docs(agents): make AGENTS.md the shared contract for every executor

[jasonhnd]

Closes #662

What changed

Applied the revised Issue #662 appendix to AGENTS.md, including all four review fixes (merge authority + preconditions, explicit empty PUBLIC_* overrides incl. PUBLIC_CF_BEACON_TOKEN / PUBLIC_GOOGLE_ADS_ID, Chromium install step, TOOLCHAIN §10.1 note). Updated exactly one line each in docs/WORKFLOW.md and CONTRIBUTING.md to align preview merge authority; the WORKFLOW promotion section is unchanged. Added the prescribed CHANGELOG entry.

Commits:

• 00f2a09a docs(agents): make AGENTS.md the shared contract for every executor
• 4987f7c6 docs(changelog): note AGENTS.md shared executor contract
• 461c07c0 docs(agents): apply review fixes from docs(agents): make AGENTS.md the shared contract for every executor #663 review
• e72afe42 docs: align preview merge lines with supervisor authority

Verification

=== diff AGENTS.md /tmp/agents-target.md ===
diff_exit=0
=== bun run check:docs-links ===
$ bun scripts/check-doc-links.cjs
[check-doc-links] OK — 58 tracked Markdown files, 102 local link/image target(s)
docs_links_exit=0
=== git diff --stat origin/preview ===
 AGENTS.md        | 148 +++++++++++++++++++++++++++++++++++++++++++++++++------
 CHANGELOG.md     |   1 +
 CONTRIBUTING.md  |   2 +-
 docs/WORKFLOW.md |   2 +-
 4 files changed, 136 insertions(+), 17 deletions(-)
=== grep -c human merge ===
docs/WORKFLOW.md:1
CONTRIBUTING.md:0

diff printed nothing (diff_exit=0). CONTRIBUTING.md and docs/WORKFLOW.md are each a one-line replacement (2 +- is one deletion and one insertion). The remaining human merge hit is the promotion sentence in docs/WORKFLOW.md.

Not done / notes

• This PR did not re-run the full acceptance chain (test, typecheck, build, Playwright). The change is documentation.
• The .env.local measurement (unset still emits the production gtag snippet; explicit empty exports do not) was done by the supervisor and is recorded in Issue docs(agents): make AGENTS.md the shared contract for every executor (branches, delivery, forbidden ops, acceptance, repo constraints) #662, section "Revision 2026-09-25".

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1 Skipped Deployment

Project	Deployment	Actions	Updated
jobs	Ignored	Preview	Sep 25, 2026 12:41am UTC

[jasonhnd]

Review fixes from the updated Issue #662 (Revision 2026-09-25) are on docs/agents-contract.

Commits

• 461c07c0 docs(agents): apply review fixes from docs(agents): make AGENTS.md the shared contract for every executor #663 review
• e72afe42 docs: align preview merge lines with supervisor authority

CHANGELOG.md was not changed again. The existing Unreleased bullet stays as it was.

What changed

1. AGENTS.md was replaced with the revised appendix, extracted with the same gh + awk fence filter. Not reworded.
2. docs/WORKFLOW.md standard-flow step 5, third bullet: the whole line that said human merge now names the supervisor (owner, or a supervising agent the owner has delegated preview merges to) and says the executor does not merge. The promotion section (「Owner が production 反映を承認して human merge する」) is unchanged.
3. CONTRIBUTING.md step 4: the whole line was replaced with the Issue's text block, including that main promotion is merged by the owner.

Verification

=== diff AGENTS.md /tmp/agents-target.md ===
diff_exit=0
=== sed extraction cross-check ===
sed_diff_exit=0
=== bun run check:docs-links ===
$ bun scripts/check-doc-links.cjs
[check-doc-links] OK — 58 tracked Markdown files, 102 local link/image target(s)
docs_links_exit=0
=== git diff --stat origin/preview ===
 AGENTS.md        | 148 +++++++++++++++++++++++++++++++++++++++++++++++++------
 CHANGELOG.md     |   1 +
 CONTRIBUTING.md  |   2 +-
 docs/WORKFLOW.md |   2 +-
 4 files changed, 136 insertions(+), 17 deletions(-)
=== grep -c human merge ===
docs/WORKFLOW.md:1
CONTRIBUTING.md:0
=== git diff origin/preview -- docs/WORKFLOW.md CONTRIBUTING.md ===
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 1fbbfc04..19900a65 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -7,7 +7,7 @@ Issue と Pull Request を歓迎します。非自明な変更は、実装前に
 1. 最新の `preview` から topic branch を作る。
 2. 変更と必要なテスト・文書を同じ branch に含める。
 3. `preview` を base に PR を作り、関連 Issue を `Closes #...` でリンクする。
-4. Repository checks の rollout 完了後は `quality`（GitHub UI では `CI / quality`）と `Vercel` を通し、review conversation をすべて解決してから human merge を行う。
+4. Repository checks の rollout 完了後は `quality`（GitHub UI では `CI / quality`）と `Vercel` を通し、review conversation をすべて解決してから、監督者（オーナー、またはオーナーが `preview` への merge を委任した監督 agent）が diff と独立レビューを確認して merge する。実装担当は merge しない。`main` への promotion はオーナー本人が承認して merge する。

 通常の変更を `main` へ直接送らないでください。`main` は production branch であり、`preview → main` の promotion PR だけを受け付けます。

diff --git a/docs/WORKFLOW.md b/docs/WORKFLOW.md
index 381a14dc..f474ee43 100644
--- a/docs/WORKFLOW.md
+++ b/docs/WORKFLOW.md
@@ -35,7 +35,7 @@ Issue、PR、commit message、`docs/` は **英語または日本語のみ**で
 5. **PR を作る**
    - Base branch は `preview` とし、Issue を `Closes #...` でリンクする。
    - 変更内容、文書/baseline 影響、実行した検証を本文に残す。
-   - `quality`（GitHub UI では `CI / quality`）と `Vercel` が成功し、review conversation がすべて解決してから human merge する。
+   - `quality`（GitHub UI では `CI / quality`）と `Vercel` が成功し、review conversation がすべて解決してから、監督者（オーナー、またはオーナーが `preview` への merge を委任した監督 agent）が diff と独立レビューを確認して merge する。実装担当（executor）は merge しない。

 ## 公開境界

diff printed nothing (diff_exit=0). The Issue's sed extraction of the appendix also matched (sed_diff_exit=0). CONTRIBUTING.md and docs/WORKFLOW.md are each a one-line replacement (2 +- is one deletion and one insertion). The remaining human merge hit is the promotion sentence in docs/WORKFLOW.md.

Notes

• The .env* measurement in the Issue was not repeated here. PUBLIC_CF_BEACON_TOKEN, PUBLIC_GA4_MEASUREMENT_ID, and PUBLIC_GOOGLE_ADS_ID are read in src/layouts/BaseLayout.astro.
• No other question about the revised appendix text.