feat: 前置驗證納入 git push 認證檢查

git push 走 askpass + HTTP 認證，與 Gitea REST API 是兩套機制，API token
有效不代表 push 能用（曾出現 askpass 無法執行、could not read Username 而
push 失敗）。新增 git.js verifyRemoteAccess() 以相同 askpass + remote URL
跑唯讀 git ls-remote，preflight 呼叫並在失敗時 exit 1，提前攔下設定問題。

新增 git.test.js 對 verifyRemoteAccess 的測試（成功、失敗不丟例外、token
不外洩、askpass 清理）。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/git.js

@@ -258,6 +258,24 @@ export function isBotAutoCommit(repoDir, _spawnSync = spawnSync) {
   return getHeadCommitMessage(repoDir, _spawnSync).includes(BOT_COMMIT_MARKER);
 }
 
+/**
+ * 用與 push 相同的 askpass + remote URL 機制跑一次唯讀的 `git ls-remote`，
+ * 驗證 git 對 remote 的認證與連線是否可用（不會寫入任何東西）。
+ * 這條路徑與 Gitea REST API 不同，API token 有效不代表 git push 認證一定可用，
+ * 所以放在前置驗證可以提前抓出 askpass 無法執行或 HTTP 認證失敗的問題。
+ */
+export function verifyRemoteAccess(workspace, _spawnSync = spawnSync) {
+  const run = makeRunner(_spawnSync);
+  try {
+    return withAskpass(workspace, credEnv => {
+      run(['ls-remote', remoteUrl, PR_HEAD_BRANCH || 'HEAD'], workspace, credEnv);
+      return { ok: true };
+    });
+  } catch (e) {
+    return { ok: false, error: e.message };
+  }
+}
+
 /**
  * Clone PR head branch to workspace/repo (idempotent)
  */

app/git.test.js

@@ -3,7 +3,7 @@ import assert from 'node:assert/strict';
 import fs from 'fs';
 import os from 'os';
 import path from 'path';
-import { commitAndPush, cloneRepo, SYNC_PATHS, BOT_COMMIT_MARKER, getHeadCommitMessage, isBotAutoCommit, mergeInstructionText } from './git.js';
+import { commitAndPush, cloneRepo, verifyRemoteAccess, SYNC_PATHS, BOT_COMMIT_MARKER, getHeadCommitMessage, isBotAutoCommit, mergeInstructionText } from './git.js';
 
 // --- helpers ---
 function makeTmpWorkspace() {
@@ -334,3 +334,47 @@ describe('cloneRepo', () => {
     assert.equal(isBotAutoCommit(workspace, spawn), true);
   });
 });
+
+describe('verifyRemoteAccess', () => {
+  let workspace;
+  before(() => { workspace = fs.mkdtempSync(path.join(os.tmpdir(), 'git-lsremote-')); });
+  after(() => { fs.rmSync(workspace, { recursive: true, force: true }); });
+
+  it('runs git ls-remote with the askpass credential env and reports ok on success', () => {
+    const calls = [];
+    const spawn = (cmd, args, opts) => {
+      calls.push({ cmd, args, opts });
+      return { status: 0, stdout: 'abc123\tHEAD', stderr: '', error: null };
+    };
+    const result = verifyRemoteAccess(workspace, spawn);
+    assert.deepEqual(result, { ok: true });
+    const lsRemote = calls.find(c => c.args[0] === 'ls-remote');
+    assert.ok(lsRemote, 'expected git ls-remote to run');
+    assert.ok(lsRemote.opts?.env?.GIT_ASKPASS, 'expected GIT_ASKPASS env for ls-remote');
+  });
+
+  it('does not leak the token in ls-remote args', () => {
+    const calls = [];
+    const spawn = (cmd, args, opts) => {
+      calls.push({ args });
+      return { status: 0, stdout: '', stderr: '', error: null };
+    };
+    verifyRemoteAccess(workspace, spawn);
+    for (const { args } of calls) {
+      assert.ok(!args.join(' ').includes('test-token'), `Token leaked in git args: ${args.join(' ')}`);
+    }
+  });
+
+  it('reports failure (not throw) when git ls-remote fails', () => {
+    const spawn = () => ({ status: 128, stdout: '', stderr: 'fatal: could not read Username', error: null });
+    const result = verifyRemoteAccess(workspace, spawn);
+    assert.equal(result.ok, false);
+    assert.match(result.error, /could not read Username/);
+  });
+
+  it('cleans up the askpass script after running', () => {
+    verifyRemoteAccess(workspace, () => ({ status: 0, stdout: '', stderr: '', error: null }));
+    const leftover = fs.readdirSync(workspace).filter(f => f.endsWith('.git-askpass.sh'));
+    assert.equal(leftover.length, 0, 'askpass script was not cleaned up');
+  });
+});

app/main.js

@@ -17,7 +17,7 @@ async function main() {
   line(`repo=${GITEA_REPOSITORY}  PR=#${PR_NUMBER}`);
   line(`${PR_HEAD_BRANCH} -> ${PR_BASE_BRANCH}`);
 
-  if (!(await runPreflight())) {
+  if (!(await runPreflight(WORKSPACE))) {
     error('前置驗證未通過，終止流程');
     section('Pipeline 結束');
     process.exit(1);

app/preflight.js

@@ -9,6 +9,7 @@ import {
   PR_NUMBER,
   getLLMConfig,
 } from './config.js';
+import { verifyRemoteAccess } from './git.js';
 import { step, line, ok, error } from './log.js';
 
 const httpsAgent = GITEA_SKIP_TLS_VERIFY ? new https.Agent({ rejectUnauthorized: false }) : undefined;
@@ -92,7 +93,7 @@ export async function verifyLLM() {
  * 集中執行所有驗證相關設定的前置檢查；全部通過回傳 true，任一失敗回傳 false。
  * 僅做唯讀的認證/連線確認，不發布任何 comment。
  */
-export async function runPreflight() {
+export async function runPreflight(workspace = process.env.GITHUB_WORKSPACE || '/workspace') {
   step('Step1.5', '前置驗證（驗證相關設定）');
 
   const env = checkRequiredEnv();
@@ -117,6 +118,13 @@ export async function runPreflight() {
   if (comment.skipped) line('未提供 GITEA_COMMENT_TOKEN，comment 將沿用 GITEA_TOKEN');
   else ok('GITEA_COMMENT_TOKEN 可用');
 
+  const remote = verifyRemoteAccess(workspace);
+  if (!remote.ok) {
+    error(`git push 認證/連線驗證失敗（ls-remote）: ${remote.error}`);
+    return false;
+  }
+  ok('git remote 認證可用（ls-remote 成功）');
+
   const llm = await verifyLLM();
   if (!llm.ok) {
     error(`LLM 驗證失敗: ${llm.error}`);