Arnaldo Sepulveda

Writing

Engineering write-ups on building, evaluating, debugging, and operating AI systems. Local essays appear alongside selected work from the Keystone blog.

Published
August 2026 · Keystone blog

The Six Substrate Dimensions

A proposed test for what might belong in the substrate: if you replace the agent, framework, or provider and the property is still necessary, it may be a substrate candidate. The piece examines six candidate dimensions as research hypotheses rather than an established ontology.

August 2026 · Keystone blog

The Protocol Between Agents Is the Protocol Between Teams

Reflections from 12+ years working with enterprise contact-center systems, and a hypothesis about how interface changes, organizational boundaries, and accumulated governance mechanisms may reappear in multi-agent AI.

July 2026 · Keystone blog

Causal Decomposition Under Suspended Judgment: Two Cases from Keystone

Two cases in diagnosing governed AI failures at the mechanism level. A retrieval system returned wrong-topic chunks with high confidence; the actual causes were three independent factors, none of them the first hypothesis. The second case applies the same decomposition discipline to an architectural decision made before the system existed.

May 2026 · Keystone blog

Provana AcuteCare: clinical copilot with guardrails

A clinical copilot with role-based action guardrails: three protocols, generative UI, four governance outcomes (Serve, Block, Route, Mutate). The prototype reused the same governance architecture from workplace safety to acute-care medicine without structural changes in this implementation, an engineering observation from one prototype, not evidence of general portability. Built at the Boston AI Tinkerers hackathon with Sai Gopal Jarabana.

May 2026 · Keystone blog

Governed incident response: agentic UI with RBAC and audit trails

An agentic incident-response prototype where role checks gate tool calls, actions are written to a hash-chained audit record, and the generated UI reflects the actions available to the user's role. Solo build for the AI Tinkerers Generative UI Hackathon.