diff --git a/app/lib/git.js b/app/lib/git.js
index 28b9bfd..eb6c880 100644
--- a/app/lib/git.js
+++ b/app/lib/git.js
@@ -97,25 +97,28 @@ export class Git {
    * @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
-    const tmp = `__conflict_check_${target}`;
+    // 建立暫時的本地 target 分支，嘗試以 --no-commit 合併 source。
+    // 名稱帶 PID，避免並行或前次殘留造成命名衝突。
+    const tmp = `__conflict_check_${target}_${process.pid}`;
     this._git(['checkout', '-B', tmp, `refs/remotes/pr/${target}`]);
 
-    const merge = this._git(['merge', '--no-commit', '--no-ff', `refs/remotes/pr/${source}`]);
-    let hasConflict = merge.status !== 0;
-    let files = [];
+    try {
+      const merge = this._git(['merge', '--no-commit', '--no-ff', `refs/remotes/pr/${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);
+      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]);
     }
-
-    // 還原工作區
-    this._git(['merge', '--abort']);
-    this._git(['checkout', '--detach']);
-    this._git(['branch', '-D', tmp]);
-
-    return { hasConflict, files };
   }
 
   /**