fix - Integrate CLS session persistence and restoration for conversation history

[xinyi-gong]

cls related PR: https://github.com/microsoft/copilot-language-server-internal/pull/893

Summary

Integrate CLS (Copilot Language Server) server-side session persistence so that restored conversations can resume with full context instead of relying solely on IDE-side turn history.

Changes

Session restoration protocol:

• Add conversationId and restoreToTurnId fields to ConversationCreateParams for CLS server-side restoration
• Add turnId field to Turn for tracking CLS-assigned turn IDs in the protocol layer
• Update CopilotLanguageServerConnection.createConversation() to accept and forward restoration parameters

Turn ID management:

• User turns are now persisted with turnId = null initially (instead of using workDoneToken as a fake turnId)
• CLS-assigned turnId is set via setUserTurnId() when onChatProgress(begin) arrives
• findOrCreateUserTurn / findOrCreateCopilotTurn use type-aware findTurn(conversation, turnId, Class) to avoid collisions when user and copilot turns share the same turnId

Turn pairing in convertToTurns():

• User and copilot turns are now paired into a single Turn object (request + response) instead of being split into separate Turn objects, matching CLS expectations

Transcript directory configuration:

• Add transcriptDirectory field to CopilotAgentSettings
• Set ~/.copilot/eclipse as transcript directory on startup (matching IntelliJ's ~/.copilot/jb convention)
• Add PlatformUtils.getTranscriptDirectory() and Constants.TRANSCRIPT_SUBDIR

[Copilot]

Pull request overview

This PR integrates Copilot Language Server (CLS) session persistence/restoration into the Eclipse plugin so history-based conversations can be resumed server-side with full context (via conversation/turn restoration parameters), and aligns turn modeling/IDs with CLS expectations.

Changes:

• Adds protocol support for restoration (conversationId, restoreToTurnId) and turn tracking (turnId on Turn).
• Updates persistence to manage CLS-assigned turn IDs (persist user turns with turnId=null, later set from CLS progress begin).
• Configures a consistent transcript directory (~/.copilot/eclipse) for CLS session persistence.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
com.microsoft.copilot.eclipse.ui/src/com/microsoft/copilot/eclipse/ui/preferences/LanguageServerSettingManager.java	Sets agent transcript directory into LSP settings during configuration updates.
com.microsoft.copilot.eclipse.ui/src/com/microsoft/copilot/eclipse/ui/chat/ChatView.java	Sets CLS turnId on persisted user turns; passes restoration parameters when creating history-based conversations.
com.microsoft.copilot.eclipse.ui.test/src/com/microsoft/copilot/eclipse/ui/preferences/LanguageServerSettingManagerTests.java	Updates expected settings to include transcript directory.
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/utils/PlatformUtils.java	Adds helper to compute transcript directory path.
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/persistence/ConversationPersistenceManager.java	Adds type-aware turn lookup and async API to set CLS-assigned user turnId.
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/persistence/ConversationDataFactory.java	Changes turn conversion to pair user+copilot into a single protocol Turn and propagate turnId.
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/lsp/protocol/Turn.java	Adds turnId field, constructor, accessors, and updates equality/hash.
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/lsp/protocol/CopilotAgentSettings.java	Adds transcriptDirectory setting for agent configuration.
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/lsp/protocol/ConversationCreateParams.java	Adds restoration fields (conversationId, restoreToTurnId) to the create payload.
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/lsp/CopilotLanguageServerConnection.java	Adds overload to forward restoration parameters into ConversationCreateParams.
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/Constants.java	Introduces transcript subdirectory constant.