update .openhands instructions

[rbren]

End-user friendly description of the problem this fixes or functionality that this introduces

• Include this change in the Release Notes. If checked, you must provide an end-user friendly description for your change below
  CHANGELOG: Documented the new .openhands directory for customizing prompts for individual repositories

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Give a summary of what the PR does, explaining any non-trivial design decisions

• Makes it easier to write a generic microagent (no YAML metadata at the top of the file == always trigger)
• Puts the generic instructions into the system prompt (this seems to have been missing?)
• Documents the new pattern

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Link of any specific issues this addresses

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:02072eb-nikolaik   --name openhands-app-02072eb   docker.all-hands.dev/all-hands-ai/openhands:02072eb

[tofarr]

🍰

[xingyaoww]

As a side note, i think it probably makes more sense to add repository instructions in the first USER message rather than system message, which is typically used to define the behavior of LLM?

[enyst]

Since this was deleted, will the resolver find it? It doesn't seem so

OpenHands/openhands/resolver/resolve_issue.py

Line 406 in 32ee500

openhands_instructions_path = os.path.join(repo_dir, '.openhands_instructions')

[xingyaoww]

Maybe we should create a new issue for it

[enyst]

Done -ish, here, it's expressed as a quick prompt for oh #5830 , but its fix was to hardcode the new path... That can't be what we want for a microagent