Normalize CallToolResult.StructuredContent to JsonElement?

[Copilot]

• Investigate JsonElement vs JsonNode usage across the codebase and validate this is the right change
• Change CallToolResult.StructuredContent from JsonNode? to JsonElement?
• Update AIFunctionMcpServerTool.CreateStructuredResponse to return JsonElement? instead of JsonNode?
• Refactor CreateStructuredResponse switch to target JsonElement? directly, only using JsonNode for the wrapping path
• Use JsonSerializer.SerializeToElement instead of .Deserialize() for JsonNode/JsonObject → JsonElement conversion
• Update AIFunctionMcpServerTool.ConvertAIContentEnumerableToCallToolResult parameter type
• Update test files: CallToolResultTests.cs, UnknownPropertiesTests.cs, McpClientToolTests.cs, McpServerToolTests.cs
• Build and run tests to verify changes (all 1824+283 tests pass across net8.0/net9.0/net10.0)
• Code review and security scan (0 CodeQL alerts)

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[jeffhandley]

This is looking good to me. @copilot Can you confirm for me please any remaining JsonNode exposures in the public API surface after these changes?

[Copilot]

This is looking good to me. @copilot Can you confirm for me please any remaining JsonNode exposures in the public API surface after these changes?

After these changes, the only remaining JsonNode exposures in the public API surface are the three JSON-RPC message wrapper properties:

• JsonRpcRequest.Params (JsonNode?)
• JsonRpcNotification.Params (JsonNode?)
• JsonRpcResponse.Result (required JsonNode?)

These are intentionally JsonNode since they represent the raw, mutable RPC-level payloads before deserialization into typed protocol DTOs. All protocol-level DTO properties now consistently use JsonElement.

[Copilot]

This is looking good to me. @copilot Can you confirm for me please any remaining JsonNode exposures in the public API surface after these changes?

After these changes, the only remaining JsonNode exposures in the public API surface are the three JSON-RPC message wrapper properties:

• JsonRpcRequest.Params (JsonNode?)
• JsonRpcNotification.Params (JsonNode?)
• JsonRpcResponse.Result (required JsonNode?)

These are intentionally JsonNode since they represent the raw, mutable RPC-level payloads before deserialization into typed protocol DTOs. All protocol-level DTO properties now consistently use JsonElement.

[halter73]

This does feel a bit more consistent with Tool.OutputSchema which I think is good. I don't claim to be an authority on this though.