Aitor Nain Mendoza Vallejo (naindev)
Madrid, Spain • Full Stack Software Architect • CTO at Contrast3D x NainDev

I am a full stack software architect with a backend focus. I specialize in critical systems, trustworthy AI, and deterministic conformance: architectures that validate products of any domain against explicit, versioned specifications, starting with 3D assets.

I deliver the complete product (data model, backend, and frontend) and integrate AI through human-in-the-loop MCP tooling, on Open Core architectures with clean code and immutable contracts.

What I bring to a team or client:

• Python and .NET at the same level. Python (FastAPI, Pydantic v2) for AI, validation, data, and 3D. .NET (ASP.NET Core) for business APIs and Microsoft-based clients.
• End-to-end ownership. PostgreSQL or SQL Server schemas, async APIs, accessible Vue 3 frontends (WCAG 2.2 AA), CI/CD, and deployment on Linux VPS or Azure.
• Verifiable delivery. Spec-driven development, property-based testing, and traceability from each requirement to the test that proves it.
• Legacy modernization. Maintenance, security hardening and incremental modernization of critical .NET Framework backends without stopping the business.

My main work is not public. The first two systems I lead under my NainDev brand, outside working hours; the third is my full-time role as a .NET developer in the insurance sector. They are listed in order of focus and described by architecture and stack only:

• Multi-Domain Deterministic Conformance Chassis (Open Core): Python 3.12 (uv monorepo), FastAPI, Pydantic v2, PostgreSQL, Model Context Protocol (MCP), pytest & Hypothesis, Docker, self-hosted CI.

  • Architecture: A domain-agnostic conformance chassis that receives an artefact, identifies what it is, measures facts about it, proposes the objectives and profile that apply, validates it, directs its fail-closed correction, and emits a verdict that is reproducible byte-for-byte. Each market domain plugs in as a versioned profile from a frozen, persisted catalogue; the catalogue version is recorded in every verdict.
  • First profile, in production: Real-time 3D assets (glTF/GLB). Binary stream parsing and byte-level container validation (IEEE-754 little-endian chunk extraction), exact computational geometry invariants (2D UV winding, polygon clipping, watertight manifold verification, differential texel density scaling), and a validate → repair → revalidate loop.
  • Next profile, specified: Tabular fiscal documents (invoice arithmetic, mandatory legal fields, and tax ID check-digit algorithms), which proves the same engine works outside 3D.
  • Delivery: Reproducible dual-contract audit reports (canonical JSON + human-readable Markdown), an HTTP service with OpenAPI, PostgreSQL persistence for stateful validation sessions, and stdio MCP tooling so AI agents run validations under human oversight.

• High-Concurrency Multi-Tenant Operations & Commercial Platform: Python 3.12, FastAPI, PostgreSQL, async SQLAlchemy, Alembic, Vue 3, TypeScript, Pinia, Tailwind CSS, Web Push (VAPID), Docker.

  • Core capabilities: Zero-data-loss collaboration using entity version tracking and field-level merge resolution on HTTP 409 conflicts. Data integrity enforced by PostgreSQL primitives (citext, partial unique indexes, and atomic activity_events audit logging within single transactions). Accessible frontend (WCAG 2.2 AA, TipTap rich text, interactive 3D model viewers) and near-zero compute cost on self-hosted environments backed by local CI runner fleets.

• Insurance-Sector Backend & Legacy .NET Modernization (full-time role): C#, .NET Framework, ASP.NET MVC 5, ASP.NET Web API 2, SQL Server, Dapper, Azure Storage, layered architecture.

  • Core capabilities: RESTful APIs for insurance policy management and risk scoring. Maintenance, security hardening, and incremental modernization of mission-critical business backends. Integration layer orchestrating multiple third-party enterprise providers (payment gateways, digital signature APIs, financial scoring services, cloud storage, and automated transactional document generation).

Open-source projects with source code and automated tests. Live demos where available:

+-----------------------------------------------------------------------------------+
|                                  Presentation                                     |
|   Vue 3 + TypeScript (WCAG 2.2 AA) | Astro | Three.js / WebGL 3D viewers          |
+-----------------------------------------+-----------------------------------------+
                                          |  OpenAPI contracts
+-----------------------------------------v-----------------------------------------+
|                                  Application                                      |
|   FastAPI | ASP.NET Core | MCP tools with human-in-the-loop approval              |
+-----------------------------------------+-----------------------------------------+
                                          |
+-----------------------------------------v-----------------------------------------+
|                                    Domain                                         |
|   Deterministic invariants | Immutable contracts (Pydantic v2 / C# records)       |
+-----------------------------------------+-----------------------------------------+
                                          |
+-----------------------------------------v-----------------------------------------+
|                                 Infrastructure                                    |
|   PostgreSQL | SQL Server | Docker | GitHub Actions | Linux VPS | Azure           |
+-----------------------------------------------------------------------------------+

1. Spec-driven development: Every change starts in a specification (charter, EARS requirements, architecture with Mermaid diagrams, data model, ADRs, and traceability), never directly in code.
2. Nothing claimed without a test: Business rules and geometric invariants are covered by automated and property-based tests. A requirement without a test is not done.
3. Strict layer boundaries: The frontend presents and the backend decides. Business logic lives in the domain and services; data access lives only in repositories.
4. Immutable public contracts: APIs, schemas, and reports are versioned contracts. Breaking changes are explicit and documented.
5. Human-in-the-loop AI: AI agents act through MCP tools with deterministic checks and human approval, and fail closed when uncertain.
6. Open Core and cost awareness: Free and open-source tooling for demos and proofs of concept; production costs are evaluated against each product's business model.

Open to part-time, remote projects in software architecture, backend engineering, legacy .NET modernization, and deterministic conformance systems:

• Portfolio: www.naindev.com
• Email: contact@naindev.com
• LinkedIn: Aitor Nain Mendoza Vallejo