Add JSON output to `validate` command (12.10)

[josecelano]

Overview

Add JSON output format support to the validate command (roadmap task 12.10). This is part of Phase 2 of the JSON output epic (#348), which aims to implement JSON output for all remaining commands so that JSON can eventually become the default output format.

The validate command currently only outputs human-readable text progress messages and a validation summary. This task adds a machine-readable JSON alternative that automation workflows, CI/CD pipelines, and AI agents can parse programmatically.

Key characteristic: The validate command takes an --env-file <PATH> argument and performs validation without creating any deployment state. Its output reflects configuration properties extracted from the file — environment name, provider, and enabled feature flags (Prometheus, Grafana, HTTPS, backup). There is no domain Environment state object involved — the DTO is built directly from ValidationResult.

Specification

See detailed specification: docs/issues/390-add-json-output-to-validate-command.md

🏗️ Architecture Requirements

DDD Layer: Presentation
Module Path: src/presentation/cli/views/commands/validate/
Pattern: Strategy Pattern for rendering (same as provision, create, show, run, list, configure, release, test, destroy)

Module Structure Requirements

• Follow the existing view module structure established in destroy/ (has view_data/)
• ValidateDetailsData is a plain presentation DTO deriving Serialize, PartialEq (not Deserialize) with a named constructor from_result(&Path, &ValidationResult)
• JsonView::render() returns String — serialization errors handled inline via unwrap_or_else
• TextView::render() formats the same data as human-readable text and also returns String

Architectural Constraints

• No business logic in presentation layer — only rendering
• Error handling follows project conventions
• Output must go through UserOutput methods — never println! or eprintln! directly
• The ValidateDetailsData DTO must derive serde::Serialize (output-only — no Deserialize needed)

Anti-Patterns to Avoid

• ❌ Mixing rendering concerns in the controller
• ❌ Adding business logic to view structs
• ❌ Using println!/eprintln! instead of UserOutput

Implementation Plan

Phase 1: View Module

• Create src/presentation/cli/views/commands/validate/mod.rs
• Implement ValidateDetailsData DTO with from_result() constructor in view_data/validate_details.rs
• Implement JsonView::render() in views/json_view.rs
• Implement TextView::render() in views/text_view.rs
• Register validate in src/presentation/cli/views/commands/mod.rs

Phase 2: Controller + Router

• Add output_format: OutputFormat parameter to ValidateCommandController::execute()
• Refactor complete_workflow() to accept and dispatch on output_format
• Update router to pass output_format from context to controller

Phase 3: Tests + Manual Verification + Docs

• Unit tests for JsonView::render()
• Unit tests for TextView::render()
• Manual verification: run cargo run -- validate --env-file envs/lxd-local-example.json and confirm text output is unchanged
• Manual verification: run cargo run -- validate --env-file envs/lxd-local-example.json --output-format json 2>/dev/null and confirm JSON output matches spec
• Update docs/user-guide/commands/validate.md with JSON output examples

Acceptance Criteria

Note for Contributors: These criteria define what the PR reviewer will check. Use this as your pre-review checklist before submitting the PR to minimize back-and-forth iterations.

Quality Checks:

• Pre-commit checks pass: ./scripts/pre-commit.sh

Task-Specific Criteria:

• validate --output-format json outputs valid JSON with all expected fields
• validate --output-format text (default) produces human-readable output identical to current output
• Unit tests cover both view renderers
• Documentation updated with JSON output examples

Related

• Parent: EPIC: Add JSON output format support #348 (EPIC: Add JSON output format support)
• Roadmap: section 12.10
• Reference implementation (destroy): src/presentation/cli/views/commands/destroy/
• Reference implementation (test): src/presentation/cli/views/commands/test/