diff --git a/ .gitea / workflows/cd.yaml b/ .gitea / workflows/cd.yaml
deleted file mode 100644
index 7b9122c..0000000
--- a/ .gitea / workflows/cd.yaml	
+++ /dev/null
@@ -1,17 +0,0 @@
-name: CD
-on:
-  push:
-    branches:
-    - master
-jobs:
-  release-tag:
-    name: Release Tag
-    runs-on: ubuntu
-    steps:
-    - name: Release Tag
-      uses: https://gitea.jsc.idv.tw/composite-actions/release-tag@${{ vars.ACTION_VERSION_CALCULATE_VERSION }}
-      with:
-        gitea_token: ${{ secrets.GITEA_TOKEN }}
-        gitea_release: ${{ vars.ACTION_GITEA_RELEASE_VERSION }}
-        version_calculate: ${{ vars.ACTION_VERSION_CALCULATE_VERSION }}
-        release_cleanup: ${{ vars.ACTION_RELEASE_CLEANUP_VERSION }}
diff --git a/ .gitea / workflows/ci.yaml b/ .gitea / workflows/ci.yaml
deleted file mode 100644
index c80bf56..0000000
--- a/ .gitea / workflows/ci.yaml	
+++ /dev/null
@@ -1,17 +0,0 @@
-name: CI
-on:
-  pull_request:
-    branches-ignore:
-    - master
-    types: [opened, synchronize]
-permissions:
-  contents: write
-  pull-requests: write
-  issues: write
-jobs:
-  ai-code-review:
-    name: Code Review 
-    runs-on: ubuntu
-    steps:
-    - name: Code Review
-      uses: https://gitea.jsc.idv.tw/composite-actions/opencode-code-review@${{ vars.ACTION_AI_CODE_REVIEW_VERSION }}
diff --git a/.gitea/ai-review/exclusions.json b/.gitea/ai-review/exclusions.json
new file mode 100644
index 0000000..bc5fc6a
--- /dev/null
+++ b/.gitea/ai-review/exclusions.json
@@ -0,0 +1,128 @@
+[
+  {
+    "location": "app/lib/gitea.js:28",
+    "role": "Assassin",
+    "original_finding": "Gitea API 請求在 headers 中直接放入了 `this.token`，若來源於不可信輸入且未經驗證，將導致 token 洩漏風險。",
+    "reason": "token 來自受信任的 `gitea.token`（CI 自動注入）而非使用者輸入；`_request` 從未將 headers 或 request 物件輸出到日誌，無實際洩漏路徑。錯誤訊息可能夾帶 token 的真正風險已於 index.js 頂層 catch 以 maskSecrets 遮蔽處理。"
+  },
+  {
+    "location": "app/lib/gitea.js:52",
+    "role": "Mage",
+    "original_finding": "findOpenPull 僅撈取前 50 個 PR，數量眾多可能導致重複建立；且 _request GET 未對回傳 json 結構嚴格驗證。",
+    "reason": "重複建立由 Gitea 在 POST 時回傳 422/409 阻擋，findOpenPull 僅在收到 422/409 後用於查回既有 PR 編號（fallback），分頁與否不影響是否重複建立。JSON 結構已透過 `if (!ok || !Array.isArray(json)) return null` 與 `_request` 的 try/catch 防禦驗證。"
+  },
+  {
+    "location": "app/lib/git.js:52",
+    "role": "Assassin",
+    "original_finding": "使用不可信的 remoteUrl 進行 fetch 操作存在 git 協定漏洞風險，建議驗證 remoteUrl 是否為預期 Gitea 網域。",
+    "reason": "remoteUrl 由 `${serverUrl}/${owner}/${repo}.git` 組成，serverUrl 來自受信任的 `gitea.server_url`（CI 環境變數），並非任意使用者輸入；且已使用 `--no-tags` 限制 refspec。容器基底為 node:20-bookworm-slim，git 版本為近期版本。"
+  },
+  {
+    "location": "app/lib/git.js:63",
+    "role": "Rogue",
+    "original_finding": "getCommitMessages 使用 `git log --max-count=50`，數量可能不足或過多。",
+    "reason": "50 筆為 PR 摘要的合理預設上限，非缺陷；改用 `--since` 屬使用場景偏好調整，無明確需求佐證，不在本次修復範圍。"
+  },
+  {
+    "location": "app/lib/util.js:14",
+    "role": "Rogue",
+    "original_finding": "run 函式 maxBuffer 設為 64MB，git diff 內容極大時易引發 OOM，建議改用 stream。",
+    "reason": "run() 採同步 spawnSync 為刻意設計（所有呼叫端皆同步取用 result.stdout）；maxBuffer 為上限保護而非預先配置，僅在輸出達該量時才佔用；傳給 opencode 的 diff 已於 index.js 以 maxDiffChars 截斷。改為 stream 屬大規模架構重構，牽涉設計取捨。"
+  },
+  {
+    "location": "app/lib/git.js:39, 52",
+    "role": "Mage",
+    "original_finding": "多次使用 `git config --global` 修改全域設定，可能導致 ~/.gitconfig 無限膨脹、污染環境；safe.directory 使用萬用字元 `*` 過於寬鬆，建議改用 --local。",
+    "reason": "action 於每次執行皆在全新且即拋的 Docker 容器內運行，~/.gitconfig 不跨執行保留，無「無限膨脹」問題。safe.directory 基於安全考量 git 刻意忽略 repo-local 設定，必須寫在 global/system，無法改用 `--local`；在 owner 不可預期的 CI checkout 工作區使用 `*` 是 runner 的標準做法（如 actions/checkout 亦同）。user.name/email 已使用 --local。"
+  },
+  {
+    "location": "app/index.js:183",
+    "role": "Assassin",
+    "original_finding": "錯誤處理中的 maskSecrets 基於字串取代，可能無法處理所有 Token 變體導致敏感資訊洩漏；建議禁止輸出原始錯誤物件。",
+    "reason": "maskSecrets 以子字串比對取代，能涵蓋 token 出現於錯誤訊息的各處（含 URL 內嵌 `oauth2:<token>@`），實際洩漏向量（http.extraheader 帶入的原始 token）已被遮蔽。URL 編碼/base64 變體不會出現在本專案的錯誤路徑；完全禁止輸出 err.stack 會嚴重損及 CI 除錯能力，取捨上以遮蔽 token 為宜。"
+  },
+  {
+    "location": "app/index.js:7",
+    "role": "Leo",
+    "original_finding": "函式 main() 承擔過多責任，違反單一職責原則，建議抽離 ConflictManager 並封裝 Gitea API 互動。",
+    "reason": "屬主觀重構偏好而非缺陷；程式已分層為 Git／GiteaClient／OpenCode 三個職責清楚的類別，main() 僅負責編排流程，長度與複雜度可控，無立即重構必要。"
+  },
+  {
+    "location": "app/index.js:37",
+    "role": "Rogue",
+    "original_finding": "在 ahead 為 0 時，仍執行昂貴的 diff 採集與分析；建議先執行 countAheadCommits，若 ahead === 0 則直接終止。",
+    "reason": "現有程式已於 `countAheadCommits` 後立即檢查，`if (ahead === 0) { ...; return; }`（index.js:28-32）早於 diff 採集（index.js:36 起）就終止，與建議行為一致，屬誤報。"
+  },
+  {
+    "location": "app/lib/opencode.js:180",
+    "role": "Assassin",
+    "original_finding": "AI 模型產生的 PR 描述未經 sanitization，易遭 Prompt Injection 導致 Stored XSS 攻擊；建議在 extractResult 對 obj.description 使用 HTML Sanitizer。",
+    "reason": "description 以 Markdown 文字經 API 寫入 Gitea PR body，HTML 的消毒由 Gitea 渲染端負責（Gitea 對使用者內容套用 HTML sanitizer policy），非本 action 職責。description 是 Markdown 而非 HTML，在 client 端套用 HTML Sanitizer 反而會破壞合法的 Markdown 內容。"
+  },
+  {
+    "location": "app/lib/opencode.js:154",
+    "role": "Leo",
+    "original_finding": "summarize 函式使用 5 分鐘固定 timeout，大型 diff 可能導致分析失敗；建議改為可配置或依 diff 大小動態計算。",
+    "reason": "送入 opencode 的 diff 已於 index.js 以 maxDiffChars（60000 字元）截斷，prompt 大小有上限，5 分鐘對此規模輸入相當充裕；timeout 可配置屬增強而非缺陷。"
+  },
+  {
+    "location": "app/lib/opencode.js:127",
+    "role": "Mage",
+    "original_finding": "summarize 方法中使用 spawnSync 執行指令，未處理退出訊號可能導致清理競態。",
+    "reason": "spawnSync 為同步阻塞呼叫，回傳後才執行 finally 清理，無並行清理路徑，不存在競態；timeout／訊號終止時 spawnSync 仍會回傳，finally 的 rmSync 必定執行。"
+  },
+  {
+    "location": "app/lib/git.js:145",
+    "role": "Maya",
+    "original_finding": "合併衝突後未檢查是否存在殘留衝突標記；建議在 git add 後以 grep 掃描衝突標記。",
+    "reason": "createResolveBranch 刻意保留衝突標記並 commit，讓開發者在解衝突 PR 中看到並手動解決（PR body 亦明確要求解決 `<<<<<<<` 等標記），保留標記為設計核心；若在此偵測並失敗反而會破壞既定流程。"
+  },
+  {
+    "location": "app/lib/opencode.js:40",
+    "role": "Rogue",
+    "original_finding": "頻繁寫入讀取 opencode.json 設定檔造成無謂的 I/O；建議透過參數或環境變數傳入配置。",
+    "reason": "summarize 每次 action 執行僅呼叫一次，並非「頻繁」；opencode 以 OPENCODE_CONFIG 指向設定檔為其官方配置介面，寫入單一小檔的 I/O 可忽略。"
+  },
+  {
+    "location": "app/index.js:80",
+    "role": "Bard",
+    "original_finding": "分支命名格式若目標分支名稱過長，可能導致總長度超過 Git 限制；建議確保不超過 255 字元。",
+    "reason": "buildResolveBranchName 已將主體截斷至 MAX_BRANCH_STEM_LENGTH（180），連同前綴 `resolve-conflict/`（17）與 runId 後綴，總長度約 207，遠低於 Git 的 255 上限，已滿足建議。"
+  },
+  {
+    "location": "app/index.js:52",
+    "role": "Mage",
+    "original_finding": "opencode 失敗時，若相關資訊皆為空，fallback 機制產出的 PR 描述將空洞無效；建議檢查輸出內容或拋錯。",
+    "reason": "fallbackSummary 的 title 在無 commit 時退回 `Merge <source> into <target>`，description 恆包含固定結構標題（## 變更摘要、### Commits、### 變更檔案）與 `(無)` 佔位，不會產生空字串；PR 仍具基本可讀內容，非缺陷。"
+  },
+  {
+    "location": "app/lib/util.js:11, 13",
+    "role": "Bard",
+    "original_finding": "run 函式 Buffer 大小硬編碼，缺乏靈活性，且針對極端巨大輸入缺乏保護。",
+    "reason": "maxBuffer（64MB）為刻意的上限保護而非預先配置；本 action 於即拋容器內執行，將其抽為環境變數只增配置面而無實益。等同已收錄的 util.js:14 排除（同一機制）。"
+  },
+  {
+    "location": "app/index.js:176",
+    "role": "Bard",
+    "original_finding": "PR 已存在時僅記錄 log.info，CI 流程中可能需要更明確的提示；建議改用 log.warn 或 log.notice。",
+    "reason": "「PR 已存在」是冪等重跑下的正常且預期結果，log.info 語意正確；改為 warn 會在正常流程中產生誤導性警告雜訊，屬偏好而非缺陷。"
+  },
+  {
+    "location": "app/lib/git.js:32",
+    "role": "Leo",
+    "original_finding": "Sensitive Token 處理耦合在 Git 類別中，且未驗證有效性；建議將遮蔽邏輯交由 util.js 或於初始化時驗證。",
+    "reason": "token 遮蔽邏輯已實作於 util.js 的 maskSecrets 並由 Git 類別重用（非重複實作）；token 存在性已於 inputs.js 的 required('GITEA_TOKEN') 驗證。Git 持有 token 以組 http.extraheader 為必要，耦合度可接受。"
+  },
+  {
+    "location": "app/lib/git.js:17, 37",
+    "role": "Mage/Assassin",
+    "original_finding": "Git 命令列以 -c http.extraheader 傳遞敏感 Token（竊取風險），並使用全域 git config（污染環境/權限衝突）。",
+    "reason": "token 經 `-c http.extraheader` 帶入雖會出現在 git 的 argv，但本 action 於單租戶、即拋的 CI 容器內執行，無其他使用者可讀 /proc，與已收錄的 gitea.js:28 同一信任模型。safe.directory 基於安全考量 git 刻意忽略 repo-local 設定，必須寫在 global（見已收錄的 git.js:39,52 排除），容器即拋無污染。detectConflict 的測試已於 app/lib/git.test.js 補上（整合測試）。"
+  },
+  {
+    "location": "app/lib/git.js:148, 84",
+    "role": "Leo/Rogue",
+    "original_finding": "Git 提交策略不精確（git add -A 可能帶入非預期變更），且頻繁執行完整 checkout/merge 造成高 I/O；建議改用 merge-tree。",
+    "reason": "createResolveBranch 的 `git add -A` 為刻意保留完整合併結果（含衝突標記）供人工於 PR 解決，已有整合測試（app/lib/git.test.js）驗證行為；於即拋容器、單次執行下，checkout/merge 的 I/O 成本可忽略，改用 merge-tree 屬選用最佳化而非缺陷，現行 detectConflict 行為正確且已測。"
+  }
+]
diff --git a/.gitea/ai-review/findings.json b/.gitea/ai-review/findings.json
new file mode 100644
index 0000000..fe51488
--- /dev/null
+++ b/.gitea/ai-review/findings.json
@@ -0,0 +1 @@
+[]
diff --git a/.gitea/workflows/cd.yaml b/.gitea/workflows/cd.yaml
new file mode 100644
index 0000000..30b1952
--- /dev/null
+++ b/.gitea/workflows/cd.yaml
@@ -0,0 +1,12 @@
+name: CD
+on:
+  push:
+    branches:
+    - master
+jobs:
+  release-tag-version:
+    name: Release Tag Version
+    runs-on: ubuntu
+    steps:
+    - name: 釋出並標註成品版本
+      uses: https://gitea.jsc.idv.tw/composite-actions/release-tag-version@${{ vars.ACTION_RELEASE_TAG_VERSION }}
diff --git a/.gitea/workflows/ci.yaml b/.gitea/workflows/ci.yaml
new file mode 100644
index 0000000..4177dfd
--- /dev/null
+++ b/.gitea/workflows/ci.yaml
@@ -0,0 +1,30 @@
+name: CI
+on:
+  pull_request:
+    branches-ignore:
+    - master
+    types: [opened, synchronize]
+jobs:
+  test:
+    name: Unit Test
+    runs-on: ubuntu
+    steps:
+    - uses: actions/checkout@v4
+    - uses: actions/setup-node@v4
+      with:
+        node-version: '20'
+    - name: 執行單元測試
+      run: node --test
+      working-directory: app
+  ai-code-review:
+    name: AI Code Review
+    runs-on: ubuntu
+    permissions:
+      contents: write
+      pull-requests: write
+      issues: write
+    steps:
+    - name: AI 程式碼審查 by OpenCode
+      uses: https://gitea.jsc.idv.tw/composite-actions/opencode-code-review@${{ vars.ACTION_OPENCODE_CODE_REVIEW_VERSION }}
+      with:
+        token: ${{ secrets.TOKEN }}
diff --git a/Dockerfile b/Dockerfile
index af3dacb..dfa0d9e 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,10 +1,22 @@
-FROM alpine:latest
+FROM node:20-bookworm-slim
+
+# 安裝必要工具：git（操作分支/合併）、bash、ca-certificates、curl（安裝 opencode）
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends git bash ca-certificates curl \
+    && rm -rf /var/lib/apt/lists/*
+
+# 安裝 opencode CLI（用於分析 git diff 產生 PR 標題與描述）
+# 釘住版本以確保建置可重現並降低供應鏈風險
+RUN npm install -g opencode-ai@1.17.11
+
+# 複製 Node.js 應用程式
+COPY app/ /app/
+WORKDIR /app
+
+# 應用程式無第三方相依套件，僅在有 package-lock 時安裝
+RUN if [ -f package-lock.json ]; then npm ci --omit=dev; fi
 
-# 安裝必要的工具
-RUN apk add --no-cache --no-check-certificate bash
-    
 COPY entrypoint.sh /entrypoint.sh
-
 RUN chmod +x /entrypoint.sh
 
-ENTRYPOINT ["/entrypoint.sh"]
\ No newline at end of file
+ENTRYPOINT ["/entrypoint.sh"]
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..ade622e
--- /dev/null
+++ b/README.md
@@ -0,0 +1,74 @@
+# AI Pull Request
+
+Gitea Docker Action：使用 [opencode](https://opencode.ai) 分析 `git diff`，自動產生 Pull Request 的標題與描述，並透過 Gitea token 建立 PR。
+
+## 功能
+
+1. 抓取**來源分支**與**目標分支**，計算兩者的差異（commits / stat / diff）。
+2. 呼叫 `opencode`（指定 `base_url` / `model` / `provider`）將 diff 總結成 PR 標題與描述（固定使用繁體中文）。
+   - 若 opencode 不可用或解析失敗，會自動以 commit 訊息與檔案統計產生 fallback 標題/描述。
+3. 偵測來源分支合併進目標分支是否會**衝突**：
+   - **無衝突**：直接建立 `來源分支 → 目標分支` 的 PR。
+   - **有衝突**：從**目標分支**建立解衝突分支，合併來源分支（保留衝突標記後 commit 並推送），再建立 `解衝突分支 → 來源分支` 的 PR，讓開發者在 PR 中手動解衝突；解決後來源分支即可順利合併回目標分支。
+
+## 輸入參數（inputs）
+
+| 參數 | 必填 | 說明 |
+| --- | --- | --- |
+| `source_branch` | ✅ | 來源分支 |
+| `target_branch` | ✅ | 目標分支 |
+| `opencode_base_url` | ✅ | opencode 使用的模型服務 base URL（OpenAI 相容端點） |
+| `opencode_model` | ✅ | opencode 使用的模型名稱 |
+| `opencode_provider` | ✅ | opencode provider 名稱 |
+
+## 使用範例
+
+```yaml
+name: AI PR
+on:
+  workflow_dispatch:
+    inputs:
+      source_branch:
+        description: '來源分支'
+        required: true
+      target_branch:
+        description: '目標分支'
+        required: true
+
+jobs:
+  ai-pull-request:
+    runs-on: ubuntu
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: AI Pull Request
+        uses: https://gitea.jsc.idv.tw/docker-actions/ai-pull-request@v1
+        with:
+          source_branch: ${{ inputs.source_branch }}
+          target_branch: ${{ inputs.target_branch }}
+          opencode_base_url: ${{ vars.OPENCODE_BASE_URL }}
+          opencode_model: ${{ vars.OPENCODE_MODEL }}
+          opencode_provider: ${{ vars.OPENCODE_PROVIDER }}
+```
+
+## 開發
+
+應用程式以 Node.js 開發，位於 [`app/`](app/)，進入點為 [`entrypoint.sh`](entrypoint.sh) → `node /app/index.js`。
+
+```
+app/
+├── index.js          # 主流程
+└── lib/
+    ├── inputs.js      # 讀取/驗證環境變數
+    ├── git.js         # git 操作（fetch / diff / 衝突偵測 / 解衝突分支）
+    ├── gitea.js       # Gitea API（建立 PR）
+    ├── opencode.js    # 呼叫 opencode 產生標題與描述
+    └── util.js        # 共用工具（執行指令、日誌、遮蔽敏感資訊）
+```
+
+語法檢查：
+
+```bash
+cd app && node --check index.js
+```
diff --git a/action.yaml b/action.yaml
index 2000f7c..5970182 100644
--- a/action.yaml
+++ b/action.yaml
@@ -1,22 +1,31 @@
-name: 'Docker Action Template'
-description: 'Docker Action 範本'
+name: 'AI Pull Request'
+description: '使用 opencode 分析 git diff 產生 PR 標題與描述，並透過 Gitea token 建立 Pull Request；遇衝突時自動建立解衝突分支'
 author: 'Jeffery'
 inputs:
-  gitea_token:
-    description: 'Gitea Token'
+  source_branch:
+    description: '來源分支'
+    required: true
+  target_branch:
+    description: '目標分支'
+    required: true
+  opencode_base_url:
+    description: 'opencode 使用的模型服務 base URL（OpenAI 相容端點）'
+    required: true
+  opencode_model:
+    description: 'opencode 使用的模型名稱'
+    required: true
+  opencode_provider:
+    description: 'opencode provider 名稱'
     required: true
-  text:
-    description: '輸入的文字'
-    required: false
-    default: 'Hello, World!'
-outputs:
-  text:
-    description: '輸出的文字'
 runs:
   using: 'docker'
   image: 'Dockerfile'
   env:
     GITEA_SERVER_URL: ${{ gitea.server_url }}
     GITEA_REPOSITORY: ${{ gitea.repository }}
-    GITEA_TOKEN: ${{ secrets.GITEA_TOKEN || inputs.gitea_token }}
-    TEXT: ${{ inputs.text }}
\ No newline at end of file
+    GITEA_TOKEN: ${{ gitea.token }}
+    SOURCE_BRANCH: ${{ inputs.source_branch }}
+    TARGET_BRANCH: ${{ inputs.target_branch }}
+    OPENCODE_BASE_URL: ${{ inputs.opencode_base_url }}
+    OPENCODE_MODEL: ${{ inputs.opencode_model }}
+    OPENCODE_PROVIDER: ${{ inputs.opencode_provider }}
diff --git a/app/index.js b/app/index.js
new file mode 100644
index 0000000..227b12f
--- /dev/null
+++ b/app/index.js
@@ -0,0 +1,206 @@
+import { fileURLToPath } from 'node:url';
+import { loadInputs, logInputs } from './lib/inputs.js';
+import { Git } from './lib/git.js';
+import { GiteaClient } from './lib/gitea.js';
+import { OpenCode } from './lib/opencode.js';
+import { log, maskSecrets } from './lib/util.js';
+
+async function main() {
+  const inputs = loadInputs();
+  logInputs(inputs);
+
+  const remoteUrl = `${inputs.serverUrl}/${inputs.owner}/${inputs.repo}.git`;
+
+  const git = new Git({ cwd: inputs.workspace, remoteUrl, token: inputs.token });
+  const gitea = new GiteaClient({
+    serverUrl: inputs.serverUrl,
+    owner: inputs.owner,
+    repo: inputs.repo,
+    token: inputs.token,
+  });
+  const opencode = new OpenCode({ ...inputs.opencode, language: inputs.language });
+
+  // 1. 準備 git 環境並抓取兩個分支
+  log.step('準備 git 環境');
+  git.configure();
+  git.fetchBranches([inputs.sourceBranch, inputs.targetBranch]);
+
+  // 2. 確認來源分支相對目標分支有變更
+  const ahead = git.countAheadCommits(inputs.targetBranch, inputs.sourceBranch);
+  if (ahead === 0) {
+    log.warn(`來源分支 ${inputs.sourceBranch} 相對 ${inputs.targetBranch} 沒有新的 commit，無需建立 PR`);
+    return;
+  }
+  log.info(`來源分支領先 ${ahead} 個 commit`);
+
+  // 3. 蒐集 diff 內容
+  log.step('蒐集 git diff');
+  const commitMessages = git.getCommitMessages(inputs.targetBranch, inputs.sourceBranch);
+  const diffStat = git.getDiffStat(inputs.targetBranch, inputs.sourceBranch);
+  const fullDiff = git.getDiff(inputs.targetBranch, inputs.sourceBranch);
+  const { diff, truncated } = truncateDiff(fullDiff, inputs.maxDiffChars);
+  if (truncated) log.warn(`diff 過大，已截斷至 ${inputs.maxDiffChars} 字元`);
+
+  // 4. 使用 opencode 產生標題與描述（失敗則 fallback）
+  log.step('使用 opencode 產生 PR 標題與描述');
+  let summary = await opencode.summarize({
+    sourceBranch: inputs.sourceBranch,
+    targetBranch: inputs.targetBranch,
+    commitMessages,
+    diffStat,
+    diff,
+  });
+  if (!summary) {
+    log.warn('改用 commit/stat 自動產生標題與描述');
+    summary = fallbackSummary({
+      source: inputs.sourceBranch,
+      target: inputs.targetBranch,
+      commitMessages,
+      diffStat,
+    });
+  }
+  log.success(`標題: ${summary.title}`);
+
+  // 5. 偵測合併衝突
+  log.step('偵測合併衝突');
+  const { hasConflict, files } = git.detectConflict(inputs.targetBranch, inputs.sourceBranch);
+
+  if (!hasConflict) {
+    // 5a. 無衝突：直接建立 來源 → 目標 的 PR
+    log.success('無衝突，建立來源分支 → 目標分支的 PR');
+    const { pull, created } = await gitea.createPull({
+      head: inputs.sourceBranch,
+      base: inputs.targetBranch,
+      title: summary.title,
+      body: summary.description,
+    });
+    reportPull(pull, created);
+    return;
+  }
+
+  // 5b. 有衝突：從目標分支建立解衝突分支，合併來源分支後 PR 回來源分支
+  log.warn(`偵測到衝突檔案 (${files.length}): ${files.join(', ')}`);
+  const resolveBranch = buildResolveBranchName(inputs.targetBranch, inputs.sourceBranch);
+
+  log.step('建立解衝突分支並合併來源分支');
+  const { files: conflictFiles } = git.createResolveBranch({
+    target: inputs.targetBranch,
+    source: inputs.sourceBranch,
+    resolveBranch,
+  });
+
+  const body = buildResolveBody({
+    source: inputs.sourceBranch,
+    target: inputs.targetBranch,
+    resolveBranch,
+    files: conflictFiles.length ? conflictFiles : files,
+    summary,
+  });
+
+  log.step('建立解衝突分支 → 來源分支的 PR');
+  const { pull, created } = await gitea.createPull({
+    head: resolveBranch,
+    base: inputs.sourceBranch,
+    title: `解衝突: 將 ${inputs.targetBranch} 合併回 ${inputs.sourceBranch}`,
+    body,
+  });
+  reportPull(pull, created);
+}
+
+/** 把 diff 截斷至上限字元數。 */
+function truncateDiff(diff, maxChars) {
+  if (!diff || diff.length <= maxChars) return { diff: diff || '', truncated: false };
+  return {
+    diff: `${diff.slice(0, maxChars)}\n\n... (diff 已截斷，僅顯示前 ${maxChars} 字元) ...`,
+    truncated: true,
+  };
+}
+
+/** opencode 不可用時，用 commit 訊息與 stat 產生簡單摘要。 */
+function fallbackSummary({ source, target, commitMessages, diffStat }) {
+  const firstCommit = (commitMessages || '')
+    .split('\n')
+    .map((l) => l.replace(/^- /, '').trim())
+    .find(Boolean);
+  const title = firstCommit || `Merge ${source} into ${target}`;
+  const description = [
+    `## 變更摘要`,
+    ``,
+    `將 \`${source}\` 合併到 \`${target}\`。`,
+    ``,
+    `### Commits`,
+    commitMessages || '(無)',
+    ``,
+    `### 變更檔案`,
+    '```',
+    diffStat || '(無)',
+    '```',
+  ].join('\n');
+  return { title, description };
+}
+
+// 解衝突分支主體最大長度；連同前綴 `resolve-conflict/` 與 runId 後綴，
+// 總長度仍遠低於 Git 對 ref 名稱的限制（約 255）。
+const MAX_BRANCH_STEM_LENGTH = 180;
+
+/** 解衝突分支名稱。 */
+function buildResolveBranchName(target, source) {
+  const runId = process.env.GITHUB_RUN_NUMBER || process.env.GITHUB_RUN_ID || '';
+  const safe = (s) => s.replace(/[^a-zA-Z0-9._/-]/g, '-');
+  const suffix = runId ? `-${runId}` : '';
+  // 截斷主體長度，避免 target/source 過長使分支名稱超出 Git 限制
+  const stem = `${safe(target)}-into-${safe(source)}`.slice(0, MAX_BRANCH_STEM_LENGTH);
+  return `resolve-conflict/${stem}${suffix}`;
+}
+
+/** 解衝突 PR 的描述。 */
+function buildResolveBody({ source, target, resolveBranch, files, summary }) {
+  return [
+    `## ⚠️ 自動解衝突 PR`,
+    ``,
+    `來源分支 \`${source}\` 合併到目標分支 \`${target}\` 時偵測到衝突，`,
+    `已自動從 \`${target}\` 建立解衝突分支 \`${resolveBranch}\` 並合併 \`${source}\`。`,
+    ``,
+    `**此 PR 會將 \`${resolveBranch}\` 合併回 \`${source}\`，請在合併前手動解決下列檔案的衝突標記（\`<<<<<<<\`、\`=======\`、\`>>>>>>>\`）：**`,
+    ``,
+    ...files.map((f) => `- \`${f}\``),
+    ``,
+    `### ✅ 合併前人工檢查清單`,
+    ``,
+    `- [ ] 已移除所有檔案中的衝突標記（\`<<<<<<<\`、\`=======\`、\`>>>>>>>\`）`,
+    `- [ ] 已確認合併結果可正常建置／執行`,
+    `- [ ] 已保留雙方必要變更，無誤刪`,
+    ``,
+    `解決並合併此 PR 後，\`${source}\` 即可順利合併進 \`${target}\`。`,
+    ``,
+    `---`,
+    ``,
+    `### AI 變更摘要`,
+    ``,
+    summary.description || '(無)',
+  ].join('\n');
+}
+
+/** 印出 PR 結果。 */
+function reportPull(pull, created) {
+  const url = pull?.html_url || pull?.url || '';
+  const number = pull?.number || '';
+  if (created) {
+    log.success(`已建立 PR #${number}: ${url}`);
+  } else {
+    log.info(`PR 已存在 #${number}: ${url}`);
+  }
+}
+
+// 純函式對外匯出，供測試使用（不觸發 main 流程）
+export { truncateDiff, fallbackSummary, buildResolveBranchName, buildResolveBody };
+
+// 僅在直接以 `node index.js` 執行時才跑主流程；被測試 import 時不執行
+if (process.argv[1] && fileURLToPath(import.meta.url) === process.argv[1]) {
+  main().catch((err) => {
+    const detail = err?.stack || err?.message || String(err);
+    // 錯誤訊息／stack 可能夾帶 token，輸出到 CI 日誌前先遮蔽
+    log.error(maskSecrets(detail, [process.env.GITEA_TOKEN]));
+    process.exit(1);
+  });
+}
diff --git a/app/index.test.js b/app/index.test.js
new file mode 100644
index 0000000..e609483
--- /dev/null
+++ b/app/index.test.js
@@ -0,0 +1,79 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  truncateDiff,
+  fallbackSummary,
+  buildResolveBranchName,
+  buildResolveBody,
+} from './index.js';
+
+test('truncateDiff: 內容在上限內不截斷', () => {
+  const { diff, truncated } = truncateDiff('abc', 100);
+  assert.equal(diff, 'abc');
+  assert.equal(truncated, false);
+});
+
+test('truncateDiff: null/空字串回傳空字串且不截斷', () => {
+  assert.deepEqual(truncateDiff(null, 100), { diff: '', truncated: false });
+  assert.deepEqual(truncateDiff('', 100), { diff: '', truncated: false });
+});
+
+test('truncateDiff: 超過上限時截斷並標示', () => {
+  const big = 'x'.repeat(50);
+  const { diff, truncated } = truncateDiff(big, 10);
+  assert.equal(truncated, true);
+  assert.ok(diff.startsWith('xxxxxxxxxx'));
+  assert.ok(diff.includes('已截斷'));
+});
+
+test('fallbackSummary: 取首個 commit 當標題', () => {
+  const s = fallbackSummary({
+    source: 'feature',
+    target: 'develop',
+    commitMessages: '- feat: 新增功能\n- fix: 修正',
+    diffStat: ' a.js | 2 +-',
+  });
+  assert.equal(s.title, 'feat: 新增功能');
+  assert.ok(s.description.includes('## 變更摘要'));
+  assert.ok(s.description.includes('a.js'));
+});
+
+test('fallbackSummary: 無 commit 時退回 Merge 標題且描述非空', () => {
+  const s = fallbackSummary({
+    source: 'feature',
+    target: 'develop',
+    commitMessages: '',
+    diffStat: '',
+  });
+  assert.equal(s.title, 'Merge feature into develop');
+  assert.ok(s.description.includes('(無)'));
+  assert.ok(s.description.length > 0);
+});
+
+test('buildResolveBranchName: 含前綴並淨化非法字元', () => {
+  const name = buildResolveBranchName('develop', 'feature/x y');
+  assert.ok(name.startsWith('resolve-conflict/'));
+  assert.ok(name.includes('-into-'));
+  // 空白等非法字元被替換為 -
+  assert.ok(!/\s/.test(name));
+});
+
+test('buildResolveBranchName: 過長 target/source 仍遠低於 255', () => {
+  const long = 'a'.repeat(500);
+  const name = buildResolveBranchName(long, long);
+  assert.ok(name.length < 255);
+});
+
+test('buildResolveBody: 含衝突檔案清單與人工檢查清單', () => {
+  const body = buildResolveBody({
+    source: 'feature',
+    target: 'develop',
+    resolveBranch: 'resolve-conflict/develop-into-feature',
+    files: ['a.js', 'b.js'],
+    summary: { title: 't', description: '摘要內容' },
+  });
+  assert.ok(body.includes('- `a.js`'));
+  assert.ok(body.includes('- `b.js`'));
+  assert.ok(body.includes('合併前人工檢查清單'));
+  assert.ok(body.includes('摘要內容'));
+});
diff --git a/app/lib/git.js b/app/lib/git.js
new file mode 100644
index 0000000..eb6c880
--- /dev/null
+++ b/app/lib/git.js
@@ -0,0 +1,166 @@
+import { run, runOrThrow, log, maskSecrets } from './util.js';
+
+/**
+ * 封裝這個 action 需要的 git 操作。所有對遠端的操作都透過
+ * http.extraheader 帶上 Gitea token，避免 token 寫進 remote URL。
+ */
+export class Git {
+  /**
+   * @param {object} opts
+   * @param {string} opts.cwd 工作目錄（已 checkout 的 repo）
+   * @param {string} opts.remoteUrl 不含認證資訊的 repo HTTPS URL
+   * @param {string} opts.token Gitea token
+   */
+  constructor({ cwd, remoteUrl, token }) {
+    this.cwd = cwd;
+    this.remoteUrl = remoteUrl;
+    this.token = token;
+    // Gitea 接受 "Authorization: token <token>"
+    this.authArgs = ['-c', `http.extraheader=Authorization: token ${token}`];
+  }
+
+  /** 帶 token 的 git 執行（用於遠端操作），不會把 args 印進日誌。 */
+  _authGit(args, { throwOnError = true } = {}) {
+    const full = [...this.authArgs, ...args];
+    const result = run('git', full, { cwd: this.cwd });
+    if (throwOnError && result.status !== 0) {
+      const detail = maskSecrets(result.stderr || result.stdout, [this.token]).trim();
+      throw new Error(`git ${args.join(' ')} 失敗 (${result.status}):\n${detail}`);
+    }
+    return result;
+  }
+
+  /** 不帶 token 的本地 git 執行。 */
+  _git(args, opts = {}) {
+    return run('git', args, { cwd: this.cwd, ...opts });
+  }
+
+  /** 初始化必要的 git 設定（safe.directory、user.name/email）。 */
+  configure() {
+    run('git', ['config', '--global', '--add', 'safe.directory', this.cwd]);
+    run('git', ['config', '--global', '--add', 'safe.directory', '*']);
+    // 解衝突分支需要建立 merge commit，必須有身份
+    this._git(['config', 'user.name', process.env.GIT_AUTHOR_NAME || 'ai-pull-request[bot]']);
+    this._git(['config', 'user.email', process.env.GIT_AUTHOR_EMAIL || 'ai-pull-request@users.noreply.gitea']);
+  }
+
+  /**
+   * 從遠端抓取 source 與 target 分支到本地追蹤分支 refs/remotes/pr/<branch>。
+   *
+   * @param {string[]} branches
+   */
+  fetchBranches(branches) {
+    const refspecs = branches.map((b) => `+refs/heads/${b}:refs/remotes/pr/${b}`);
+    log.info(`抓取分支: ${branches.join(', ')}`);
+    this._authGit(['fetch', '--no-tags', this.remoteUrl, ...refspecs]);
+  }
+
+  /** 取得分支的 commit 數量差異（source 比 target 多幾個 commit）。 */
+  countAheadCommits(target, source) {
+    const result = this._git(['rev-list', '--count', `refs/remotes/pr/${target}..refs/remotes/pr/${source}`]);
+    return result.status === 0 ? parseInt(result.stdout.trim(), 10) || 0 : 0;
+  }
+
+  /** 取得 source 相對 target 的 commit 訊息清單。 */
+  getCommitMessages(target, source, limit = 50) {
+    const result = this._git([
+      'log',
+      `--max-count=${limit}`,
+      '--pretty=format:- %s',
+      `refs/remotes/pr/${target}..refs/remotes/pr/${source}`,
+    ]);
+    return result.status === 0 ? result.stdout.trim() : '';
+  }
+
+  /** 取得 diff 統計（--stat）。 */
+  getDiffStat(target, source) {
+    const result = this._git([
+      'diff',
+      '--stat',
+      `refs/remotes/pr/${target}...refs/remotes/pr/${source}`,
+    ]);
+    return result.status === 0 ? result.stdout.trim() : '';
+  }
+
+  /** 取得完整 diff（three-dot，等同 PR 在 merge base 之後的變更）。 */
+  getDiff(target, source) {
+    const result = this._git([
+      'diff',
+      `refs/remotes/pr/${target}...refs/remotes/pr/${source}`,
+    ]);
+    return result.status === 0 ? result.stdout : '';
+  }
+
+  /**
+   * 偵測 source 合併進 target 是否會衝突（不會留下任何變更）。
+   *
+   * @returns {{ hasConflict: boolean, files: string[] }}
+   */
+  detectConflict(target, source) {
+    // 建立暫時的本地 target 分支，嘗試以 --no-commit 合併 source。
+    // 名稱帶 PID，避免並行或前次殘留造成命名衝突。
+    const tmp = `__conflict_check_${target}_${process.pid}`;
+    this._git(['checkout', '-B', tmp, `refs/remotes/pr/${target}`]);
+
+    try {
+      const merge = this._git(['merge', '--no-commit', '--no-ff', `refs/remotes/pr/${source}`]);
+      const hasConflict = merge.status !== 0;
+      let files = [];
+
+      if (hasConflict) {
+        const unmerged = this._git(['diff', '--name-only', '--diff-filter=U']);
+        files = unmerged.stdout.split('\n').map((s) => s.trim()).filter(Boolean);
+      }
+
+      return { hasConflict, files };
+    } finally {
+      // 無論成敗都還原工作區並清除暫存分支
+      this._git(['merge', '--abort']);
+      this._git(['checkout', '--detach']);
+      this._git(['branch', '-D', tmp]);
+    }
+  }
+
+  /**
+   * 建立解衝突分支：以 target 為基礎，合併 source（保留衝突標記後 commit），
+   * 再推送到遠端。
+   *
+   * @param {object} opts
+   * @param {string} opts.target 目標分支
+   * @param {string} opts.source 來源分支
+   * @param {string} opts.resolveBranch 解衝突分支名稱
+   * @returns {{ files: string[] }} 衝突檔案清單
+   */
+  createResolveBranch({ target, source, resolveBranch }) {
+    log.info(`以 ${target} 為基礎建立解衝突分支 ${resolveBranch}`);
+    this._git(['checkout', '-B', resolveBranch, `refs/remotes/pr/${target}`]);
+
+    const merge = this._git([
+      'merge',
+      '--no-ff',
+      '-m',
+      `Merge branch '${source}' into ${resolveBranch} (待人工解衝突)`,
+      `refs/remotes/pr/${source}`,
+    ]);
+
+    let files = [];
+    if (merge.status !== 0) {
+      // 合併產生衝突：將含有衝突標記的檔案標記為已解決後 commit，
+      // 讓開發者可以在 PR 中看到並解決衝突。
+      const unmerged = this._git(['diff', '--name-only', '--diff-filter=U']);
+      files = unmerged.stdout.split('\n').map((s) => s.trim()).filter(Boolean);
+
+      runOrThrow('git', ['add', '-A'], { cwd: this.cwd });
+      runOrThrow(
+        'git',
+        ['commit', '--no-verify', '-m', `Merge branch '${source}' into ${resolveBranch}（含衝突標記，待人工解衝突）`],
+        { cwd: this.cwd },
+      );
+    }
+
+    log.info(`推送解衝突分支 ${resolveBranch}`);
+    this._authGit(['push', '--force', this.remoteUrl, `HEAD:refs/heads/${resolveBranch}`]);
+
+    return { files };
+  }
+}
diff --git a/app/lib/git.test.js b/app/lib/git.test.js
new file mode 100644
index 0000000..4b5e127
--- /dev/null
+++ b/app/lib/git.test.js
@@ -0,0 +1,114 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { mkdtempSync, writeFileSync, rmSync, readFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { execFileSync } from 'node:child_process';
+import { Git } from './git.js';
+
+function g(cwd, args) {
+  return execFileSync('git', args, { cwd, encoding: 'utf8' });
+}
+
+/** 建立 bare remote + working clone，於 target/source 製造會衝突的變更。 */
+function setupRepo() {
+  const root = mkdtempSync(join(tmpdir(), 'git-test-'));
+  const bare = join(root, 'remote.git');
+  const work = join(root, 'work');
+  execFileSync('git', ['init', '-q', '--bare', bare]);
+  execFileSync('git', ['clone', '-q', bare, work]);
+  g(work, ['config', 'user.email', 'test@example.com']);
+  g(work, ['config', 'user.name', 'tester']);
+  g(work, ['config', 'commit.gpgsign', 'false']);
+
+  writeFileSync(join(work, 'file.txt'), 'base\n');
+  g(work, ['add', '-A']);
+  g(work, ['commit', '-q', '-m', 'base']);
+  const def = g(work, ['rev-parse', '--abbrev-ref', 'HEAD']).trim();
+
+  g(work, ['checkout', '-q', '-b', 'target']);
+  writeFileSync(join(work, 'file.txt'), 'target change\n');
+  g(work, ['commit', '-qam', 'target change']);
+
+  g(work, ['checkout', '-q', def]);
+  g(work, ['checkout', '-q', '-b', 'source']);
+  writeFileSync(join(work, 'file.txt'), 'source change\n');
+  g(work, ['commit', '-qam', 'source change']);
+
+  g(work, ['push', '-q', 'origin', 'target', 'source', def]);
+  return { root, bare, work };
+}
+
+test('detectConflict: 偵測到衝突並回傳衝突檔，事後還原暫存分支', () => {
+  const { root, bare, work } = setupRepo();
+  try {
+    const git = new Git({ cwd: work, remoteUrl: bare, token: 'x' });
+    git.configure();
+    git.fetchBranches(['target', 'source']);
+
+    assert.ok(git.countAheadCommits('target', 'source') >= 1);
+
+    const det = git.detectConflict('target', 'source');
+    assert.equal(det.hasConflict, true);
+    assert.ok(det.files.includes('file.txt'));
+
+    // 暫存分支應已清除
+    assert.ok(!g(work, ['branch']).includes('__conflict_check'));
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});
+
+test('createResolveBranch: 推送含衝突標記的解衝突分支到 remote', () => {
+  const { root, bare, work } = setupRepo();
+  try {
+    const git = new Git({ cwd: work, remoteUrl: bare, token: 'x' });
+    git.configure();
+    git.fetchBranches(['target', 'source']);
+
+    const res = git.createResolveBranch({ target: 'target', source: 'source', resolveBranch: 'resolve-x' });
+    assert.ok(res.files.includes('file.txt'));
+
+    // remote 應有 resolve-x 分支
+    assert.ok(execFileSync('git', ['--git-dir', bare, 'branch'], { encoding: 'utf8' }).includes('resolve-x'));
+    // 已 commit 的檔案應保留衝突標記
+    assert.ok(readFileSync(join(work, 'file.txt'), 'utf8').includes('<<<<<<<'));
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});
+
+test('detectConflict: 可順利合併時回報無衝突', () => {
+  const root = mkdtempSync(join(tmpdir(), 'git-test-'));
+  try {
+    const bare = join(root, 'remote.git');
+    const work = join(root, 'work');
+    execFileSync('git', ['init', '-q', '--bare', bare]);
+    execFileSync('git', ['clone', '-q', bare, work]);
+    g(work, ['config', 'user.email', 'test@example.com']);
+    g(work, ['config', 'user.name', 'tester']);
+    g(work, ['config', 'commit.gpgsign', 'false']);
+
+    writeFileSync(join(work, 'a.txt'), 'base\n');
+    g(work, ['add', '-A']);
+    g(work, ['commit', '-qm', 'base']);
+    const def = g(work, ['rev-parse', '--abbrev-ref', 'HEAD']).trim();
+
+    g(work, ['checkout', '-q', '-b', 'target']); // target 不動
+    g(work, ['checkout', '-q', def]);
+    g(work, ['checkout', '-q', '-b', 'source']);
+    writeFileSync(join(work, 'b.txt'), 'new file\n'); // 改不同檔，無衝突
+    g(work, ['add', '-A']);
+    g(work, ['commit', '-qm', 'add b']);
+    g(work, ['push', '-q', 'origin', 'target', 'source', def]);
+
+    const git = new Git({ cwd: work, remoteUrl: bare, token: 'x' });
+    git.configure();
+    git.fetchBranches(['target', 'source']);
+    const det = git.detectConflict('target', 'source');
+    assert.equal(det.hasConflict, false);
+    assert.deepEqual(det.files, []);
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});
diff --git a/app/lib/gitea.js b/app/lib/gitea.js
new file mode 100644
index 0000000..28ff34e
--- /dev/null
+++ b/app/lib/gitea.js
@@ -0,0 +1,98 @@
+import { log } from './util.js';
+
+/**
+ * 極簡的 Gitea API client，只實作這個 action 需要的 PR 相關操作。
+ */
+export class GiteaClient {
+  /**
+   * @param {object} opts
+   * @param {string} opts.serverUrl Gitea base URL（不含結尾斜線）
+   * @param {string} opts.owner
+   * @param {string} opts.repo
+   * @param {string} opts.token
+   */
+  constructor({ serverUrl, owner, repo, token }) {
+    this.apiBase = `${serverUrl}/api/v1`;
+    this.owner = owner;
+    this.repo = repo;
+    this.token = token;
+  }
+
+  async _request(method, path, body) {
+    const url = `${this.apiBase}${path}`;
+    const res = await fetch(url, {
+      method,
+      headers: {
+        Authorization: `token ${this.token}`,
+        'Content-Type': 'application/json',
+        Accept: 'application/json',
+      },
+      body: body ? JSON.stringify(body) : undefined,
+    });
+
+    const text = await res.text();
+    let json;
+    try {
+      json = text ? JSON.parse(text) : {};
+    } catch {
+      json = { message: text };
+    }
+    return { ok: res.ok, status: res.status, json };
+  }
+
+  /**
+   * 查詢 head -> base 是否已存在開啟中的 PR。
+   *
+   * @param {string} head 來源分支
+   * @param {string} base 目標分支
+   * @returns {Promise<object|null>}
+   */
+  async findOpenPull(head, base) {
+    // Gitea pulls 不直接支援 head/base 過濾，這裡撈開啟中的 PR 自行比對
+    const { ok, json } = await this._request(
+      'GET',
+      `/repos/${this.owner}/${this.repo}/pulls?state=open&limit=50`,
+    );
+    if (!ok || !Array.isArray(json)) return null;
+    return (
+      json.find(
+        (pr) => pr?.head?.ref === head && pr?.base?.ref === base,
+      ) || null
+    );
+  }
+
+  /**
+   * 建立 Pull Request。若已存在相同 head/base 的 PR 則回傳既有 PR。
+   *
+   * @param {object} opts
+   * @param {string} opts.head 來源分支
+   * @param {string} opts.base 目標分支
+   * @param {string} opts.title
+   * @param {string} opts.body
+   * @returns {Promise<{ pull: object, created: boolean }>}
+   */
+  async createPull({ head, base, title, body }) {
+    log.info(`建立 PR: ${head} → ${base}`);
+    const { ok, status, json } = await this._request(
+      'POST',
+      `/repos/${this.owner}/${this.repo}/pulls`,
+      { head, base, title, body },
+    );
+
+    if (ok) {
+      return { pull: json, created: true };
+    }
+
+    // 422 通常代表 PR 已存在
+    if (status === 422 || status === 409) {
+      const existing = await this.findOpenPull(head, base);
+      if (existing) {
+        log.warn(`PR 已存在: #${existing.number}`);
+        return { pull: existing, created: false };
+      }
+    }
+
+    const message = json?.message || JSON.stringify(json);
+    throw new Error(`建立 PR 失敗 (${status}): ${message}`);
+  }
+}
diff --git a/app/lib/gitea.test.js b/app/lib/gitea.test.js
new file mode 100644
index 0000000..9823e76
--- /dev/null
+++ b/app/lib/gitea.test.js
@@ -0,0 +1,78 @@
+import { test, afterEach } from 'node:test';
+import assert from 'node:assert/strict';
+import { GiteaClient } from './gitea.js';
+
+const realFetch = globalThis.fetch;
+afterEach(() => { globalThis.fetch = realFetch; });
+
+function makeClient() {
+  return new GiteaClient({
+    serverUrl: 'https://gitea.example',
+    owner: 'o',
+    repo: 'r',
+    token: 't',
+  });
+}
+
+/** 建立假的 fetch，依序回傳給定的回應。 */
+function stubFetch(responses) {
+  const calls = [];
+  globalThis.fetch = async (url, opts) => {
+    calls.push({ url, opts });
+    const r = responses.shift();
+    return {
+      ok: r.status >= 200 && r.status < 300,
+      status: r.status,
+      text: async () => (r.body == null ? '' : JSON.stringify(r.body)),
+    };
+  };
+  return calls;
+}
+
+test('createPull: 成功建立回傳 created=true', async () => {
+  stubFetch([{ status: 201, body: { number: 7, html_url: 'u' } }]);
+  const { pull, created } = await makeClient().createPull({
+    head: 'feature', base: 'develop', title: 't', body: 'b',
+  });
+  assert.equal(created, true);
+  assert.equal(pull.number, 7);
+});
+
+test('createPull: 422 已存在時回查既有 PR，created=false', async () => {
+  stubFetch([
+    { status: 422, body: { message: 'already exists' } },
+    { status: 200, body: [
+      { number: 3, head: { ref: 'feature' }, base: { ref: 'develop' } },
+    ] },
+  ]);
+  const { pull, created } = await makeClient().createPull({
+    head: 'feature', base: 'develop', title: 't', body: 'b',
+  });
+  assert.equal(created, false);
+  assert.equal(pull.number, 3);
+});
+
+test('createPull: 422 但查無對應 PR 時丟出錯誤', async () => {
+  stubFetch([
+    { status: 422, body: { message: 'bad' } },
+    { status: 200, body: [] },
+  ]);
+  await assert.rejects(
+    () => makeClient().createPull({ head: 'feature', base: 'develop', title: 't', body: 'b' }),
+    /建立 PR 失敗/,
+  );
+});
+
+test('createPull: 其他錯誤狀態碼直接丟出', async () => {
+  stubFetch([{ status: 500, body: { message: '伺服器錯誤' } }]);
+  await assert.rejects(
+    () => makeClient().createPull({ head: 'feature', base: 'develop', title: 't', body: 'b' }),
+    /建立 PR 失敗 \(500\)/,
+  );
+});
+
+test('findOpenPull: 非陣列回應回傳 null', async () => {
+  stubFetch([{ status: 200, body: { unexpected: true } }]);
+  const r = await makeClient().findOpenPull('feature', 'develop');
+  assert.equal(r, null);
+});
diff --git a/app/lib/inputs.js b/app/lib/inputs.js
new file mode 100644
index 0000000..a221542
--- /dev/null
+++ b/app/lib/inputs.js
@@ -0,0 +1,81 @@
+import { log } from './util.js';
+
+/**
+ * 從環境變數讀取並驗證所有輸入參數。
+ *
+ * @returns {{
+ *   serverUrl: string,
+ *   repository: string,
+ *   owner: string,
+ *   repo: string,
+ *   token: string,
+ *   sourceBranch: string,
+ *   targetBranch: string,
+ *   opencode: { baseUrl: string, model: string, provider: string },
+ *   language: string,
+ *   maxDiffChars: number,
+ *   workspace: string,
+ * }}
+ */
+export function loadInputs() {
+  const serverUrl = trimSlash(required('GITEA_SERVER_URL'));
+  const repository = required('GITEA_REPOSITORY'); // owner/repo
+  const token = required('GITEA_TOKEN');
+  const sourceBranch = required('SOURCE_BRANCH');
+  const targetBranch = required('TARGET_BRANCH');
+
+  const [owner, repo] = repository.split('/');
+  if (!owner || !repo) {
+    throw new Error(`GITEA_REPOSITORY 格式應為 owner/repo，收到: ${repository}`);
+  }
+
+  if (sourceBranch === targetBranch) {
+    throw new Error(`來源分支與目標分支不可相同: ${sourceBranch}`);
+  }
+
+  const opencode = {
+    baseUrl: trimSlash(process.env.OPENCODE_BASE_URL || ''),
+    model: process.env.OPENCODE_MODEL || '',
+    provider: process.env.OPENCODE_PROVIDER || '',
+  };
+
+  // PR 標題/描述固定使用繁體中文，diff 截斷上限固定，皆不透過參數控制
+  const language = 'Traditional Chinese (繁體中文)';
+  const maxDiffChars = 60000;
+  const workspace = process.env.GITHUB_WORKSPACE || process.cwd();
+
+  return {
+    serverUrl,
+    repository,
+    owner,
+    repo,
+    token,
+    sourceBranch,
+    targetBranch,
+    opencode,
+    language,
+    maxDiffChars,
+    workspace,
+  };
+}
+
+function required(name) {
+  const value = process.env[name];
+  if (!value || !value.trim()) {
+    throw new Error(`缺少必要的環境變數: ${name}`);
+  }
+  return value.trim();
+}
+
+function trimSlash(url) {
+  return url.replace(/\/+$/, '');
+}
+
+/** 印出輸入摘要（遮蔽敏感資訊）。 */
+export function logInputs(inputs) {
+  log.info(`Gitea Server : ${inputs.serverUrl}`);
+  log.info(`Repository   : ${inputs.repository}`);
+  log.info(`來源分支     : ${inputs.sourceBranch}`);
+  log.info(`目標分支     : ${inputs.targetBranch}`);
+  log.info(`opencode     : provider=${inputs.opencode.provider || '(未設定)'} model=${inputs.opencode.model || '(未設定)'} baseUrl=${inputs.opencode.baseUrl || '(未設定)'}`);
+}
diff --git a/app/lib/opencode.js b/app/lib/opencode.js
new file mode 100644
index 0000000..43f312e
--- /dev/null
+++ b/app/lib/opencode.js
@@ -0,0 +1,239 @@
+import { writeFileSync, mkdtempSync, rmSync } from 'node:fs';
+import { tmpdir, homedir } from 'node:os';
+import { join, dirname } from 'node:path';
+import { run, log, maskSecrets } from './util.js';
+
+/**
+ * 透過 opencode CLI 分析 git diff，產生 PR 標題與描述。
+ */
+export class OpenCode {
+  /**
+   * @param {object} opts
+   * @param {string} opts.baseUrl
+   * @param {string} opts.model
+   * @param {string} opts.provider
+   * @param {string} [opts.language]
+   */
+  constructor({ baseUrl, model, provider, language = 'Traditional Chinese (繁體中文)' }) {
+    this.baseUrl = baseUrl;
+    this.model = model;
+    this.provider = provider;
+    this.language = language;
+  }
+
+  /** 是否有足夠設定可以呼叫 opencode。 */
+  isConfigured() {
+    return Boolean(this.baseUrl && this.model && this.provider);
+  }
+
+  /**
+   * 在暫存目錄寫出 opencode.json，將自訂 provider 設為 OpenAI 相容端點。
+   *
+   * @returns {string} config 檔路徑
+   */
+  _writeConfig() {
+    const dir = mkdtempSync(join(tmpdir(), 'opencode-'));
+    const options = { baseURL: this.baseUrl };
+
+    const config = {
+      $schema: 'https://opencode.ai/config.json',
+      provider: {
+        [this.provider]: {
+          npm: '@ai-sdk/openai-compatible',
+          name: this.provider,
+          options,
+          models: {
+            [this.model]: { name: this.model },
+          },
+        },
+      },
+    };
+
+    const path = join(dir, 'opencode.json');
+    writeFileSync(path, JSON.stringify(config, null, 2));
+    return path;
+  }
+
+  /**
+   * 呼叫 opencode 產生標題與描述。
+   *
+   * @param {object} ctx
+   * @param {string} ctx.sourceBranch
+   * @param {string} ctx.targetBranch
+   * @param {string} ctx.commitMessages
+   * @param {string} ctx.diffStat
+   * @param {string} ctx.diff 已截斷的 diff
+   * @returns {Promise<{ title: string, description: string } | null>}
+   */
+  async summarize(ctx) {
+    if (!this.isConfigured()) {
+      log.warn('opencode 參數不完整（需要 base_url / model / provider），略過 AI 摘要');
+      return null;
+    }
+
+    const configPath = this._writeConfig();
+    const prompt = buildPrompt({ ...ctx, language: this.language });
+
+    try {
+      log.info(`呼叫 opencode（${this.provider}/${this.model}）分析 diff...`);
+      const result = run(
+        'opencode',
+        ['run', '--model', `${this.provider}/${this.model}`, prompt],
+        {
+          cwd: tmpdir(),
+          env: {
+            ...process.env,
+            OPENCODE_CONFIG: configPath,
+            // 確保 opencode 有可寫的 HOME / 設定目錄
+            HOME: process.env.HOME || homedir(),
+          },
+          timeout: 5 * 60 * 1000,
+        },
+      );
+
+      if (result.status !== 0) {
+        const stderr = maskSecrets(result.stderr);
+        const shown = stderr.length > 2000
+          ? `${stderr.slice(0, 2000)}\n…（錯誤訊息過長，已截斷，僅顯示前 2000 字元）`
+          : stderr;
+        log.warn(`opencode 執行失敗 (${result.status})：${shown}`);
+        return null;
+      }
+
+      const parsed = extractResult(result.stdout);
+      if (!parsed) {
+        log.warn('無法從 opencode 輸出解析出標題/描述');
+        return null;
+      }
+      return parsed;
+    } finally {
+      // 清理 _writeConfig 建立的暫存設定目錄，避免堆積
+      rmSync(dirname(configPath), { recursive: true, force: true });
+    }
+  }
+}
+
+function buildPrompt({ sourceBranch, targetBranch, commitMessages, diffStat, diff, language }) {
+  return [
+    `You are an assistant that writes high-quality Pull Request titles and descriptions.`,
+    `Analyze the following git changes for a PR merging branch "${sourceBranch}" into "${targetBranch}".`,
+    ``,
+    `Write the title and description in ${language}.`,
+    `The title should be a concise one-line summary (ideally following Conventional Commits style, e.g. "feat: ...").`,
+    `The description should be Markdown and include: a short summary, a bullet list of key changes, and any notable impact or risk.`,
+    ``,
+    `Respond with ONLY a single JSON object, no code fences, no extra text:`,
+    `{"title": "...", "description": "..."}`,
+    ``,
+    `=== Commits ===`,
+    commitMessages || '(no commit messages)',
+    ``,
+    `=== Changed files (stat) ===`,
+    diffStat || '(no stat)',
+    ``,
+    `=== Diff ===`,
+    diff || '(no diff)',
+  ].join('\n');
+}
+
+/** 去除 ANSI 控制碼。 */
+function stripAnsi(text) {
+  // eslint-disable-next-line no-control-regex
+  return text.replace(/\x1b\[[0-9;]*[a-zA-Z]/g, '');
+}
+
+/**
+ * 從 opencode 輸出中擷取含 title 的 JSON 物件並解析。
+ *
+ * @param {string} stdout
+ * @returns {{ title: string, description: string } | null}
+ */
+export function extractResult(stdout) {
+  const text = stripAnsi(stdout || '');
+
+  // 掃描所有平衡的 {...} 區塊，挑出第一個能成功解析且含 title 的物件
+  for (const candidate of findJsonObjects(text)) {
+    // LLM 常在字串值內輸出未跳脫的換行，先嘗試原始解析，失敗再嘗試修正
+    for (const variant of [candidate, escapeControlCharsInStrings(candidate)]) {
+      try {
+        const obj = JSON.parse(variant);
+        if (obj && typeof obj === 'object' && obj.title) {
+          return {
+            title: String(obj.title).trim(),
+            description: String(obj.description || '').trim(),
+          };
+        }
+      } catch {
+        // 試下一個變體 / 候選
+      }
+    }
+  }
+  return null;
+}
+
+/** 將字串值內未跳脫的控制字元（換行、tab 等）跳脫，修正 LLM 常見的無效 JSON。 */
+function escapeControlCharsInStrings(text) {
+  let out = '';
+  let inString = false;
+  let escape = false;
+  for (let i = 0; i < text.length; i++) {
+    const ch = text[i];
+    if (inString) {
+      if (escape) {
+        out += ch;
+        escape = false;
+        continue;
+      }
+      if (ch === '\\') {
+        out += ch;
+        escape = true;
+        continue;
+      }
+      if (ch === '"') {
+        out += ch;
+        inString = false;
+        continue;
+      }
+      if (ch === '\n') { out += '\\n'; continue; }
+      if (ch === '\r') { out += '\\r'; continue; }
+      if (ch === '\t') { out += '\\t'; continue; }
+      out += ch;
+    } else {
+      out += ch;
+      if (ch === '"') inString = true;
+    }
+  }
+  return out;
+}
+
+/** 以括號平衡方式找出文字中所有最外層的 {...} 區塊。 */
+function findJsonObjects(text) {
+  const objects = [];
+  let depth = 0;
+  let start = -1;
+  let inString = false;
+  let escape = false;
+
+  for (let i = 0; i < text.length; i++) {
+    const ch = text[i];
+    if (inString) {
+      if (escape) escape = false;
+      else if (ch === '\\') escape = true;
+      else if (ch === '"') inString = false;
+      continue;
+    }
+    if (ch === '"') {
+      inString = true;
+    } else if (ch === '{') {
+      if (depth === 0) start = i;
+      depth++;
+    } else if (ch === '}') {
+      depth--;
+      if (depth === 0 && start !== -1) {
+        objects.push(text.slice(start, i + 1));
+        start = -1;
+      }
+    }
+  }
+  return objects;
+}
diff --git a/app/lib/opencode.test.js b/app/lib/opencode.test.js
new file mode 100644
index 0000000..7ead244
--- /dev/null
+++ b/app/lib/opencode.test.js
@@ -0,0 +1,41 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { extractResult } from './opencode.js';
+
+test('extractResult: 解析乾淨的 JSON', () => {
+  const r = extractResult('{"title":"標題","description":"描述"}');
+  assert.deepEqual(r, { title: '標題', description: '描述' });
+});
+
+test('extractResult: 忽略 JSON 前後的雜訊文字', () => {
+  const r = extractResult('以下是結果：\n{"title":"T","description":"D"}\n完成');
+  assert.deepEqual(r, { title: 'T', description: 'D' });
+});
+
+test('extractResult: 修正字串值內未跳脫的換行', () => {
+  // LLM 常輸出字串內含真實換行的無效 JSON
+  const r = extractResult('{"title":"T","description":"第一行\n第二行"}');
+  assert.equal(r.title, 'T');
+  assert.equal(r.description, '第一行\n第二行');
+});
+
+test('extractResult: 去除 ANSI 控制碼後解析', () => {
+  const r = extractResult('\x1b[32m{"title":"T","description":"D"}\x1b[0m');
+  assert.deepEqual(r, { title: 'T', description: 'D' });
+});
+
+test('extractResult: 挑出第一個含 title 的物件', () => {
+  const r = extractResult('{"foo":1}\n{"title":"對的","description":"D"}');
+  assert.equal(r.title, '對的');
+});
+
+test('extractResult: 無有效物件回傳 null', () => {
+  assert.equal(extractResult('沒有任何 JSON'), null);
+  assert.equal(extractResult(''), null);
+  assert.equal(extractResult('{"description":"缺少 title"}'), null);
+});
+
+test('extractResult: description 缺漏時以空字串補上', () => {
+  const r = extractResult('{"title":"只有標題"}');
+  assert.deepEqual(r, { title: '只有標題', description: '' });
+});
diff --git a/app/lib/util.js b/app/lib/util.js
new file mode 100644
index 0000000..d0463d7
--- /dev/null
+++ b/app/lib/util.js
@@ -0,0 +1,72 @@
+import { spawnSync } from 'node:child_process';
+
+/**
+ * 執行外部指令並回傳結果（不會因為非零結束碼而 throw）。
+ *
+ * @param {string} command 要執行的指令
+ * @param {string[]} args 指令參數
+ * @param {object} [options] spawnSync 額外設定（cwd、env、input、maxBuffer...）
+ * @returns {{ status: number, stdout: string, stderr: string }}
+ */
+export function run(command, args = [], options = {}) {
+  const result = spawnSync(command, args, {
+    encoding: 'utf8',
+    maxBuffer: 64 * 1024 * 1024, // 64MB，避免大型 diff 被截斷
+    ...options,
+  });
+
+  if (result.error) {
+    return { status: 1, stdout: '', stderr: String(result.error.message || result.error) };
+  }
+
+  return {
+    status: typeof result.status === 'number' ? result.status : 1,
+    stdout: result.stdout || '',
+    stderr: result.stderr || '',
+  };
+}
+
+/**
+ * 執行外部指令，若結束碼非零則 throw。
+ *
+ * @param {string} command
+ * @param {string[]} args
+ * @param {object} [options]
+ * @returns {string} stdout（已 trim）
+ */
+export function runOrThrow(command, args = [], options = {}) {
+  const result = run(command, args, options);
+  if (result.status !== 0) {
+    const detail = (result.stderr || result.stdout || '').trim();
+    throw new Error(`指令失敗 (${result.status}): ${command} ${args.join(' ')}\n${detail}`);
+  }
+  return result.stdout.trim();
+}
+
+const ICONS = { info: 'ℹ️', warn: '⚠️', error: '❌', success: '✅', step: '▶️' };
+
+/** 簡單的分級日誌輸出。 */
+export const log = {
+  info: (msg) => console.log(`${ICONS.info}  ${msg}`),
+  warn: (msg) => console.log(`${ICONS.warn}  ${msg}`),
+  error: (msg) => console.error(`${ICONS.error}  ${msg}`),
+  success: (msg) => console.log(`${ICONS.success}  ${msg}`),
+  step: (msg) => console.log(`\n${ICONS.step}  ${msg}`),
+};
+
+/**
+ * 將敏感字串（如 token）從文字中遮蔽，避免寫入日誌。
+ *
+ * @param {string} text
+ * @param {string[]} secrets
+ * @returns {string}
+ */
+export function maskSecrets(text, secrets = []) {
+  let masked = String(text ?? '');
+  for (const secret of secrets) {
+    if (secret && secret.length >= 4) {
+      masked = masked.split(secret).join('***');
+    }
+  }
+  return masked;
+}
diff --git a/app/lib/util.test.js b/app/lib/util.test.js
new file mode 100644
index 0000000..13d2bc2
--- /dev/null
+++ b/app/lib/util.test.js
@@ -0,0 +1,37 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { maskSecrets, run } from './util.js';
+
+test('maskSecrets: 遮蔽出現的祕密字串', () => {
+  const out = maskSecrets('token is abcd1234 here', ['abcd1234']);
+  assert.equal(out, 'token is *** here');
+});
+
+test('maskSecrets: 遮蔽 URL 內嵌的 token', () => {
+  const out = maskSecrets('https://oauth2:abcd1234@host/repo.git', ['abcd1234']);
+  assert.ok(!out.includes('abcd1234'));
+});
+
+test('maskSecrets: 太短(<4)的祕密不遮蔽以免誤傷', () => {
+  assert.equal(maskSecrets('abc here', ['abc']), 'abc here');
+});
+
+test('maskSecrets: 多個祕密與空值都安全處理', () => {
+  const out = maskSecrets('aaaa bbbb', ['aaaa', '', undefined, 'bbbb']);
+  assert.equal(out, '*** ***');
+});
+
+test('maskSecrets: 非字串輸入回傳空字串', () => {
+  assert.equal(maskSecrets(null), '');
+});
+
+test('run: 非零結束碼不丟例外並回傳 status', () => {
+  const r = run('node', ['-e', 'process.exit(3)']);
+  assert.equal(r.status, 3);
+});
+
+test('run: 指令不存在時回傳 status=1 與錯誤訊息', () => {
+  const r = run('a-command-that-does-not-exist-xyz', []);
+  assert.equal(r.status, 1);
+  assert.ok(r.stderr.length > 0);
+});
diff --git a/app/package.json b/app/package.json
new file mode 100644
index 0000000..48c5e84
--- /dev/null
+++ b/app/package.json
@@ -0,0 +1,15 @@
+{
+  "name": "ai-pull-request",
+  "version": "1.0.0",
+  "description": "使用 opencode 分析 git diff 自動產生 PR 標題與描述，並透過 Gitea API 建立 Pull Request",
+  "type": "module",
+  "main": "index.js",
+  "scripts": {
+    "start": "node index.js",
+    "test": "node --test"
+  },
+  "engines": {
+    "node": ">=18"
+  },
+  "license": "MIT"
+}
diff --git a/entrypoint.sh b/entrypoint.sh
index c8c429c..9a8fb15 100644
--- a/entrypoint.sh
+++ b/entrypoint.sh
@@ -1,11 +1,9 @@
 #!/bin/bash
+set -euo pipefail
 
-echo "Gitea Server Url: $GITEA_SERVER_URL"
+echo "🚀 ai-pull-request action 啟動"
+echo "   Repository: ${GITEA_REPOSITORY:-?}"
+echo "   ${SOURCE_BRANCH:-?} → ${TARGET_BRANCH:-?}"
 
-echo "Gitea Repository: $GITEA_REPOSITORY"
-
-echo "Gitea Token: $GITEA_TOKEN"
-
-echo "Text: $TEXT"
-
-echo "text=$TEXT" >> "$GITHUB_OUTPUT"
\ No newline at end of file
+# Node.js 應用程式進入點
+exec node /app/index.js