feat: Add 'extra_body' parameter support for provider and model options

[yuguorui]

In the OpenAI Python SDK, the Completions.create method includes an extra_body parameter that lets users add custom JSON properties to the request payload. This feature is particularly useful in various scenarios—such as enabling capabilities like thinking [1][2], search, topP, temperature, and more, across different LLM providers.

Here[3] is the implementation in the Python SDK for reference.

[1] https://bailian.console.alibabacloud.com/?tab=api#/api/?type=model&url=2712576
[2] https://docs.z.ai/api-reference/llm/chat-completion
[3] https://github.com/openai/openai-python/blob/af8f606b3eef1af99f98929847f1b5baf19171ae/src/openai/resources/chat/completions.py#L76

[Copilot]

Pull request overview

This pull request adds support for an extraBody parameter to both provider-level and model-level options, allowing users to add custom JSON properties to request payloads. This feature mirrors the OpenAI Python SDK's extra_body parameter and enables capabilities like thinking, search, topP, and temperature across different LLM providers.

Key changes:

• Adds extraBody configuration option to provider and model options
• Implements logic to merge provider-level and model-level extraBody properties into the request
• Updates documentation with examples showing how to configure extraBody

Reviewed changes

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

File	Description
packages/web/src/content/docs/providers.mdx	Adds documentation and examples for the new extraBody configuration option at both provider and model levels
packages/opencode/src/provider/transform.ts	Implements the merging logic for extraBody properties from provider and model options into the request parameters

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[yuguorui]

Some typical LLM service providers (such as Alibaba BaiLian, one of Asia's largest cloud service providers) enable the thinking feature through non-standard OpenAI-compatible request body parameters. By adding support for extra_body, users can manually turn thinking on or off.

[Copilot]

Pull request overview

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

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