Copilot chat OTel includes system instruction in message JSON

[JamesNK]

Version: 1.111.0-insider (user setup)
Commit: de052c15eaefaceaa5b673081e2834f1cdf193db
Date: 2026-03-05T17:35:21-08:00
Electron: 39.6.0
ElectronBuildId: 13330601
Chromium: 142.0.7444.265
Node.js: 22.22.0
V8: 14.2.231.22-electron.0
OS: Windows_NT x64 10.0.26200

Steps to Reproduce:

1. Enable OpenTelemetry and point it at the standalone Aspire dashboard
2. Use different models (i.e. Opus) to perform operations
3. View traces in Aspire dashboard
4. See System message display twice in some places:

This happens because system instructions are included in the input messages JSON and system instructions JSON. It only needs to be in system instructions JSON

cc @zhichli