diff --git a/lib/github.mjs b/lib/github.mjs
index 37db350..1f07d9e 100644
--- a/lib/github.mjs
+++ b/lib/github.mjs
@@ -47,15 +47,32 @@ export function repository(b, r) {
   throw err('GITHUB_REPOSITORY_REQUIRED')
 }
 
+// 按分支查 PR：state=all 才能同时命中 open 与已 merged 的历史 PR。
+// 优先 open，其次最近一条（含 merged/closed）——publish/archive 据此复用，绝不重复开 PR。
+export async function findPr(repository, branch, baseBranch) {
+  if (!branch) return null
+  const qs = new URLSearchParams({ state: 'all', head: `${repository.split('/')[0]}:${branch}`, per_page: '20' })
+  const found = await api(`/repos/${repository}/pulls?${qs}`)
+  const list = (Array.isArray(found) ? found : []).filter(p => p && p.number && (!baseBranch || !p.base || !p.base.ref || p.base.ref === baseBranch))
+  if (!list.length) return null
+  const stamp = p => String(p.merged_at || p.closed_at || p.created_at || '')
+  return list.find(p => p.state === 'open') || list.slice().sort((a, c) => stamp(c).localeCompare(stamp(a)))[0]
+}
+
 export async function pr(b, r) {
   const n = Number(b.data.github?.pullRequest)
-  if (!n) throw err('PULL_REQUEST_REQUIRED')
-  return api(`/repos/${repository(b, r)}/pulls/${n}`)
+  if (n) return api(`/repos/${repository(b, r)}/pulls/${n}`)
+  // brief 的 pullRequest 缺失或被早期命令回写清空时，按分支回查并回填，避免归档被 PULL_REQUEST_REQUIRED 卡死
+  const found = await findPr(repository(b, r), b.data.branch, b.data.baseBranch || 'main')
+  if (!found) throw err('PULL_REQUEST_REQUIRED')
+  b.data.github = { ...(b.data.github || {}), pullRequest: found.number, pullRequestUrl: found.html_url || null }
+  return found
 }
 
 export async function ensurePr(x) {
-  const qs = new URLSearchParams({ state: 'open', head: `${x.repository.split('/')[0]}:${x.branch}`, base: x.baseBranch }), found = await api(`/repos/${x.repository}/pulls?${qs}`)
-  if (found[0]) return { pr: found[0], created: false }
+  // 复用而非新建：已 merged 的 PR 同样命中（此前只查 state=open，分支合并后再 publish 会重复开 PR）
+  const existing = await findPr(x.repository, x.branch, x.baseBranch)
+  if (existing) return { pr: existing, created: false }
   try {
     const z = await api(`/repos/${x.repository}/pulls`, { method: 'POST', body: JSON.stringify({ title: x.title, body: x.body, head: x.branch, base: x.baseBranch }) })
     return { pr: z, created: true }
diff --git a/test/cli.test.mjs b/test/cli.test.mjs
index b8a7fb7..3f010f0 100644
--- a/test/cli.test.mjs
+++ b/test/cli.test.mjs
@@ -684,6 +684,41 @@ test('publish pushes normally and creates a PR when none exists', () => {
   } finally { api.close() }
 })
 
+test('publish reuses an already merged PR instead of opening a duplicate', () => {
+  const root = fixture()
+  addOrigin(root)
+  execFileSync('git', ['switch', '-c', 'feat/sample'], { cwd: root })
+  writeFileSync(join(root, 'feature.txt'), 'feature' + String.fromCharCode(10))
+  execFileSync('git', ['add', '--', 'feature.txt'], { cwd: root })
+  execFileSync('git', ['commit', '-m', 'feature'], { cwd: root })
+  // 复现 2026-10-09 事故：PR 已 merged，brief 的 pullRequest 字段被复验回写清空
+  updateBrief(root, data => { data.github.repository = 'owner/repo'; data.branch = 'feat/sample'; data.github.pullRequest = null; data.github.pullRequestUrl = null })
+  const merged = { number: 525, state: 'closed', merged_at: '2026-10-09T11:20:00Z', html_url: 'https://github.test/pulls/525', base: { ref: 'main' } };
+  const api = apiStub([{ method: 'GET', path: '/repos/owner/repo/pulls?', body: [merged] }])
+  try {
+    const args = ['--name', 'sample', '--title', 'Feature']
+    const planned = run(['publish', 'plan', ...args, '--json'], root)
+    const result = run(['publish', 'execute', ...args, '--plan-hash', JSON.parse(planned.stdout).planHash, '--confirm', '--json'], root, { GITHUB_TOKEN: 'token', SHADOW_GITHUB_API_URL: api.url })
+    assert.equal(result.status, 0, result.stderr)
+    const out = JSON.parse(result.stdout)
+    assert.equal(out.data.number, 525)
+    assert.equal(out.data.created, false)
+    assert.deepEqual(api.requests().map(request => request.method), ['GET'])
+    assert.match(readFileSync(join(root, 'shadow-docs', 'changes', 'sample', 'brief.md'), 'utf8'), /"pullRequest": 525/)
+  } finally { api.close() }
+})
+
+test('pr inspect recovers the PR by branch when the brief lost its pullRequest field', () => {
+  const root = fixture()
+  updateBrief(root, data => { data.github.repository = 'owner/repo'; data.github.pullRequest = null; data.branch = 'feat/sample' })
+  const found = { number: 12, state: 'closed', merged_at: '2026-10-09T00:00:00Z', html_url: 'https://github.test/pulls/12', base: { ref: 'main' } };
+  const api = apiStub([{ method: 'GET', path: '/repos/owner/repo/pulls?', body: [found] }])
+  try {
+    const result = run(['pr', 'inspect', '--name', 'sample', '--json'], root, { GITHUB_TOKEN: 'token', SHADOW_GITHUB_API_URL: api.url })
+    assert.equal(result.status, 0, result.stderr)
+    assert.equal(JSON.parse(result.stdout).data.number, 12)
+  } finally { api.close() }
+})
 test('publish defaults the PR body to Closes #N when the brief has an issue', () => {
   const root = fixture()
   addOrigin(root)