Remove Dual JSON Serialization in SaveAndReturnMessageItem

[samsmithnz]

Problem

SaveAndReturnMessageItem() uses both System.Text.Json (for serialization) and Newtonsoft.Json (for deserialization), causing:

• Double deserialization overhead
• Inconsistent behavior between libraries
• Unnecessary dependency on Newtonsoft.Json
• Performance degradation

Current Implementation

Location: SamSmithNZ.Web/Services/BaseServiceApiClient.cs (Lines 83-99)

string jsonInString = JsonSerializer.Serialize(obj); // System.Text.Json
// ...
dynamic jsonObj = Newtonsoft.Json.JsonConvert.DeserializeObject(responseString); // Newtonsoft
result = Newtonsoft.Json.JsonConvert.DeserializeObject<T>(jsonObj?.ToString()); // Double deserialize!

Proposed Solution

string jsonInString = JsonSerializer.Serialize(obj);
StringContent content = new(jsonInString, Encoding.UTF8, "application/json");
HttpResponseMessage response = await _client.PostAsync(url, content);

if (response.IsSuccessStatusCode)
{
    await using Stream stream = await response.Content.ReadAsStreamAsync();
    return await JsonSerializer.DeserializeAsync<T>(stream);
}
return default;

Benefits

• ✅ 50%+ faster deserialization
• ✅ Lower memory allocation
• ✅ Consistent JSON library usage
• ✅ Removes dynamic type usage

Acceptance Criteria

• Method uses only System.Text.Json
• No breaking changes to API contracts
• All integration tests pass
• Performance benchmark shows improvement