[Docs] how to register an agent harness (#2521)
* docs: how to register an agent harness
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
* Apply suggestions from code review
Co-authored-by: Daniel van Strien <davanstrien@users.noreply.github.com>
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Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Co-authored-by: Daniel van Strien <davanstrien@users.noreply.github.com>
