[Klaud Cold] Fix signoff-verify parse error: move verifier prompt out of workflow YAML / 修复 signoff-verify 解析错误：将验证器提示词移出 workflow YAML

[functionstackx]

Summary

Fixes the broken workflow file currently on main (Invalid workflow file: .github/workflows/codeowner-signoff-verify.yml — (Line: 237, Col: 19): Exceeded max expression length 21000, e.g. this run). GitHub compiles any ${{ }}-bearing workflow scalar into a single format() expression capped at 21,000 characters; the Check 9 addition in #2155 pushed the inline verifier prompt to ~21,030 compiled characters. Until this lands, the required codeowner-signoff-verify status cannot run for any sign-off.

• .github/codeowner-signoff-verify-prompt.md (new): the full verifier prompt, moved verbatim, with ${{ needs.gate.outputs.* }} / ${{ github.repository }} replaced by ${PR_NUMBER}-style placeholders.
• codeowner-signoff-verify.yml: new "Render verifier prompt" step substitutes those six values with envsubst (template read from the trusted default-branch checkout — same trust level as the workflow itself, never PR-head content) and writes /tmp/codeowner-signoff-verify-prompt.md; the Claude action now gets a tiny static pointer prompt. Largest remaining expression in the file is ~450 chars, so the checklist can keep growing without ever hitting this limit again. A grep guard in the render step fails fast if substitution ever breaks.
• AGENTS.md: checklist ↔ verifier sync rule now points at the template file and warns not to move the prompt back inline.

Verified locally: YAML parses; an expression-length audit of every scalar passes with wide margin; a render simulation substitutes all six placeholders with zero leftovers and preserves the sha-pinned marker, PR #<n> references, and the Check 9 section.

中文说明

修复当前 main 上损坏的 workflow 文件（Exceeded max expression length 21000，见此运行）。GitHub 会将含 ${{ }} 的 workflow 标量编译为单个 format() 表达式，上限 21,000 字符；#2155 新增的 Check 9 使内联提示词达到约 21,030 字符。在本 PR 合并前，必需的 codeowner-signoff-verify 状态检查无法对任何签署运行。

• .github/codeowner-signoff-verify-prompt.md（新增）：完整验证器提示词原样迁入，${{ }} 表达式替换为 ${PR_NUMBER} 等占位符。
• codeowner-signoff-verify.yml：新增 "Render verifier prompt" 步骤，用 envsubst 替换六个动态值（模板来自受信任的默认分支检出，信任级别与 workflow 本身相同，绝不使用 PR head 内容）并写入 /tmp/codeowner-signoff-verify-prompt.md；Claude action 仅接收极短的静态指针提示词。文件中剩余最大表达式约 450 字符，清单今后可任意增长而不会再触及该上限。渲染步骤中的 grep 守卫可在替换失效时立即失败。
• AGENTS.md：清单 ↔ 验证器同步规则改为指向该模板文件，并注明不要将提示词移回内联。

本地已验证：YAML 可解析；对所有标量的表达式长度审计通过且余量充足；渲染模拟替换全部六个占位符、无残留，并保留 sha 固定标记、PR #<n> 引用及 Check 9 小节。

🤖 Generated with Claude Code

[claude]

LGTM — mechanical fix that moves the verifier prompt verbatim to a template file rendered via envsubst, unblocking the required check that's currently failing to parse on main.

Extended reasoning...

Overview

Three-file change to fix a broken required workflow on main. The verifier prompt in .github/workflows/codeowner-signoff-verify.yml overflowed GitHub's 21,000-char cap on ${{ }}-bearing scalars after Check 9 was added in #2155. The prompt is moved verbatim into a new .github/codeowner-signoff-verify-prompt.md template, a new "Render verifier prompt" step runs envsubst on it to substitute six placeholders (REPO, PR_NUMBER, HEAD_SHA, SIGNOFF_AUTHOR, SIGNOFF_KIND, SIGNOFF_FETCH_CMD), and the Claude action receives a 4-line pointer prompt. AGENTS.md is updated to point the checklist↔verifier sync rule at the new template.

Security risks

The workflow is privileged (write perms + secrets: CLAUDE_PAT, ANTHROPIC_API_KEY) and runs on comment triggers, so untrusted content is a real concern. However, the security perimeter is preserved:

• The template is read from the trusted default-branch checkout (ref: ${{ github.event.repository.default_branch }}), same trust level as the workflow file itself — never PR-head content.
• envsubst is passed an explicit allowlist ('${REPO} ${PR_NUMBER} ...') which prevents unintended expansion of any other shell-style tokens in the prompt body.
• GitHub logins (SIGNOFF_AUTHOR) are alphanumeric+hyphen so cannot smuggle shell metachars; SIGNOFF_KIND is one of three hard-coded strings; SIGNOFF_FETCH_CMD is constructed in the gate step from vetted API paths and integer IDs.
• A grep -q "PR #${PR_NUMBER}" guard in the render step fails fast if substitution silently breaks.

Level of scrutiny

Medium — the file touched is a security-sensitive merge gate (CODEOWNER sign-off verification) and CODEOWNER-owned under the * @InferenceX/core catch-all. But the change itself is purely mechanical: the prompt body is unchanged in meaning, only the delivery mechanism moved from an inline YAML scalar to a file rendered by envsubst. The 10 check specifications, the trusted-branch checkout, and the verdict-publishing step are all untouched.

Other factors

The PR fixes a currently-failing required check (Exceeded max expression length 21000 on run 29115095503), so it's unblocking. PR description reports local verification of YAML parse, expression-length audit, and a render simulation that substitutes all six placeholders with zero leftovers. No bugs were found by the bug hunter. Comfortable shadow-approving.