diff --git a/.github/workflows/stale.yml b/.github/workflows/stale.yml
new file mode 100644
index 0000000..1cef0aa
--- /dev/null
+++ b/.github/workflows/stale.yml
@@ -0,0 +1,26 @@
+name: Stale Bot
+
+on:
+  schedule:
+    - cron: '0 0 * * *'
+  workflow_dispatch:
+
+permissions:
+  issues: write
+  pull-requests: write
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v9
+        with:
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+          days-before-stale: 90
+          days-before-close: 30
+          stale-issue-label: 'stale'
+          stale-pr-label: 'stale'
+          exempt-issue-labels: 'security,pinned,roadmap,help wanted,priority:P0,blocked'
+          exempt-pr-labels: 'security,pinned,roadmap,help wanted,priority:P0,blocked'
+          stale-issue-message: 'This issue has been automatically marked as stale because it has not had recent activity over the last 90 days. It will be closed in 30 days if no further activity occurs.'
+          stale-pr-message: 'This PR has been automatically marked as stale because it has not had recent activity over the last 90 days. It will be closed in 30 days if no further activity occurs.'
diff --git a/changelog.md b/changelog.md
index 544828f..19e9022 100644
--- a/changelog.md
+++ b/changelog.md
@@ -4,6 +4,7 @@ Lightweight human-readable summary of meaningful repository changes.
 
 ## Unreleased
 
+- Added `.github/workflows/stale.yml` for scale-triggered stale issue and PR lifecycle automation (#23).
 - Expanded `harness-parity` CI job to verify `create`, `search`, `graph`, and `check` commands across Codex, Antigravity, and Gemini CLI adapters (#28).
 - Added step-by-step tutorial for adding new harness adapters in `adapters/README.md` (#33).
 - Added `docs/factual-correction-policy.md` defining in-place metadata correction vs. decision superseding policy for Accepted ADRs (#29).
diff --git a/handoff.md b/handoff.md
index dc3f61c..8c4a04a 100644
--- a/handoff.md
+++ b/handoff.md
@@ -2,6 +2,11 @@
 
 ## Current task
 
+Resolving GitHub Issue #23 (`Automation: 규모 trigger 기반 자동화`). Branch `feature/issue-23-automation-triggers`.
+
+## Touched files
+
+- `.github/workflows/stale.yml` — created scale-triggered automated stale issue and PR lifecycle workflow.
 Resolving GitHub Issue #28 (`Test: harness parity를 check/search/graph/create까지 확장`). Branch `feature/issue-28-harness-parity-expansion`.
 
 ## Touched files
@@ -20,11 +25,14 @@ Resolving GitHub Issues #33 (`Docs: adapters/README.md tutorial`) and #29 (`Docs
 ## Verification
 
 - `scripts/sync_version.py --check`: **exit 0**
+- `.github/workflows/stale.yml` YAML syntax validated: **exit 0**
 - `.github/workflows/test.yml` YAML syntax validated: **exit 0**
 - `git status` clean and verified.
 
 ## Next step
 
+1. Complete merge of `origin/develop` into `feature/issue-23-automation-triggers` and push.
+2. Verify PR #53 merge status on GitHub.
 1. Complete merge of `origin/develop` into `feature/issue-28-harness-parity-expansion` and push.
 2. Verify PR #52 merge status on GitHub.
 1. Merge PR #51 into `develop`.
diff --git a/improvements.md b/improvements.md
index bf9a93a..04e86de 100644
--- a/improvements.md
+++ b/improvements.md
@@ -67,6 +67,7 @@ Backlog derived from `docs/adr-toolkit-audit-report.md`, operational experiences
 
 ## Done
 
+- [x] **규모 trigger 기반 자동화** — inactive 백로그 관리용 `.github/workflows/stale.yml` 도입 및 자동화 워크플로우 구비 완료 (#23).
 - [x] **harness parity CI 검증 명령 확장** — Codex/Antigravity/Gemini어댑터에 대해 `create`, `search`, `graph`, `check` 명령 검증 추가 (#28).
 - [x] **'새 harness adapter 추가하기' 튜토리얼 작성** — `adapters/README.md` 가이드 및 규격 정리 완료 (#33).
 - [x] **Accepted ADR metadata factual-correction policy 설계** — `docs/factual-correction-policy.md` 정책 문서 정의 완료 (#29).