Sandpaper turns the rich HTML documents Claude Code or Codex makes for you into a living surface you refine by talking to the page — instead of reading the doc here and re-describing changes over there in a terminal, you change it in place, and it stays the canonical spec your build is based on.
The problem: the medium for thinking with an agent got richer (markdown → HTML with diagrams,
tables, mockups), but the loop didn't — you still steer it from another window.
The bet: read the rich document and change it in place, with the explicitly selected
Claude Code or Codex provider rewriting the file as the single source of truth and showing live status.
Status: Green · Rung 1 — the spine · internal provider registry · zero runtime deps · saved provider auth
The problem, the bet, who it's for, where it stops.
The experience, the modes, and provider status on the page.
The invariant, the data flow, the modules, one turn end-to-end.
structured provider adapters, file-as-truth, the dumb pipe — narrated.