diff --git a/Dockerfile b/Dockerfile
index 484bf92..c55c659 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,5 +1,6 @@
 FROM node:20-slim
 
+# force rebuild to ensure git is installed
 RUN apt-get update && apt-get install -y --no-install-recommends \
     git \
     && rm -rf /var/lib/apt/lists/*
diff --git a/app/git.js b/app/git.js
index 1b89d22..36b01a9 100644
--- a/app/git.js
+++ b/app/git.js
@@ -1,25 +1,36 @@
-import fs from 'fs';
+import { spawnSync } from 'child_process';
 import path from 'path';
-import { commitFile } from './gitea.js';
-import { FINDINGS_PATH } from './config.js';
+import { GITEA_SERVER_URL, GITEA_REPOSITORY, GITEA_TOKEN, PR_HEAD_BRANCH, FINDINGS_PATH } from './config.js';
+
+function git(args, cwd) {
+  const result = spawnSync('git', args, { cwd, encoding: 'utf8' });
+  if (result.error) throw result.error;
+  if (result.status !== 0) throw new Error((result.stderr || result.stdout || '').trim());
+  return (result.stdout || '').trim();
+}
 
-/**
- * 透過 Gitea API 將 findings.json push 到來源分支（不需要 git binary）
- */
 export async function commitAndPush(workspace) {
+  const repoDir = path.join(workspace, GITEA_REPOSITORY);
+  const remoteUrl = GITEA_SERVER_URL.replace(/\/$/, '').replace('https://', `https://${GITEA_TOKEN}@`).replace('http://', `http://${GITEA_TOKEN}@`) + `/${GITEA_REPOSITORY}.git`;
+
   try {
-    const fullPath = path.join(workspace, FINDINGS_PATH);
-    const content = fs.readFileSync(fullPath, 'utf8');
-    console.log(`  [debug] FINDINGS_PATH=${FINDINGS_PATH} branch=${process.env.PR_HEAD_BRANCH} token=${process.env.GITEA_TOKEN ? '***' : 'EMPTY'}`);
-    const result = await commitFile(
-      FINDINGS_PATH,
-      content,
-      'chore: update ai-review findings [skip ci]'
-    );
-    const commitHash = result.commit?.sha?.slice(0, 7) || 'unknown';
-    console.log(`  ✅ persisted findings  commit=${commitHash}  push=${process.env.PR_HEAD_BRANCH}`);
+    git(['config', 'user.email', 'ai-review[bot]@gitea'], repoDir);
+    git(['config', 'user.name', 'AI Review Bot'], repoDir);
+    git(['fetch', 'origin', PR_HEAD_BRANCH], repoDir);
+    git(['checkout', PR_HEAD_BRANCH], repoDir);
+    git(['add', FINDINGS_PATH], repoDir);
+
+    const status = git(['status', '--porcelain'], repoDir);
+    if (!status) {
+      console.log('  findings.json 無變更，跳過 commit');
+      return;
+    }
+
+    const out = git(['commit', '-m', 'chore: update ai-review findings [skip ci]'], repoDir);
+    const commitHash = out.match(/\[.+ ([a-f0-9]+)\]/)?.[1] || 'unknown';
+    git(['push', remoteUrl, PR_HEAD_BRANCH], repoDir);
+    console.log(`  ✅ persisted findings  commit=${commitHash}  push=${PR_HEAD_BRANCH}`);
   } catch (e) {
-    const detail = e.response?.data ? JSON.stringify(e.response.data) : e.message;
-    console.log(`  ⚠️  Runner failed: commit/push 失敗: ${e.response?.status || ''} ${detail}`);
+    console.log(`  ⚠️  Runner failed: commit/push 失敗: ${e.message}`);
   }
 }
diff --git a/app/gitea.js b/app/gitea.js
index 6219f5a..f8b4216 100644
--- a/app/gitea.js
+++ b/app/gitea.js
@@ -1,6 +1,6 @@
 import axios from 'axios';
 import https from 'https';
-import { GITEA_TOKEN, GITEA_SERVER_URL, GITEA_REPOSITORY, PR_NUMBER, PR_HEAD_BRANCH } from './config.js';
+import { GITEA_TOKEN, GITEA_SERVER_URL, GITEA_REPOSITORY, PR_NUMBER } from './config.js';
 
 const httpsAgent = new https.Agent({ rejectUnauthorized: false });
 const headers = () => ({ Authorization: `token ${GITEA_TOKEN}`, 'Content-Type': 'application/json' });
@@ -15,41 +15,3 @@ export async function postComment(body) {
   const resp = await axios.post(api(`/repos/${GITEA_REPOSITORY}/issues/${PR_NUMBER}/comments`), { body }, { headers: headers(), timeout: 30000, httpsAgent });
   return resp.data;
 }
-
-/**
- * 透過 Gitea API 建立或更新檔案（不需要 git binary）
- */
-export async function commitFile(filePath, content, message) {
-  const encoded = Buffer.from(content).toString('base64');
-  const url = api(`/repos/${GITEA_REPOSITORY}/contents/${filePath}`);
-
-  // 先嘗試取得現有檔案的 SHA
-  let sha;
-  try {
-    const existing = await axios.get(`${url}?ref=${PR_HEAD_BRANCH}`, { headers: headers(), httpsAgent, timeout: 15000 });
-    sha = existing.data.sha;
-    console.log(`  [debug] 取得現有檔案 SHA=${sha}`);
-  } catch (e) {
-    console.log(`  [debug] 檔案不存在，將建立新檔案: ${e.response?.status || e.message}`);
-    sha = undefined;
-  }
-
-  const payload = {
-    message,
-    content: encoded,
-    branch: PR_HEAD_BRANCH,
-    ...(sha ? { sha } : {}),
-  };
-
-  console.log(`  [debug] ${sha ? 'PUT' : 'POST'} ${url} branch=${PR_HEAD_BRANCH} content_len=${encoded.length}`);
-  const resp = await axios.request({
-    method: sha ? 'put' : 'post',
-    url,
-    headers: { ...headers(), 'Content-Type': 'application/json' },
-    httpsAgent,
-    timeout: 30000,
-    data: JSON.stringify(payload),
-  });
-  console.log(`  [debug] response status=${resp.status}`);
-  return resp.data;
-}