Harden Loguru markup handling in test clients

[achamayou]

Summary

• preserve arbitrary existing backslashes when escaping tag-like text for Loguru
• safely embed dynamic request paths, headers, redirect locations, response bodies, and client descriptions in colored log messages
• add a focused unit test that exercises the real flush_info(colors=True) path

Examples of previously unsafe input

Surface	Example input	Previous behavior
Escaped body text	\<invalid>	The old helper added one backslash, producing an even count before <invalid>, so Loguru parsed the unknown tag and raised ValueError.
Request path or redirect Location	/records/<invalid>	The value was interpolated directly into colored markup, so Loguru parsed <invalid> instead of logging it literally.
Request header or client description	<red>spoofed</>	Valid Loguru markup supplied by dynamic data was interpreted, changing the rendered log rather than preserving the input text.
Path or response body ending in a backslash	trailing\	The final backslash could escape the generated </> closing tag; the response workaround avoided the parse issue by adding a visible trailing space.

The hardened paths render each example literally, including the original number of backslashes.

Context

This is defense-in-depth logging hardening split out from #8077. It intentionally does not add COSE, CBOR, or other binary media-type classification or response-body suppression; that minimal COSE-specific behavior remains in #8077.

The broader markup issue was revealed while investigating the failed GitHub Actions job: https://github.com/microsoft/CCF/actions/runs/29526537129/job/87716300085

Testing

• tests/infra/client_logging_test.py
• Black and Ruff on the changed Python files
• Gersemi on CMakeLists.txt

[Copilot]

Pull request overview

This PR hardens the Python test client logging path against Loguru markup parsing errors by escaping tag-like substrings and handling tricky backslash interactions, so dynamically generated request/response data can be safely embedded in colored log messages.

Changes:

• Update Loguru tag escaping to preserve arbitrary existing backslashes and prevent malformed markup sequences.
• Escape dynamic request/response text (paths, headers, redirect locations, bodies) before embedding in colored log lines.
• Add a focused Python unit test and register it with CTest to exercise flush_info(..., colors=True).

Custom instructions used:

• .github/copilot-instructions.md
• .github/instructions/reviewing.instructions.md

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
tests/infra/clients.py	Adds safer escaping helpers and applies them to dynamic text rendered inside Loguru colored messages.
tests/infra/client_logging_test.py	Adds a unit test reproducing Loguru markup parsing scenarios via flush_info(colors=True).
CMakeLists.txt	Registers the new Python unit test with CTest and sets PYTHONPATH for imports.

[achamayou]

Having thought about this, tried other things, contemplated the logs, the loading times in the UI etc I think I want to do #8079 rather than this. I leave it to @eddyashton to make a decision, but I think that we need to do one or the other (or possibly something else, but something!), the current implementation is not sound.