harness

Notion embedded coding agents into its workspace in a few weeks using the Cursor SDK, so an @mention now plans, builds, tests and opens a PR without an editor in sight. The SDK turns the harness that powers Cursor into a callable runtime, and that is a bigger shift than any model release.

Six weeks after agent harness engineering got named, the empirical question arrived: how much of a coding agent's score is the model, and how much is the scaffold around it. Four 2026 papers put numbers on it — and the numbers are larger than almost anyone guessed.

Vercel open-sourced eve at Ship London — a framework where an agent is a folder of files. We built 75 agents on it and ran an adversarial review. Here's what holds up, what breaks, and the stateful-on-stateless tension the launch posts skip.

On June 7, 2026, X renamed the agent loop 'loop engineering' and called it the successor to harness engineering. We ran 47 Claude Code loops in a sandbox to test the claims. The naming churns; three of the technical findings are real and one is measurable to the cent.

Two near-simultaneous coiners (Mitchell Hashimoto and Viv Trivedy), seven convergent voices, and twelve coding agents that all built the same primitives independently. A discipline crystallized in nine months — what it is, who built it, and what every shipping product now contains.

Fred Schott shipped Flue — a TypeScript framework that treats the agent harness as a first-class build target. Updated for the 1.0 Beta rewrite through beta.4, the new Actions primitive, @flue/react, the Cloudflare runtime deal, the Vercel-backed eve rival, and a fellow framework author's critique of what Flue makes first-class.