fix(generators): merge tools from generation_kwargs with component tools

[Rainmemery]

Fixes #12832.

Problem

OpenAIChatGenerator._prepare_api_call and OpenAIResponsesChatGenerator assemble the request payload as {**openai_tools, **generation_kwargs}. Because generation_kwargs is spliced last, a tools key in it replaces the definitions built from the component's own tools instead of being added to them. A caller who passes extra OpenAI tool specs alongside Haystack tools ends up advertising only the former, and the tools it passed as tools are silently dropped.

Fix

Merge the two instead of letting one override the other. For a tool name present in both, the spec given in generation_kwargs wins, mirroring how every other generation_kwargs key already takes precedence.

Applies to:

• OpenAIChatGenerator
• OpenAIResponsesChatGenerator
• AzureOpenAIChatGenerator / AzureOpenAIResponsesChatGenerator (inherited)

Testing

• New regression tests in test/components/generators/chat/test_openai.py and test/components/generators/chat/test_openai_responses.py:
  • tools in generation_kwargs merge with the component's own tools;
  • on name collision the generation_kwargs spec wins.
• Full chat generator suites pass (101 passed).

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⚠️ You currently have 3 open pull requests in this repository (#12837, #12733 and this one). Our review capacity is limited, so please hold off opening more PRs until we've had a chance to review your first 2 open PRs. This helps us give each contribution the attention it deserves. Thank you!

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[sjrl]

Hey @Rainmemery we appreciate the contribution! However, this is something we want to handle internally so I'll be closing this PR.

[Rainmemery]

Understood, thanks for letting me know @sjrl! I will close this PR. The fix itself (merging tools from generation_kwargs with the component tools) is also reproducible independently in OpenAIResponsesChatGenerator, so happy to leave it to the team. Thanks for taking a look.