Fix 400 Bad Request when restoring conversation from persistence

[xinyi-gong]

fix #131

When restoring a history-based conversation, the first request to the LLM intermittently fails with a 400 Bad Request error. Two issues were found:

1. Assistant response duplicated as user message

In ConversationDataFactory.convertToTurns(), the assistant's response text was incorrectly assigned to the request field of the Turn object, causing the LLM's previous reply to appear as a role: "user" message in the history.

Fix: Use an empty string for the request field on assistant turns, keeping the response text only in the response field.

2. New user message not appended at the end

In CopilotLanguageServerConnection.createConversation(), historical turns were appended after the current user message (addAll(turns)). Since ConversationCreateParams places the current user message as the first turn, this resulted in the messages array ending with an assistant role message. Claude API requires the last message to be role: "user", causing a 400 error.

Fix: Insert historical turns before the current user message using addAll(0, turns).

[Copilot]

Pull request overview

Fixes intermittent 400 Bad Request when restoring a history-based chat conversation by correcting how persisted turns are reconstructed and ordered before sending the first request to the language server/LLM.

Changes:

• Fix persisted assistant turns so the assistant response is no longer duplicated into the Turn.request (user) field.
• Insert historical turns before the current user message when creating a history-based conversation, ensuring the last message is the new user request.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/persistence/ConversationDataFactory.java	Adjusts persisted turn conversion so assistant turns don’t populate the user request content.
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/lsp/CopilotLanguageServerConnection.java	Reorders turn insertion so historical turns precede the current user message to satisfy model API constraints.