Fix unsupported operation exception in execute tool API

[nathaliellenaa]

Description

There's an issue when executing ReadFromScratchPadTool or WriteToScratchPadTool with empty parameters through the execute tool API. While these tools should support empty parameter execution, they currently throw an exception:

POST /_plugins/_ml/tools/_execute/ReadFromScratchPadTool
{
  "parameters": {}
}

// Exception thrown
{
    "status": 500,
    "error": {
        "type": "NotSerializableExceptionWrapper",
        "reason": "System Error",
        "details": "unsupported_operation_exception: null"
    }
}

The issue is due to the immutable map implementations being passed to these tools. These tools expect to modify the parameters map during execution (reference). When they attempt to call parameters.put() on an immutable map, an UnsupportedOperationException is thrown.

To fix this issue, we need to ensure these tools always receive a mutable map by creating a mutable copy of the parameters before passing them to the tools. This will allow the tools to modify the parameters as needed during execution, even when starting with empty parameters.

Test with current fix:

POST /_plugins/_ml/tools/_execute/ReadFromScratchPadTool
{
  "parameters": {}
}


// Successful response
{
    "inference_results": [
        {
            "output": [
                {
                    "name": "response",
                    "result": "Scratchpad is empty."
                }
            ]
        }
    ]
}

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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[mingshl]

the fix makes sense, because scratch pad string is updated through multiple tool use in one agent execution, so it should be mutable parameters in toolExecution.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.11%. Comparing base (66bcde7) to head (453fbab).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #4325      +/-   ##
============================================
- Coverage     80.14%   80.11%   -0.03%     
+ Complexity    10172    10165       -7     
============================================
  Files           854      854              
  Lines         44219    44219              
  Branches       5113     5113              
============================================
- Hits          35440    35427      -13     
- Misses         6630     6639       +9     
- Partials       2149     2153       +4     

Flag	Coverage Δ
ml-commons	80.11% <100.00%> (-0.03%)	⬇️

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