CLI violates instructions by ignoring mandatory Microsoft cpp language server (LSP) usage

### Describe the bug

Copilot CLI used grep/glob/raw search even though:

LSP was available
LSP would clearly have been sufficient

The model did not check for LSP availability
The model acknowledged the rule but still violated it.

[lsp_diagnostic_log_2026-05-25_16-06-45.zip](https://github.com/user-attachments/files/28224349/lsp_diagnostic_log_2026-05-25_16-06-45.zip)

Note 1: I'm using the cpp language server (https://github.com/microsoft/cpp-language-server).
Note 2: I've tried with many models (GPT-5 mini, Claude Sonnet 4.6, Claude Opus 4.6), but the output was always the same
### Affected version

GitHub Copilot CLI 1.0.54.

### Steps to reproduce the behavior

[lsp_diagnostic_log_2026-05-25_16-06-45.txt](https://github.com/user-attachments/files/28224382/lsp_diagnostic_log_2026-05-25_16-06-45.txt)

### Expected behavior

Follow instructions from \.github\instructions.md

### Additional context

_No response_

Review .github/instructions.md and the attached diagnostic log, then reproduce the behavior with Copilot CLI 1.0.54 and the Microsoft cpp language server. Done means the CLI follows the stated LSP-use instruction when LSP is available and sufficient; the issue names no implementation file or test.

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