Beacon
A 65 KB agentic RAG workspace — grounded, verifiable citations and human-approved actions, with zero runtime UI libraries. Built for air-gapped enterprise where every npm dependency is a liability.
“In an air-gapped enterprise, every dependency you ship is a dependency someone has to audit.”
The Problem
Agentic copilots in regulated environments live or die on two things: can you trust what the model says, and can you trust what it does. A hallucinated citation is a compliance incident. An unapproved action is a breach. And the typical answer — pulling in a streaming library, a markdown renderer, a UI framework — is exactly the wrong move when the deployment target is air-gapped and every transitive package is a supply-chain question someone has to answer.
The Approach
Beacon is a homage to Cohere's North — an agentic RAG workspace with grounded citations, human-in-the-loop action approval, and span-level feedback. The front end ships zero runtime UI, markdown, or streaming libraries. The SSE reader is hand-built over fetch, the citation renderer is bespoke, and there's a mini-markdown parser written from scratch. Cohere v2 (Command for generation, Embed for retrieval, Rerank for relevance) drives the backend over FastAPI, streaming ten typed event kinds to a React 19 client.
Key Insight
The interesting engineering isn't the model — it's treating the model's output as untrusted input. Citation spans arrive as raw character offsets; Beacon clamps them to valid ranges, snaps them to word boundaries, and drops overlaps before a single character is highlighted. Streamed tokens are batched with requestAnimationFrame so React commits once per frame instead of once per token. Hand-building these primitives wasn't nostalgia — it's what makes a 65 KB gzipped bundle, and an auditable one, possible.
How it works
The architecture behind the system.
Grounded, Verifiable Citations
Every claim traces back to a source span. The custom citation renderer ties generated text to retrieved evidence so answers are checkable, not just plausible.
Human-Approved Actions
The agent proposes; the human disposes. Actions surface for explicit approval before execution — the human-in-the-loop gate that regulated workflows require.
Hand-Built SSE Reader
Ten typed event kinds streamed over a fetch-based Server-Sent Events reader written from scratch — no streaming library, no hidden dependencies in the hot path.
Untrusted Citation Spans
Model-emitted span offsets are treated as hostile input: clamped to valid ranges, snapped to word boundaries, and de-overlapped before anything is rendered.
One Commit Per Frame
Streamed tokens are batched with requestAnimationFrame so React commits once per frame instead of once per token — smooth streaming without thrashing the DOM.
Mini-Markdown From Scratch
A bespoke mini-markdown parser and renderer replace a full markdown library, keeping the bundle tiny and every byte of parsing logic auditable.