Fix review comments: Use job outputs instead of shared filesystem

- Replace /tmp/old_value.txt with job outputs for passing data between jobs
- Use vars.REPO instead of github.repository for API calls
- This fixes the issue where jobs cannot share filesystem

Co-Authored-By: Claude (mimo-v2-flash) <noreply@anthropic.com>

Author: WhiteElephantIsNotARobot

.github/workflows/update-system-prompt.yml

@@ -35,19 +35,21 @@ jobs:
           SYSTEM_PROMPT_CONTENT=$(cat system_prompt.md)
 
           # 获取旧变量值
-          OLD_VALUE=$(gh api /repos/${{ github.repository }}/actions/variables/SYSTEM_PROMPT --jq '.value' 2>/dev/null || echo "")
+          OLD_VALUE=$(gh api /repos/${{ vars.REPO }}/actions/variables/SYSTEM_PROMPT --jq '.value' 2>/dev/null || echo "")
 
           # 更新 GitHub Actions 变量
           gh api --method PATCH \
-            /repos/${{ github.repository }}/actions/variables/SYSTEM_PROMPT \
+            /repos/${{ vars.REPO }}/actions/variables/SYSTEM_PROMPT \
             -f name=SYSTEM_PROMPT \
             -f value="$SYSTEM_PROMPT_CONTENT"
 
           echo "✓ SYSTEM_PROMPT 变量已更新"
           echo "文件大小: $(wc -c < system_prompt.md) 字符"
 
-          # 保存旧值到文件供下一步使用
-          echo "$OLD_VALUE" > /tmp/old_value.txt
+          # 将旧值输出到下一步
+          echo "old_value<<EOF" >> $GITHUB_OUTPUT
+          echo "$OLD_VALUE" >> $GITHUB_OUTPUT
+          echo "EOF" >> $GITHUB_OUTPUT
 
   create-diff-issue:
     needs: update
@@ -65,8 +67,8 @@ jobs:
 
       - name: Create diff issue
         run: |
-          # 读取旧值
-          OLD_VALUE=$(cat /tmp/old_value.txt)
+          # 读取旧值（来自 update job 的输出）
+          OLD_VALUE="${{ needs.update.outputs.old_value }}"
           # 读取新值
           NEW_VALUE=$(cat system_prompt.md)