diff --git a/.github/dependabot-for-sync.yml b/.github/dependabot-for-sync.yml
index f090c50..82b959a 100644
--- a/.github/dependabot-for-sync.yml
+++ b/.github/dependabot-for-sync.yml
@@ -12,9 +12,14 @@ updates:
     ignore:
       - dependency-name: "the-pr-agent/pr-agent"
     groups:
+      tagpr:
+        patterns:
+          - "Songmu/tagpr"
       dependencies:
         patterns:
           - "*"
+        exclude-patterns:
+          - "Songmu/tagpr"
     open-pull-requests-limit: 20
 
   - package-ecosystem: gomod
diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 6773f7b..eac731e 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -10,9 +10,14 @@ updates:
     cooldown:
       default-days: 7
     groups:
+      tagpr:
+        patterns:
+          - "Songmu/tagpr"
       dependencies:
         patterns:
           - "*"
+        exclude-patterns:
+          - "Songmu/tagpr"
     open-pull-requests-limit: 20
 
   - package-ecosystem: gomod
diff --git a/.github/files-sync-config.yaml b/.github/files-sync-config.yaml
index 887c6bf..c016cc8 100644
--- a/.github/files-sync-config.yaml
+++ b/.github/files-sync-config.yaml
@@ -6,6 +6,7 @@ settings:
 patterns:
   - files:
       - .github/workflows/pr-agent.yml
+      - .github/workflows/dependabot-auto-merge.yml
       - from: .github/dependabot-for-sync.yml
         to: .github/dependabot.yml
       - .golangci.yml
diff --git a/.github/workflows/dependabot-auto-merge.yml b/.github/workflows/dependabot-auto-merge.yml
new file mode 100644
index 0000000..13c2356
--- /dev/null
+++ b/.github/workflows/dependabot-auto-merge.yml
@@ -0,0 +1,134 @@
+name: Auto-merge tagpr updates
+
+on:
+  workflow_run:
+    workflows: [test, Tests, CI]
+    types: [completed]
+
+permissions: {}
+
+concurrency:
+  group: tagpr-auto-merge-${{ github.event.workflow_run.head_branch }}
+  cancel-in-progress: false
+
+jobs:
+  merge:
+    if: >-
+      github.repository_owner == 'monitoring-forge' &&
+      github.event.workflow_run.conclusion == 'success' &&
+      github.event.workflow_run.head_repository.full_name == github.repository
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    permissions:
+      actions: read
+      contents: read
+      pull-requests: read
+    steps:
+      - name: Verify tests and tagpr-only changes
+        id: verify
+        uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8
+        with:
+          script: |
+            const {owner, repo} = context.repo;
+            const fullName = `${owner}/${repo}`;
+            const eventRun = context.payload.workflow_run;
+            const {data: run} = await github.rest.actions.getWorkflowRun({owner, repo, run_id: eventRun.id});
+            if (run.status !== 'completed' || run.conclusion !== 'success' ||
+                run.run_attempt !== eventRun.run_attempt ||
+                !['push', 'pull_request'].includes(run.event) ||
+                run.head_repository?.full_name !== fullName ||
+                !['.github/workflows/test.yml', '.github/workflows/ci.yml'].includes(run.path?.split('@')[0])) {
+              core.info('Skip: no current successful test run in this repository.');
+              return;
+            }
+            const prs = await github.paginate(github.rest.pulls.list, {
+              owner, repo, state: 'open', head: `${owner}:${run.head_branch}`, per_page: 100,
+            });
+            for (const candidate of prs) {
+              const {data: pr} = await github.rest.pulls.get({owner, repo, pull_number: candidate.number});
+              if (pr.user.login !== 'dependabot[bot]' || pr.draft ||
+                  pr.head.repo?.full_name !== fullName || pr.head.sha !== run.head_sha ||
+                  pr.base.ref !== context.payload.repository.default_branch) continue;
+
+              // Inspect data only: never check out or execute code from the PR.
+              const files = await github.paginate(github.rest.pulls.listFiles, {
+                owner, repo, pull_number: pr.number, per_page: 100,
+              });
+              if (!files.length || files.length !== pr.changed_files) continue;
+              let tagprOnly = true;
+              const normalize = text => text.replace(
+                /^(\s*(?:-\s+)?uses:\s*Songmu\/tagpr@)[a-zA-Z0-9._/-]+(?:[ \t]+#[^\r\n]*)?[ \t]*$/gm,
+                '$1<ref>',
+              );
+              for (const file of files) {
+                if (file.status !== 'modified' || !/^\.github\/workflows\/[^/]+\.ya?ml$/.test(file.filename)) {
+                  tagprOnly = false;
+                  break;
+                }
+                const read = async ref => {
+                  const {data} = await github.rest.repos.getContent({owner, repo, path: file.filename, ref});
+                  if (data.type !== 'file' || data.encoding !== 'base64') throw new Error('Unexpected file response');
+                  return Buffer.from(data.content, 'base64').toString('utf8');
+                };
+                const before = await read(pr.base.sha);
+                const after = await read(pr.head.sha);
+                if (before === after || normalize(before) !== normalize(after)) {
+                  tagprOnly = false;
+                  break;
+                }
+              }
+              if (!tagprOnly) {
+                core.info(`Skip #${pr.number}: changes are not limited to Songmu/tagpr references.`);
+                continue;
+              }
+
+              // Reject a superseded success or a pending/failed rerun for this exact head.
+              const runs = await github.paginate(github.rest.actions.listWorkflowRuns, {
+                owner, repo, workflow_id: run.workflow_id, head_sha: pr.head.sha,
+                branch: pr.head.ref, event: run.event, per_page: 100,
+              });
+              const latest = runs.sort((a, b) => b.id - a.id)[0];
+              if (!latest || latest.id !== run.id || latest.status !== 'completed' ||
+                  latest.conclusion !== 'success' || latest.run_attempt !== run.run_attempt) continue;
+
+              const {data: repository} = await github.rest.repos.get({owner, repo});
+              const method = repository.allow_merge_commit ? 'merge' :
+                repository.allow_squash_merge ? 'squash' : repository.allow_rebase_merge ? 'rebase' : null;
+              if (!method) throw new Error('No merge method is enabled');
+              core.setOutput('pull-number', pr.number);
+              core.setOutput('head-sha', pr.head.sha);
+              core.setOutput('merge-method', method);
+              return;
+            }
+
+      - name: Generate repository-scoped merge token
+        if: steps.verify.outputs.pull-number != ''
+        id: app-token
+        uses: actions/create-github-app-token@bcd2ba49218906704ab6c1aa796996da409d3eb1 # v3
+        with:
+          client-id: ${{ secrets.CLIENT_ID }}
+          private-key: ${{ secrets.APP_PRIVATE_KEY }}
+          owner: ${{ github.repository_owner }}
+          repositories: ${{ github.event.repository.name }}
+          permission-contents: write
+          permission-pull-requests: write
+
+      - name: Merge with GitHub App to trigger push workflows
+        if: steps.verify.outputs.pull-number != ''
+        uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8
+        env:
+          PR_NUMBER: ${{ steps.verify.outputs.pull-number }}
+          HEAD_SHA: ${{ steps.verify.outputs.head-sha }}
+          MERGE_METHOD: ${{ steps.verify.outputs.merge-method }}
+        with:
+          github-token: ${{ steps.app-token.outputs.token }}
+          script: |
+            const {owner, repo} = context.repo;
+            const pull_number = Number(process.env.PR_NUMBER);
+            // The App token triggers push workflows; the SHA rejects a newer push.
+            const {data: result} = await github.rest.pulls.merge({
+              owner, repo, pull_number, sha: process.env.HEAD_SHA,
+              merge_method: process.env.MERGE_METHOD,
+            });
+            if (!result.merged) throw new Error(result.message);
+            core.info(`Merged #${pull_number}: ${result.sha}`);
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..f2ab39c
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,15 @@
+name: test
+on:
+  push:
+    branches:
+      - '**'
+  pull_request:
+permissions:
+  contents: read
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+      - name: Test auto-merge policy
+        run: node --test tests/*.test.cjs
diff --git a/README.md b/README.md
index fb3b762..71d7918 100644
--- a/README.md
+++ b/README.md
@@ -5,7 +5,53 @@
 ## 対象ファイル
 
 - .github/workflows/pr-agent.yml
+- .github/workflows/dependabot-auto-merge.yml
 - .github/dependabot.yml
 - .golangci.yml
 
 
+## Songmu/tagpr 更新の自動マージ
+
+`.github/workflows/dependabot-auto-merge.yml` を各リポジトリに同期します。
+Dependabot の GitHub Actions 更新では `Songmu/tagpr` を専用の `tagpr` グループに分離し、
+他の依存関係を含む PR は自動マージしません。既存の `dependencies` グループの PR でも、
+実際の差分が tagpr の参照更新だけなら対象になります。メジャー更新も対象です。
+
+次の条件をすべて満たす場合、テスト完了後にマージします。
+
+- PR の作成者が `dependabot[bot]` で、同じリポジトリのブランチからデフォルトブランチへの PR である。
+- `.github/workflows/test.yml` または `.github/workflows/ci.yml` の `test` / `Tests` / `CI` が成功した。
+- 成功した実行が PR の最新コミットに対応し、再実行や新しい実行で置き換えられていない。
+- 変更ファイルは既存の `.github/workflows/*.yml` / `*.yaml` のみで、変更内容は `uses: Songmu/tagpr@...` の参照と同行のコメントのみである。
+
+`workflow_run` でテスト終了後に起動し、PR のコード・成果物・キャッシュは実行しません。
+GitHub API にマージ対象のコミット SHA を渡し、判定後に追加されたコミットのマージを防ぎます。
+App をブランチ保護・ruleset の bypass 対象に追加する必要はありません。既存の保護を維持してください。保護設定などでマージが拒否された場合は
+Actions の実行が失敗します。条件を解消した後、対象 PR のテストを再実行してください。
+GitHub の「Allow auto-merge」設定には依存しません。
+
+### 導入
+
+事前に、既存 GitHub App を全対象リポジトリへインストールし、Actions Secrets の
+`CLIENT_ID` と `APP_PRIVATE_KEY` を各リポジトリから利用可能にしてください。
+Organization Secrets の場合は対象リポジトリへの公開範囲も確認してください。
+App は Contents / Pull requests の読み書き権限を使用します。Issues の権限は不要です。
+Actions の読み取りは標準の `GITHUB_TOKEN` で行うため、App への追加権限は不要です。
+
+1. この変更を `main` にマージし、通常の tagpr リリースを行います。
+2. リリース時の既存のファイル同期により、36リポジトリに同期 PR が作成されます。
+3. 各同期 PR をマージすると有効になります。`github-common` 自身はこの変更のマージで有効になります。
+4. すでにテストが終了している Dependabot PR は、導入後にテストを再実行すると判定されます。
+
+テストが存在しない、または成功しない場合は自動マージされません。
+テストと差分の確認には読み取り専用の `GITHUB_TOKEN` を使い、対象が見つかった場合のみ、
+現在のリポジトリに限定した GitHub App トークンを発行してマージします。
+そのため、マージ後の `push` を起点とするテスト・tagpr も起動します。
+tagpr 側のトークン設定は変更しません。Secrets が未設定の場合はマージせず失敗します。
+他の必須チェックがテストより遅れて終了する場合も、完了後にテストを再実行してください。
+
+### 検証
+
+`github-common` で `node --test tests/*.test.cjs` を実行します。
+実際に同期するワークフロー内のスクリプトを、GitHub API の応答を模擬して検証します。
+この検証用の `test.yml` と `tests/` は他のリポジトリには同期しません。
diff --git a/tests/dependabot-auto-merge.test.cjs b/tests/dependabot-auto-merge.test.cjs
new file mode 100644
index 0000000..f0e7dac
--- /dev/null
+++ b/tests/dependabot-auto-merge.test.cjs
@@ -0,0 +1,79 @@
+const {test} = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const workflow = fs.readFileSync('.github/workflows/dependabot-auto-merge.yml', 'utf8');
+const scripts = [...workflow.matchAll(/          script: \|\n((?:            [^\n]*\n|\n)*)/g)]
+  .map(match => match[1].split('\n').map(line => line.slice(12)).join('\n'));
+assert.equal(scripts.length, 2);
+const AsyncFunction = Object.getPrototypeOf(async function(){}).constructor;
+const execute = new AsyncFunction('github', 'context', 'core', scripts[0]);
+const merge = new AsyncFunction('github', 'context', 'core', 'process', scripts[1]);
+
+async function scenario(change = () => {}) {
+  const fullName = 'monitoring-forge/flagrun';
+  const run = {id: 1, workflow_id: 2, run_attempt: 1, status: 'completed', conclusion: 'success',
+    event: 'push', head_sha: 'tested', head_branch: 'dependabot/github_actions/dependencies-123',
+    head_repository: {full_name: fullName}, path: '.github/workflows/test.yml'};
+  const pr = {number: 34, user: {login: 'dependabot[bot]'}, draft: false, changed_files: 1,
+    head: {sha: 'tested', ref: run.head_branch, repo: {full_name: fullName}}, base: {ref: 'main', sha: 'base'}};
+  const state = {run, eventRun: {...run}, pr, latest: {...run},
+    files: [{filename: '.github/workflows/tagpr.yml', status: 'modified'}],
+    before: 'steps:\n  - uses: Songmu/tagpr@old # v1\n    env:\n      TOKEN: example\n',
+    after: 'steps:\n  - uses: Songmu/tagpr@new # v2\n    env:\n      TOKEN: example\n',
+    repository: {allow_merge_commit: true}, merged: []};
+  change(state);
+  const github = {rest: {
+    actions: {getWorkflowRun: async () => ({data: state.run}), listWorkflowRuns: 'runs'},
+    pulls: {list: 'prs', listFiles: 'files', get: async () => ({data: state.pr}),
+      merge: async args => {state.merged.push(args); return {data: {merged: true, sha: 'merged'}};}},
+    repos: {get: async () => ({data: state.repository}), getContent: async args => ({data: {
+      type: 'file', encoding: 'base64', content: Buffer.from(args.ref === 'base' ? state.before : state.after).toString('base64'),
+    }})},
+  }, paginate: async (method) => ({runs: [state.latest], prs: [state.pr], files: state.files})[method]};
+  const context = {repo: {owner: 'monitoring-forge', repo: 'flagrun'},
+    payload: {workflow_run: state.eventRun, repository: {default_branch: 'main'}}};
+  const outputs = {};
+  const core = {info() {}, setOutput(key, value) {outputs[key] = String(value);}};
+  const appGithub = {rest: {pulls: {merge: github.rest.pulls.merge}}};
+  github.rest.pulls.merge = async () => {throw new Error('Default token must not merge');};
+  await execute(github, context, core);
+  if (outputs['pull-number']) {
+    await merge(appGithub, context, core, {env: {
+      PR_NUMBER: outputs['pull-number'], HEAD_SHA: outputs['head-sha'], MERGE_METHOD: outputs['merge-method'],
+    }});
+  }
+  return state.merged;
+}
+test('tagpr-only grouped update merges exactly the tested SHA', async () => {
+  const [merge] = await scenario();
+  assert.equal(merge.sha, 'tested'); assert.equal(merge.pull_number, 34); assert.equal(merge.merge_method, 'merge');
+});
+test('pull_request CI and squash-only repositories are supported', async () => {
+  const [merge] = await scenario(s => {s.run.event = 'pull_request'; s.run.path = '.github/workflows/ci.yml';
+    s.repository = {allow_squash_merge: true};});
+  assert.equal(merge.merge_method, 'squash');
+});
+for (const [name, change] of Object.entries({
+  'failed tests': s => {s.run.conclusion = 'failure';},
+  'pending rerun': s => {s.run.status = 'in_progress';},
+  'stale attempt': s => {s.run.run_attempt = 2;},
+  'unrelated workflow': s => {s.run.path = '.github/workflows/tagpr.yml';},
+  'untrusted event': s => {s.run.event = 'workflow_dispatch';},
+  'fork run': s => {s.run.head_repository = {full_name: 'other/flagrun'};},
+  'human author': s => {s.pr.user.login = 'human';},
+  'draft': s => {s.pr.draft = true;},
+  'fork PR': s => {s.pr.head.repo.full_name = 'other/flagrun';},
+  'new head after testing': s => {s.pr.head.sha = 'untested';},
+  'non-default base': s => {s.pr.base.ref = 'other';},
+  'additional dependency': s => {s.before += '  - uses: actions/checkout@old\n'; s.after += '  - uses: actions/checkout@new\n';},
+  'changed executable content': s => {s.after += '  - run: echo unsafe\n';},
+  'indentation change': s => {s.after = s.after.replace('  - uses:', '    - uses:');},
+  'non-workflow file': s => {s.files[0].filename = 'go.mod';},
+  'renamed file': s => {s.files[0].status = 'renamed';},
+  'truncated file list': s => {s.pr.changed_files = 2;},
+  'empty diff': s => {s.files = []; s.pr.changed_files = 0;},
+  'newer test run': s => {s.latest.id = 2;},
+  'latest failed': s => {s.latest.conclusion = 'failure';},
+  'latest pending': s => {s.latest.status = 'in_progress';},
+  'latest attempt changed': s => {s.latest.run_attempt = 2;},
+})) test(`does not merge: ${name}`, async () => assert.deepEqual(await scenario(change), []));