[fix][prompt] fix ut map -> list problem

[caijialin0626]

What type of PR is this?
fix

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• [x] The description of this PR title is user-oriented and clear enough for others to understand.
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PR Title: [fix][prompt] fix unit test flakiness in SaveDraft with snippets

(Optional) Translate the PR title into Chinese
修复 SaveDraft 中 snippets 相关单元测试的不稳定问题

(Optional) More detailed description for this PR
en:
Fixed flaky unit test in TestManageRepoImpl_SaveDraft/create_draft_with_snippets that was failing intermittently due to order dependency when converting map to slice. The test was asserting specific array indices for relations, but Go map iteration order is undefined, causing non-deterministic test results.

Solution:
• Replaced index-based assertions with content-based verification using a map lookup
• Maintained all existing validation logic while eliminating order dependency
• Added descriptive error messages for better debugging

zh:
修复了 TestManageRepoImpl_SaveDraft/create_draft_with_snippets 中的不稳定测试问题，该测试因为 map 转 slice 时的顺序依赖而间歇性失败。测试代码断言特定的数组索引对应关系，但 Go 的 map 迭代顺序是未定义的，导致测试结果不确定。

解决方案：
• 将基于索引的断言替换为基于内容的验证，使用 map 查找
• 保持所有现有验证逻辑的同时消除了顺序依赖
• 添加了描述性错误信息以便更好地调试

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@           Coverage Diff           @@
##             main     #363   +/-   ##
=======================================
  Coverage   69.41%   69.41%           
=======================================
  Files         616      616           
  Lines       57881    57881           
=======================================
  Hits        40179    40179           
  Misses      14765    14765           
  Partials     2937     2937           

Flag	Coverage Δ
unittests	69.41% <ø> (ø)

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