Set up Cursor Cloud dev environment for NexusOS

[Aidiotic]

Summary

Sets up and verifies the Cursor Cloud development environment for the NexusOS distro-builder codebase (the real product on cursor/nexusos-real-os-06aa; main is only a placeholder README). Adds AGENTS.md documenting durable, non-obvious dev workflow for future agents.

NexusOS is a Bash-based custom Debian distribution builder — there is no dev server or listening port. "Running the app" means running the validator, building a rootfs artifact, or invoking the in-distro nexus-* CLI tools.

Environment

• System toolchain: shellcheck, debootstrap, xz-utils (build/lint deps; python3/make/git/curl/gpg preinstalled).
• Startup update script keeps that toolchain present (idempotent, non-fatal).

Verification (all run in the VM)

• make validate → healthcheck passes (8/8 [OK]).
• shellcheck across *.sh → only expected advisory style/info notices (non-blocking, as in CI).
• sudo NEXUSOS_CI_MINIMAL=1 ./build/rootfs/build-x86_64.sh → produces releases/nexusos-x86_64-rootfs.tar.xz + SHA256SUMS; extracted /etc/os-release shows NAME="NexusOS".
• In-distro tools: nexus-neofetch, nexus-store list/search/install, nexus-settings about, nexus-doctor.
• Hello-world action: installed a package end-to-end via the software center (nexus-store install … → apt install → /var/log/nexus/store.log entry).

nexusos_dev_env_demo.log