VS Code Copilot Chat 400 invalid_request_body: Invalid input[n].id 'thinking_0' (expected 'rs...')

[ekimminau]

Summary

Copilot Chat in VS Code failed with a 400 invalid_request_body error indicating malformed input object IDs in the request payload.

Exact Error

Sorry, your request failed. Please try again.
Client Request Id: 328d73d9-ff78-474c-81e7-2b216032bbeb
GH Request Id: F0D9:9C4A5:2792B94:29627F3:6A26DA23
Reason: Request Failed: 400 {"error":{"message":"Invalid 'input[131].id': 'thinking_0'. Expected an ID that begins with 'rs'.","code":"invalid_request_body"}}

Environment

• OS: Windows 11
• VS Code workspace path: c:/Users/eak/Documents/Documents/Lets_Go
• Date observed: 2026-06-08
• Repo context while using Copilot Chat:
  • ekimminau/Lets_Go
  • branch: admin_context_enhancements

Repro

1. Open an existing Copilot Chat session with accumulated context.
2. Submit a new prompt.
3. Request fails with 400 invalid_request_body and invalid input ID format (thinking_0).

Expected

Request should be accepted and processed by Copilot Chat.

Actual

Backend rejects request body schema due to malformed input ID format.

Additional context

• This appears to be client-side/session-state payload assembly.
• Starting a new chat session may temporarily avoid the failure.
• Local debug logs available at:
  c:/Users/eak/AppData/Roaming/Code/User/workspaceStorage/3a8678e49171e3218fc3d5fc9028b367/GitHub.copilot-chat/debug-logs/4c7041e4-89f5-4800-890d-8b2d3d465b1a

Please use the request IDs for backend/client trace correlation.