I think it's time to consolidate everything in the AGENTS.md (https://agents.md/):

• Already supported by GitHub Copilot https://github.blog/changelog/2025-08-28-copilot-coding-agent-now-supports-agents-md-custom-instructions/
• Not yet supported by Claude Code (but can be done with a symlink) Feature Request: Support AGENTS.md. anthropics/claude-code#6235

Related files:

• https://github.com/ddev/ddev/blob/main/.github/copilot-instructions.md
• https://github.com/ddev/ddev/blob/main/CLAUDE.md