Resend all messages when WebSocket's previous response id does not match

[chrmarti]

#298236

[Copilot]

Pull request overview

This PR improves Responses API WebSocket request construction by using the active WebSocket connection’s last completed response.id as the authoritative stateful marker, and falling back to sending full in-scope message history when that marker isn’t present in the current message list (avoiding invalid previous_response_id resumes). This aligns request slicing with WebSocket connection state for CAPI WebSocket support (#298236).

Changes:

• Add getStatefulMarker(conversationId) to IChatWebSocketManager and implement it for real and null managers.
• Update Responses API request body creation to use the WebSocket manager’s marker when on WebSocket transport, and only resume (previous_response_id + post-marker slicing) when that marker exists in the current messages.
• Extend unit tests to cover the “stale WebSocket marker” case and ensure WebSocket request slicing uses the connection marker.

Show a summary per file

File	Description
extensions/copilot/src/platform/test/node/services.ts	Registers IChatWebSocketManager in platform test services so WebSocket-aware code paths can resolve the service.
extensions/copilot/src/platform/networking/node/chatWebSocketManager.ts	Extends the manager interface and implementations to expose the active connection’s statefulMarker.
extensions/copilot/src/platform/endpoint/node/test/responsesApi.spec.ts	Adds/updates tests to validate WebSocket marker-based slicing and the resend-all behavior when the marker is stale.
extensions/copilot/src/platform/endpoint/node/responsesApi.ts	Uses WebSocket connection marker when applicable; omits previous_response_id and avoids slicing if the marker isn’t found in messages.
extensions/copilot/src/platform/endpoint/common/statefulMarkerContainer.tsx	Adds getIndexOfStatefulMarker helper to locate a specific marker in message history.

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 0