chat: fix system prompt accumulation across conversation turns

[BenjaminMichaelis]

Problem

In both GetChatCompletionStream and GetChatCompletionCore, the system prompt was added as a ResponseItem.CreateSystemMessageItem(...) in the input items list on every call. When previous_response_id is used on follow-up turns, OpenAI already holds the full conversation server-side — including the system message from turn 1. Every subsequent turn (and every tool-call leg) was adding it again, causing the system prompt to accumulate in context.

Fix

Move the system prompt to ResponseCreationOptions.Instructions in CreateResponseOptionsAsync, and remove the system message item from both call sites.

Per the Azure OpenAI Responses API docs:

"When using along with previous_response_id, the instructions from a previous response will not be carried over to the next response. This makes it simple to swap out system (or developer) messages in new responses."

Instructions is stateless across turns by design — applied fresh each call, never accumulated.

Changes

• CreateResponseOptionsAsync: Added string? systemPrompt parameter; sets options.Instructions from it (falling back to _Options.SystemPrompt). Changed from static to instance method to access _Options.
• GetChatCompletionCore: Removed systemPrompt parameter; input list is always [ResponseItem.CreateUserMessageItem(prompt)].
• GetChatCompletionStream: Same simplification — no system message item in input list.
• GetChatCompletion: Passes systemPrompt to CreateResponseOptionsAsync instead of downstream to GetChatCompletionCore.

[Copilot]

Pull request overview

This PR updates the Azure OpenAI Responses API integration to prevent the system prompt from being repeatedly appended to the conversation when using previous_response_id, by moving the system prompt from input message items into ResponseCreationOptions.Instructions (applied per-call and not accumulated across turns).

Changes:

• Set the system prompt via ResponseCreationOptions.Instructions in CreateResponseOptionsAsync (with optional override).
• Remove ResponseItem.CreateSystemMessageItem(...) from both non-streaming and streaming request item lists.
• Simplify GetChatCompletionCore to accept only the user prompt + response options.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

[BenjaminMichaelis]

@copilot resolve the merge conflicts in this pull request

[BenjaminMichaelis]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved in commit f6d976c by merging origin/main into this branch and fixing the AIChatService.cs conflict so both the system-prompt Instructions behavior and the latest MCP tool-call flow are preserved.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• api.hcaptcha.com
  • Triggering command: /home/REDACTED/work/EssentialCSharp.Web/EssentialCSharp.Web/EssentialCSharp.Web.Tests/bin/Release/net10.0/EssentialCSharp.Web.Tests /home/REDACTED/work/EssentialCSharp.Web/EssentialCSharp.Web/EssentialCSharp.Web.Tests/bin/Release/net10.0/EssentialCSharp.Web.Tests --server dotnettestcli --dotnet-test-pipe /tmp/477bf40cf99242e98a28b32bfb6e16ac (dns block)
• api.pwnedpasswords.com
  • Triggering command: /home/REDACTED/work/EssentialCSharp.Web/EssentialCSharp.Web/EssentialCSharp.Web.Tests/bin/Release/net10.0/EssentialCSharp.Web.Tests /home/REDACTED/work/EssentialCSharp.Web/EssentialCSharp.Web/EssentialCSharp.Web.Tests/bin/Release/net10.0/EssentialCSharp.Web.Tests --server dotnettestcli --dotnet-test-pipe /tmp/477bf40cf99242e98a28b32bfb6e16ac (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

[Copilot]

@copilot resolve the merge conflicts in this pull request

Handled in commit f6d976c. I re-checked this branch against origin/main and there are no remaining merge conflicts.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.