feat(client): allow passing async httpx client

[hassiebp]

Disclaimer: Experimental PR review

Greptile Summary

This PR adds support for passing a custom async_httpx_client (httpx.AsyncClient) to the Langfuse constructor, mirroring the existing httpx_client (sync) parameter. The async client is stored on LangfuseResourceManager, passed to AsyncLangfuseAPI, and preserved through get_client() — enabling users who need custom transport settings (e.g. proxies, SSL, connection limits) on client.async_api to supply their own client.

Key changes:

• langfuse/_client/client.py: New async_httpx_client parameter added to __init__ with docstring update.
• langfuse/_client/resource_manager.py: Parameter threaded into _initialize_instance; internally creates httpx.AsyncClient if not provided; passes it to AsyncLangfuseAPI (previously AsyncLangfuseAPI created its own internal client).
• langfuse/_client/get_client.py: async_httpx_client=instance.async_httpx_client added to _create_client_from_instance so get_client() preserves the client across singleton lookups.
• Tests cover custom client propagation through both direct construction and get_client().

The implementation is clean, follows existing patterns, and is well-tested. Changes correctly thread the parameter through all relevant layers with proper end-to-end testing.

Confidence Score: 5/5

• Safe to merge — the feature is well-scoped, follows existing patterns, is thoroughly tested, and introduces no functional regressions.
• The PR implementation is clean and complete: the new async_httpx_client parameter is correctly threaded through all layers (client → resource manager → async API), preserves the client across get_client() calls, and is comprehensively tested. The code quality is high with minimal changes following established patterns. No functional issues or regressions identified.
• No files require special attention

Sequence Diagram

sequenceDiagram
    participant User
    participant Langfuse
    participant ResourceManager as LangfuseResourceManager
    participant AsyncAPI as AsyncLangfuseAPI

    User->>Langfuse: Langfuse(async_httpx_client=custom_client)
    Langfuse->>ResourceManager: LangfuseResourceManager(..., async_httpx_client=custom_client)
    alt async_httpx_client provided
        ResourceManager->>ResourceManager: self.async_httpx_client = custom_client
    else async_httpx_client is None
        ResourceManager->>ResourceManager: self.async_httpx_client = httpx.AsyncClient(...)
    end
    ResourceManager->>AsyncAPI: AsyncLangfuseAPI(..., httpx_client=self.async_httpx_client)
    AsyncAPI-->>ResourceManager: async_api instance
    ResourceManager-->>Langfuse: resources ready
    Langfuse-->>User: client ready (client.async_api uses custom_client)

    User->>Langfuse: get_client()
    Langfuse->>ResourceManager: _create_client_from_instance(instance)
    ResourceManager-->>Langfuse: Langfuse(..., async_httpx_client=instance.async_httpx_client)
    Langfuse-->>User: client with preserved async_httpx_client

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_{Last reviewed commit: f47f6fb}

[chatgpt-codex-connector]

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[hassiebp]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. More of your lovely PRs please.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve custom async client timeouts

When a caller provides async_httpx_client, this still forwards timeout to AsyncLangfuseAPI, and AsyncLangfuseAPI prefers that explicit timeout over the client’s own timeout config; since Langfuse.__init__ resolves timeout to a concrete value by default, requests from client.async_api are forced to that value instead of using the custom httpx.AsyncClient settings. This makes custom async clients partially ineffective and can cause unexpected request timeouts (for example, long-running endpoints being cut off at the SDK default).

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