[dfedoryshchev]

ToContentBlock on a FunctionResultContent whose Result is not an AIContent builds the text block from the whole FunctionResultContent instead of from Result, so the text is a JSON object with $type, result and callId in it rather than the tool's output.

Through SampleAsync(IEnumerable<ChatMessage>, ...) / AsSamplingChatClient() with UseFunctionInvocation(), a local tool's result reaches the client as {"$type":"functionResult","result":"Weather in Paris: ...","callId":"call_weather_123"}, and that is what the client's model reads. That path is [Obsolete] with the rest of sampling, but ToContentBlock itself is public and not obsolete, so any caller converting a function result hits the same thing.

The fix serializes resultContent.Result, the same way AIFunctionMcpServerTool turns a non-content return value into text. StructuredContent was already taken from Result, so the two now agree.

EndToEnd_SamplingWithTools_... already goes through this path, but it only asserts that the text contains "Weather in Paris: sunny", which the wrapped JSON also does. I added one DoesNotContain("callId") line there, plus unit tests for a string result, a JsonElement result and an AIContent result (the last one is unchanged behaviour).

One thing you may want differently: a string result that comes through as a JsonElement still ends up quoted ("Weather in Paris: ..."), the same as a tool returning a JsonElement string today. I kept it consistent with that path rather than unwrapping strings here, but happy to change it if you prefer.

Tests pass on net10.0, net9.0, net8.0 and net472.