Bug: Tool calls with Object arguments are serialized as string

When using FastFlowLM with OpenCode and Gemma 4 E4B model, I observed frequent tool call failures, by inspecting the log I observed the likely cause to be wrong data serialization

        {
            "content": "",
            "role": "assistant",
            "tool_calls": [
                {
                    "function": {
                        "arguments": "{\"filePath\":\"./src/main/java/my/path/to/JavaClass.java\"}",
                        "name": "read"
                    },
                    "id": "call_1777830235_96",
                    "type": "function"
                },
                {
                    "function": {
                        "arguments": "{\"filePath\":\"./src/main/java/my/path/to/OtherClass.java\"}",
                        "name": "read"
                    },
                    "id": "call_1777830239_97",
                    "type": "function"
                }
            ]
        },

This results in error:

Invalid input for tool read: JSON parsing failed: Text: {{\\\"filePath\\\":\\\"./src/main/java/my/path/to/JavaClass.java\\\\"}}.
Error message: JSON Parse error: Expected '}'

Probably related to https://github.com/FastFlowLM/FastFlowLM/issues/483

No source file or test is named. Start by reviewing issue 483 and reproducing the failure with FastFlowLM, OpenCode, and the Gemma 4 E4B model, then trace tool-call argument serialization. Done means object arguments remain valid JSON for the tool parser and the reported read calls succeed.