Fix tool usage compatibility for OpenRouter models like Meta Llama

[alceasan]

Proposed change

Certain OpenRouter models, particularly Meta Llama versions, have issues with tool usage in Home Assistant's OpenRouter integration. These models often return tool calls in non-standard formats or fail to properly parse tool arguments, leading to errors or non-functional tools.

Root Cause

1. The original implementation assumed tool calls would always be in the proper OpenAI-compatible format
2. Tool argument parsing was fragile and didn't handle edge cases (e.g., bytes, None, nested JSON strings)
3. Models like Meta Llama sometimes embed tool calls as JSON in the response content instead of using proper tool_call fields
4. Tool availability wasn't being carried forward from previous conversation turns

Solution

This PR makes several improvements to ensure robust tool usage:

1. Safer argument decoding: Updated _decode_tool_arguments to handle various input types gracefully with proper fallbacks and logging.

2. Flexible tool call parsing: Modified _transform_response to detect tool calls both in the standard tool_calls field and as JSON embedded in the response content.

3. Dynamic tool discovery: Added logic to scan conversation history and automatically include tools that have been used in previous turns, ensuring continuity in multi-turn conversations.

4. Improved iteration handling: Enhanced the chat iteration loop to better process tool results and maintain tool context across exchanges.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes OpenRouter agent cannot invoke tools #150199

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[home-assistant]

Hi @alceasan

It seems you haven't yet signed a CLA. Please do so here.

Once you do that we will be able to review and accept this pull request.

Thanks!

[home-assistant]

Hey there @joostlek, mind taking a look at this pull request as it has been labeled with an integration (open_router) you are listed as a code owner for? Thanks!

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