Why an already added Microsoft.SemanticKernel.FunctionResultContent history item is altered by future interactions?

[aprecup14]

Hi!

Specs

• .NET Semantic Kernel 1.65.0`
• Microsoft.SemanticKernel.Connectors.Ollama 1.65.0-alpha
• Ollama model: gpt-oss:20b

What I have
A LightsPlugin like the docs example. I add the plugin to the kernel, create a history object with a simple system prompt ("You are a helpful assistant"). User messages are passed to GetChatMessageContentAsync (as part of the history) with FunctionChoiceBehavior.Auto() and the kernel for tool support.

Repro steps

1. User: "what's the status of the lights" → kernel calls the get_lights function and returns the result.
2. User: "turn on the porch light" → kernel calls the toggle_light function; porch light successfully turns on.

Problem
After step 2, the recorded history entry for the step 1 function call (Microsoft.SemanticKernel.FunctionResultContent) is altered — it now shows the porch light as "on", even though get_lights ran before the toggle instruction. I confirmed this both in the debugger and by inspecting HTTP traffic (mitmproxy). Attached are raw request exports for step 1 and step 2 showing the altered history:

Step 1 request

POST /api/chat HTTP/1.1
Host: localhost:11434
Content-Type: application/json; charset=utf-8
Content-Length: 1535

{"model":"gpt-oss:20b","messages":[{"role":"system","content":"You are a helpful assistant. Be concise and polite."},{"role":"user","content":"What's the status of the lights?"},{"role":"assistant","content":"","tool_calls":[{"function":{"index":null,"name":"Lights_get_lights","arguments":{}}}]},{"role":"tool","content":"{\"CallId\":\"a8a9cd39\",\"Result\":[{\"id\":1,\"name\":\"Table Lamp\",\"is_on\":false},{\"id\":2,\"name\":\"Porch light\",\"is_on\":false},{\"id\":3,\"name\":\"Chandelier\",\"is_on\":true}]}"}],"options":{},"stream":false,"tools":[{"type":"function","function":{"name":"Lights_get_lights","description":"Gets a list of lights and their current state","parameters":{"type":"object","properties":{},"required":null}}},{"type":"function","function":{"name":"Lights_change_state","description":"Changes the state of the light","parameters":{"type":"object","properties":{"id":{"type":"integer","description":null,"enum":null},"isOn":{"type":"boolean","description":"Whether the light should be toggled on or of","enum":null}},"required":["id","isOn"]}}},{"type":"function","function":{"name":"Weather_get_weather","description":"Gets the current weather.","parameters":{"type":"object","properties":{},"required":null}}},{"type":"function","function":{"name":"SummarizePlugin_Function_4e11ebdca1814db7aef3bb86def094dd","description":"Generic function, unknown purpose","parameters":{"type":"object","properties":{"input":{"type":"string","description":null,"enum":null}},"required":["input"]}}}],"CustomHeaders":{}}

Step 2 request (after the porch light has been turned on)

POST /api/chat HTTP/1.1
Host: localhost:11434
Content-Type: application/json; charset=utf-8
Content-Length: 2133

{"model":"gpt-oss:20b","messages":[{"role":"system","content":"You are a helpful assistant. Be concise and polite."},{"role":"user","content":"What's the status of the lights?"},{"role":"assistant","content":"","tool_calls":[{"function":{"index":null,"name":"Lights_get_lights","arguments":{}}}]},{"role":"tool","content":"{\"CallId\":\"a8a9cd39\",\"Result\":[{\"id\":1,\"name\":\"Table Lamp\",\"is_on\":false},{\"id\":2,\"name\":\"Porch light\",\"is_on\":true},{\"id\":3,\"name\":\"Chandelier\",\"is_on\":true}]}"},{"role":"assistant","content":"Here’s the current status of the lights:\n\n| ID | Name         | On/Off |\n|----|--------------|--------|\n| 1  | Table Lamp   | Off    |\n| 2  | Porch light  | Off    |\n| 3  | Chandelier   | On     |\n\nLet me know if you’d like to toggle any of them!"},{"role":"user","content":"Turn the porch light on"},{"role":"assistant","content":"","tool_calls":[{"function":{"index":null,"name":"Lights_change_state","arguments":{"id":2,"isOn":true}}}]},{"role":"tool","content":"{\"CallId\":\"197da703\",\"Result\":{\"id\":2,\"name\":\"Porch light\",\"is_on\":true}}"}],"options":{},"stream":false,"tools":[{"type":"function","function":{"name":"Lights_get_lights","description":"Gets a list of lights and their current state","parameters":{"type":"object","properties":{},"required":null}}},{"type":"function","function":{"name":"Lights_change_state","description":"Changes the state of the light","parameters":{"type":"object","properties":{"id":{"type":"integer","description":null,"enum":null},"isOn":{"type":"boolean","description":"Whether the light should be toggled on or of","enum":null}},"required":["id","isOn"]}}},{"type":"function","function":{"name":"Weather_get_weather","description":"Gets the current weather.","parameters":{"type":"object","properties":{},"required":null}}},{"type":"function","function":{"name":"SummarizePlugin_Function_4e11ebdca1814db7aef3bb86def094dd","description":"Generic function, unknown purpose","parameters":{"type":"object","properties":{"input":{"type":"string","description":null,"enum":null}},"required":["input"]}}}],"CustomHeaders":{}}

Question
Is this expected behavior (i.e., are FunctionResultContent history items mutated by later actions), or is something in my usage causing the earlier history item to be updated?

Thanks!

[Samielakkad]

This is reference aliasing, not Semantic Kernel intentionally rewriting history.

FunctionResultContent.Result is stored as an object reference. Its constructor assigns the supplied result directly; it does not serialize or deep-clone it:

https://github.com/microsoft/semantic-kernel/blob/main/dotnet/src/SemanticKernel.Abstractions/Contents/FunctionResultContent.cs

If get_lights returns the plugin's live List<Light> (or objects from that list), the history item and the plugin state point at the same mutable Light instances. toggle_light later changes PorchLight.IsOn. When the earlier FunctionResultContent is serialized for the next request, it observes the updated object and emits true.

Return a snapshot from read functions instead of the live state. For example:

[KernelFunction("get_lights")]
public IReadOnlyList<LightSnapshot> GetLights() =>
    _lights.Select(light => new LightSnapshot(
        light.Id,
        light.Name,
        light.IsOn
    )).ToArray();

public sealed record LightSnapshot(int Id, string Name, bool IsOn);

The same rule should apply to mutation results:

return new LightSnapshot(light.Id, light.Name, light.IsOn);

Using immutable records is preferable to returning the domain entities. A JSON round-trip/deep copy would also break the reference, but a dedicated snapshot DTO is cheaper and makes the history semantics explicit.

A minimal confirmation is:

var first = GetLights();
ChangeState(2, true);

Assert.False(first.Single(x => x.Id == 2).IsOn);

That assertion will fail when GetLights() exposes the live objects and pass when it returns snapshots. The history should represent what the tool returned at invocation time, so snapshotting at the plugin boundary is the correct fix.