feat: Add centralized variables template infrastructure for Ansible playbooks (#105)

[Copilot]

Implements the foundational infrastructure for consolidating Ansible playbook variables into a centralized variables.yml file, following the same pattern as OpenTofu's variables.tfvars.tera.

Implementation

Template & Context

• Template: templates/ansible/variables.yml.tera - Centralized variable definitions with SSH port
• Context: AnsibleVariablesContext - Validates SSH port using existing AnsiblePort validation

Wrapper & Renderer

• Wrapper: AnsibleVariablesTemplate - Renders template with domain TemplateEngine
• Renderer: VariablesTemplateRenderer - Orchestrates template loading, context processing, and file output
• Integration: Hooked into AnsibleTemplateRenderer::render() workflow after firewall playbook rendering

Error Handling

• Added ContextCreationFailed error variant for SSH port validation failures
• Updated both create_firewall_context() and create_variables_context() to use semantically correct error types

Output

Generated variables.yml contains runtime SSH port configuration:

---
# Centralized Ansible Variables
ssh_port: 22
# Future service variables can be added here when needed

Architecture

Follows existing three-layer template pattern:

1. Context Layer - Validates input data (SSH port)
2. Wrapper Layer - Renders Tera template with validated context
3. Renderer Layer - Orchestrates file I/O and template management

Future service variables (MySQL, Tracker, Prometheus, Grafana) can be added to the template without additional Rust infrastructure per service.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Create Variables Template Infrastructure</issue_title>
<issue_description>Parent Epic: #19 - Refactor Ansible Templates to Variables Pattern

Overview

Create the centralized variables.yml.tera template and supporting Rust infrastructure (context, wrapper, renderer) to consolidate Ansible playbook variables into a single file. This establishes the foundation for the variables pattern that will simplify future playbook additions.

Goals

• Variables Template: Create templates/ansible/variables.yml.tera with system configuration variables
• Context Layer: Implement AnsibleVariablesContext with validation
• Wrapper Layer: Implement AnsibleVariablesTemplate for rendering
• Renderer Layer: Implement VariablesTemplateRenderer for orchestration
• Integration: Hook into AnsibleTemplateRenderer::render() workflow
• Test Coverage: Comprehensive unit tests for all components

🏗️ Architecture Requirements

DDD Layer: Infrastructure
Module Path: src/infrastructure/external_tools/ansible/template/
Pattern: Template Wrapper + Context + Renderer (existing pattern)

Time Estimate

2.5 days - Complete vertical slice including implementation, testing, and documentation

Documentation

Full implementation details: docs/issues/19.1-create-variables-template.md

Acceptance Criteria

Template File

• templates/ansible/variables.yml.tera exists with SSH port variable
• Template has correct Tera syntax: {{ ssh_port }}
• YAML linting passes

Implementation

• AnsibleVariablesContext with SSH port validation
• AnsibleVariablesTemplate wrapper implementation
• VariablesTemplateRenderer orchestrator
• Integration into AnsibleTemplateRenderer

Testing

• Unit tests pass: cargo test
• Config tests pass: cargo run --bin e2e-config-tests
• Linters pass: cargo run --bin linter all
• variables.yml generated in build directory

Documentation

• Rustdoc comments for all public types
• Template file includes descriptive comments
• Error types have clear descriptions

Related

• Parent Epic: EPIC: Refactor Ansible Templates to Variables Pattern #19
• Next Task: EPIC: Refactor Ansible Templates to Variables Pattern #19.2 (depends on this task)
• Template System Architecture</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Create Variables Template Infrastructure #105

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[josecelano]

ACK e162cf1