.NET: [Bug]: CosmosChatHistoryProvider.MessageTtlSeconds = null

[eguzchin-isoftwareiq]

Description

from CosmosChatHistoryProvider.cs

/// <summary>
/// Gets or sets the Time-To-Live (TTL) in seconds for messages.
/// Default is 86400 seconds (24 hours). Set to null to disable TTL.
/// </summary>
public int? MessageTtlSeconds { get; set; } = 86400;

"Set to null to disable TTL." - does not work - ttl = null not allowed
Cosmos db exception -
The input ttl 'null' is invalid. Ensure to provide a nonzero positive integer less than or equal to '2147483647', or '-1' which means never expire."

https://learn.microsoft.com/en-us/cosmos-db/time-to-live

I think your fogot
[JsonProperty ( NullValueHandling = NullValueHandling.Ignore )]

for

[Newtonsoft.Json.JsonProperty("ttl")]
public int? Ttl { get; set; }

Code Sample

Error Messages / Stack Traces

Package Versions

"Microsoft.Agents.AI.CosmosNoSql" Version="1.13.0-preview.260703.1"

.NET Version

NET 8.0

Additional Context

No response

[github-actions]

🤖 Automated triage reproduction notes (agent-authored — trust but verify)

Agent analysis

Bug is in dotnet/src/Microsoft.Agents.AI.CosmosNoSql/CosmosChatHistoryProvider.cs, private class CosmosMessageDocument, line 610-611. The [Newtonsoft.Json.JsonProperty("ttl")] attribute on the int? Ttl property lacks NullValueHandling = NullValueHandling.Ignore, causing "ttl":null to be serialized when MessageTtlSeconds is set to null. Minimal repro: serialize a CosmosMessageDocument with Ttl=null via JsonConvert.SerializeObject and observe "ttl":null in output; Cosmos DB rejects this with "The input ttl 'null' is invalid".

• Failing test: dotnet/tests/Microsoft.Agents.AI.CosmosNoSql.UnitTests/CosmosTtlSerializationTests.cs
• Files examined: dotnet/src/Microsoft.Agents.AI.CosmosNoSql/CosmosChatHistoryProvider.cs, dotnet/tests/Microsoft.Agents.AI.CosmosNoSql.UnitTests/CosmosChatHistoryProviderTests.cs, dotnet/tests/Microsoft.Agents.AI.CosmosNoSql.UnitTests/Microsoft.Agents.AI.CosmosNoSql.UnitTests.csproj
• Tests run: dotnet/tests/Microsoft.Agents.AI.CosmosNoSql.UnitTests/CosmosTtlSerializationTests.cs
• Reported version: 1.13.0-preview.260703.1