs: ROOT_README + examples README row for 007-ThrowsWeb #2094 README sync pattern · ROADMAP 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 Phase 4/5