Add AGENTS guide for coding agents

AGENTS.md

@@ -0,0 +1,166 @@
+# AGENTS.md
+
+Guide for coding agents in this repository.
+Project type: Ansible infrastructure + managed dotfiles.
+
+## Repository map
+- Entry playbook: `ansible/site.yml`
+- Inventory: `ansible/inventory/hosts.yml`
+- Group vars: `ansible/inventory/group_vars/*.yml`
+- Host vars: `ansible/inventory/host_vars/*.yml`
+- Roles: `ansible/roles/*/tasks/main.yml`
+- Dotfiles source: `dotfiles/`
+- Ansible config: `ansible.cfg`
+
+`ansible.cfg` defaults in use:
+- `inventory = ansible/inventory/hosts.yml`
+- `roles_path = ansible/roles`
+- `host_key_checking = False`
+- `retry_files_enabled = False`
+
+## Cursor / Copilot rules status
+Checked and not found:
+- `.cursorrules`
+- `.cursor/rules/`
+- `.github/copilot-instructions.md`
+
+If these files are added later, treat them as higher-priority local instructions.
+
+## Dependencies
+Required:
+- Python 3
+- Ansible
+- Access to target hosts (local or SSH, depending on inventory)
+
+Install baseline:
+```bash
+python3 -m pip install ansible
+```
+
+Optional quality tools:
+```bash
+python3 -m pip install ansible-lint yamllint
+```
+
+## Build / lint / test commands
+There is no compile/build artifact in this repo.
+Use syntax checks, dry-runs, and linting as validation.
+
+Main run:
+```bash
+ansible-playbook ansible/site.yml
+```
+
+Run only one host:
+```bash
+ansible-playbook ansible/site.yml --limit ikaros
+```
+
+Dry-run with diff:
+```bash
+ansible-playbook ansible/site.yml --check --diff
+```
+
+Inventory sanity checks:
+```bash
+ansible-inventory --graph
+ansible-inventory --list
+```
+
+Linting (if installed):
+```bash
+ansible-lint ansible/site.yml
+ansible-lint ansible/roles
+yamllint ansible/
+```
+
+## Single-test equivalents (important)
+No dedicated test harness (pytest/molecule) exists yet.
+Use these targeted commands as "single test" workflows.
+
+Syntax-check one playbook:
+```bash
+ansible-playbook ansible/site.yml --syntax-check
+```
+
+Test one host in dry-run mode:
+```bash
+ansible-playbook ansible/site.yml --limit nymph --check --diff
+```
+
+Start at one task:
+```bash
+ansible-playbook ansible/site.yml --start-at-task "Copy .bashrc" --limit ikaros
+```
+
+Run one tag subset (requires tagged tasks):
+```bash
+ansible-playbook ansible/site.yml --tags dotfiles --limit ikaros
+```
+
+## Code style guidelines
+
+### General principles
+- Keep changes idempotent and declarative.
+- Preserve layering: `common -> OS -> profile -> host`.
+- Avoid unrelated refactors; keep edits minimal and local.
+
+### Ansible modules, imports, and structure
+- Use FQCN module names (`ansible.builtin.copy`, `community.general.xbps`).
+- Prefer modules over raw `shell`/`command`.
+- Use `import_tasks`/`include_tasks` when role task files grow.
+- Keep `site.yml` orchestration-focused; implementation lives in roles.
+- Keep role scope narrow (packages vs services vs dotfiles).
+
+### Formatting
+- Start YAML files with `---`.
+- Use 2-space indentation; never tabs in YAML.
+- Quote modes as strings: `"0644"`, `"0755"`, `"0600"`.
+- Keep long Jinja expressions multiline and readable.
+- No trailing whitespace.
+
+### Variables and types
+- Use `snake_case` variable names.
+- Keep names semantically scoped (`common_packages`, `profile_packages`, `host_packages`).
+- Use true YAML types: lists for lists, booleans as `true`/`false`.
+- Use `default([])` / `default({})` for optional vars.
+- Keep paths consistent, usually templated from `{{ user_home }}`.
+- Put global defaults in `group_vars/all.yml`; specialize in group/host vars.
+
+### Naming conventions
+- Roles: lowercase with underscores.
+- Tasks: imperative, explicit outcome (`Install packages on Void Linux`).
+- Inventory group and var file names must stay aligned.
+- Host var files should match hostnames exactly.
+
+### Error handling and safety
+- Guard OS/profile-specific actions with `when`.
+- For `command`/`shell`, set `changed_when`/`failed_when` where needed.
+- Do not suppress failures without clear justification.
+- Validate risky changes with `--check --diff` before real apply.
+- Avoid destructive user-file operations unless explicitly required.
+
+### Shell and dotfiles
+- Prefer POSIX `sh` unless Bash features are required.
+- If Bash is required, use `#!/usr/bin/env bash`.
+- Quote expansions (`"$var"`) unless intentional word splitting is required.
+- Keep automation-invoked scripts non-interactive.
+
+## Agent operating expectations
+- Never commit or expose data from `secrets/`.
+- Do not modify unrelated files.
+- Keep docs (`README.md`, `AGENTS.md`) current when workflows change.
+- If adding new task domains, add tags to improve targeted runs.
+
+## Pre-merge checklist
+```bash
+ansible-playbook ansible/site.yml --syntax-check
+ansible-playbook ansible/site.yml --check --diff --limit <host>
+ansible-inventory --graph
+```
+
+If lint tools are installed:
+```bash
+ansible-lint ansible/site.yml
+yamllint ansible/
+```