AGENT.md: add documentation for agent

[Redent0r]

Add new documentation to assist with rebasing

[Copilot]

Pull request overview

Adds a new AGENT.md checklist-style guide intended to help maintainers rebase the msft-preview fork branch onto newer upstream Kata Containers releases while preserving fork-specific behaviors and CI/test policy.

Changes:

• Introduces a step-by-step rebase setup flow (safety branch, upstream target recording).
• Documents fork behaviors that must survive rebases (runtime-go/runtime-rs resource sizing, CI/test exceptions).
• Adds common conflict hotspots plus focused validation and inspection commands.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[danmihai1]

Great information, thanks for sending it out!

I vote to store it together with other similar and not upstreamed files - e.g., best for me would be in our Wiki pages.

[Redent0r]

Great information, thanks for sending it out!

I vote to store it together with other similar and not upstreamed files - e.g., best for me would be in our Wiki pages.

By having it checked in as an AGENT.md at the root of the repo, an AI agent is able to use it. Eg we can tell the agent "rebase against upstream v.3.31" and it'll take this guide into consideration. I tested this when rebasing from v3.30 to v3.31 and it was pretty much able to do it in one go with no conflicts