Fix vllm_api_general_chat endpoint join for base URLs without trailing slash

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PR Type / PR类型

• Feature（功能新增）
• Bugfix（Bug 修复）
• Docs（文档更新）
• CI/CD（持续集成/持续部署）
• Refactor（代码重构）
• Perf（性能优化）
• Dependency（依赖项更新）
• Test-Cases（测试用例更新）
• Other（其他）

Related Issue | 关联 Issue

🔍 Motivation / 变更动机

vllm_api_general_chat incorrectly builds request URLs when url contains a path but has no trailing /, causing requests to drop the last path segment (e.g., .../deepseek_v4 -> .../member1/v1/chat/completions).
This leads to empty predictions and abnormal token/time metrics because the intended endpoint is not reached.

📝 Modification / 修改内容

• URL normalization before endpoint join

  • In VLLMCustomAPIChat._get_url, normalize base_url to .../ before urllib.parse.urljoin.
  • Ensures both http://host/path and http://host/path/ resolve to http://host/path/v1/chat/completions.

• Focused unit coverage for regression

  • Added a case in tests/UT/models/api_models/test_vllm_custom_api_chat.py::test_get_url for a custom path URL without trailing slash.

normalized_base_url = f"{self.base_url.rstrip('/')}/"
url = urllib.parse.urljoin(normalized_base_url, "v1/chat/completions")

📐 Associated Test Results / 关联测试结果

N/A

⚠️ BC-breaking (Optional) / 向后不兼容变更（可选）

No backward-incompatible interface changes. This is a URL construction correctness fix.

⚠️ Performance degradation (Optional) / 性能下降（可选）

None expected.

🌟 Use cases (Optional) / 使用案例（可选）

N/A

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• Pre-commit or other linting tools are used to fix the potential lint issues. / 使用预提交或其他 linting 工具来修复潜在的 lint 问题。
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests. / 修复的 Bug 已完全由单元测试覆盖，导致 Bug 的情况应在单元测试中添加。
• The modification is covered by complete unit tests. If not, please add more unit tests to ensure the correctness. / 此拉取请求中的修改已完全由单元测试覆盖。如果不是，请添加更多单元测试以确保正确性。
• All relevant documentation (API docs, docstrings, example tutorials) has been updated to reflect these changes. / 所有相关文档（API 文档、文档字符串、示例教程）已更新以反映这些更改。

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects. / 如果此拉取请求对下游或其他相关项目有潜在影响，应在那些项目中测试此 PR。
• CLA has been signed and all committers have signed the CLA in this PR. / CLA 已签署，且本 PR 中的所有提交者均已签署 CLA。

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[Copilot]

Pull request overview

Fixes incorrect URL construction in VLLMCustomAPIChat when a custom base URL contains a subpath but lacks a trailing slash, ensuring requests hit the intended /v1/chat/completions endpoint and preventing empty predictions/incorrect metrics.

Changes:

• Normalize base_url to always end with / before urllib.parse.urljoin in VLLMCustomAPIChat._get_url.
• Add a unit test case covering a custom subpath URL without a trailing slash.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
ais_bench/benchmark/models/api_models/vllm_custom_api_chat.py	Normalizes base_url prior to joining the chat-completions endpoint to avoid dropping the last path segment.
tests/UT/models/api_models/test_vllm_custom_api_chat.py	Adds a regression assertion for subpath base URLs without a trailing slash.

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