shall export: convert declaration files to a standalone script

[SYKhayyat]

Problem

Shall declaration files (modules/*.txt, profiles, etc.) describe what a machine should have, but there is no way to convert them to a standalone script without running shall sync. Users who want to share their setup, use it in CI, or bootstrap a machine before Shall is installed have no path.

Proposed behavior

A new verb: shall export --from-declaration

1. Read the active Shall declarations (modules, profiles, active files)
2. Resolve all packages, services, firewall rules, dotfiles, settings to concrete commands
3. Generate a standalone script in one of three formats:
   • Bash: shell commands
   • Ansible: playbook tasks
   • Nix: NixOS/nix-darwin expression
4. The script should reproduce the machine as declared, without requiring Shall

Design considerations

• Resolution: bare names (e.g., ripgrep) must be resolved to a specific backend before generating script commands. Use the locked backend or fall back to priority.
• Conditional declarations: when os == linux blocks should be handled — generate platform-specific sections or pick the current platform's branch.
• Absent declarations: absent:apt:snap should generate sudo apt-get remove -y snap (or equivalent).
• Options: @version=, @hold, @health= should map to appropriate flags.
• Dotfiles/link: should generate symlink creation or copy commands, with the source path resolved.
• Settings: should generate gsettings set, defaults write, or reg add commands.

Relationship to --from-scan

• --from-scan reads the live machine (ground truth is the running system)
• --from-declaration reads the Shall files (ground truth is the declarations)
• They can complement each other: scan first, export, then manage going forward with Shall

Output example (bash, from a module)

Given:

# modules/tools.txt
apt:ripgrep
cargo:bat
npm:typescript@version=>=5.0.0
absent:snap:firefox

# modules/services.txt
service:nginx @enabled=true

Output:

#!/usr/bin/env bash
# Generated by shall export --from-declaration --format bash

# Packages (apt)
sudo apt-get install -y ripgrep

# Packages (cargo)
cargo install bat

# Packages (npm)
sudo npm install -g 'typescript@>=5.0.0'

# Removals
sudo apt-get remove -y snap firefox || true

# Services
sudo systemctl enable --now nginx