[Cherry-Pick][CI]Fix multistep MTP in splitewise-prefill mode (#5723)

[freeliuzc]

Motivation

💡 If this PR is a Cherry Pick, the PR title needs to follow the format by adding the [Cherry-Pick] label at the very beginning and appending the original PR ID at the end. For example, [Cherry-Pick][CI] Add check trigger and logic(#5191)

💡 如若此PR是Cherry Pick，PR标题需遵循格式，在最开始加上[Cherry-Pick]标签，以及最后面加上原PR ID，例如[Cherry-Pick][CI] Add check trigger and logic(#5191)

Modifications

Usage or Command

Accuracy Tests

Checklist

• Add at least a tag in the PR title.
  • Tag list: [[FDConfig],[APIServer],[Engine], [Scheduler], [PD Disaggregation], [Executor], [Graph Optimization], [Speculative Decoding], [RL], [Models], [Quantization], [Loader], [OP], [KVCache], [DataProcessor], [BugFix], [Docs], [CI], [Optimization], [Feature], [Benchmark], [Others], [XPU], [HPU], [GCU], [DCU], [Iluvatar], [Metax]]
  • You can add new tags based on the PR content, but the semantics must be clear.
• Format your code, run pre-commit before commit.
• Add unit tests. Please write the reason in this PR if no unit tests.
• Provide accuracy results.
• If the current PR is submitting to the release branch, make sure the PR has been submitted to the develop branch, then cherry-pick it to the release branch with the [Cherry-Pick] PR tag.

[paddle-bot]

Thanks for your contribution!

[Copilot]

Pull request overview

这是一个Cherry-Pick PR，旨在修复MTP（多步投机解码）在splitwise-prefill模式下的问题。该修复在配置后处理阶段添加了逻辑，当使用MTP方法且处于prefill角色时，将投机解码的token数量和模型步数限制为1。

主要变更：

• 在配置后处理方法中添加了MTP在prefill模式下的特殊处理逻辑
• 当检测到speculative_config使用"mtp"方法且splitwise_role为"prefill"时，自动调整配置参数

[Copilot]

缺少闭合引号。字符串 "prefill 后面应该有一个双引号来闭合字符串。这会导致语法错误。应该改为 "prefill"。

Suggested change

	# adjust speculative config
	if self.speculative_config is not None and self.speculative_config.method == "mtp":
	if self.scheduler_config.splitwise_role == "prefill:
	# adjust speculative config
	if self.speculative_config is not None and self.speculative_config.method == "mtp":
	if self.scheduler_config.splitwise_role == "prefill":

[Copilot]

此处有两个连续的空行（1707和1708），而代码库的其他部分通常只使用一个空行来分隔代码块。为保持一致性，建议只保留一个空行。

Suggested change

[Copilot]

新增的MTP在splitwise prefill模式下的配置调整逻辑缺少相应的单元测试。建议在tests/utils/test_config.py中添加测试用例，验证当speculative_config.method为"mtp"且scheduler_config.splitwise_role为"prefill"时，num_speculative_tokens和num_model_steps是否正确设置为1。

[Copilot]

PR描述中缺少关键信息。根据要求，PR描述至少应说明为什么进行这些修改以及正在解决什么问题。当前PR描述只有模板内容，没有填写Motivation（动机）、Modifications（修改内容）等必要信息。建议补充：1) 此修复解决的具体问题是什么；2) 为什么在splitwise prefill模式下需要将num_speculative_tokens和num_model_steps设置为1；3) 此修复如何解决问题。

[codecov-commenter]

Codecov Report

❌ Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release/online/20251131@1b74540). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/config.py	25.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@                    Coverage Diff                     @@
##             release/online/20251131    #5724   +/-   ##
==========================================================
  Coverage                           ?   59.08%           
==========================================================
  Files                              ?      319           
  Lines                              ?    39106           
  Branches                           ?     5893           
==========================================================
  Hits                               ?    23105           
  Misses                             ?    14148           
  Partials                           ?     1853           

Flag	Coverage Δ
GPU	59.08% <25.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.