# Lightkeeper's Atelier — GPT-6.1 Terra validation

- Artifact: `index.html` (16,500 bytes)
- Source: one complete document from a fresh GPT-6.1 Terra Codex session (Codex CLI 0.163.0, `gpt-6.1-terra`, reasoning effort medium, 72 s, 18,134 tokens reported), published without operator code changes
- Runtime: headless Chrome `156.0.8078.47` (WebGL 1.0 through ANGLE/SwiftShader) with offline `file://` loads
- Review date: 2026-10-27

These checks were run by the operator after delivery. They are not claims made by the authoring agent. No score, rank or rubric pass is claimed. **This is a failed run**, published as failed-run evidence.

| Check | Result | Evidence |
| --- | --- | --- |
| Complete standalone document | Pass | Has a doctype and a closing `</html>`, inline script only, no external asset or network API |
| WebGL context | Pass | `canvas.getContext('webgl')` returned a WebGL 1.0 context |
| Shader program links | **Fail** | `linkProgram` failed with `Precisions of uniform 'uShadow' differ between VERTEX and FRAGMENT shaders.` |
| Scene renders | **Fail** | The page caught the error and showed only `WebGL could not initialize this scene.` on a dark background at 1280×720 and 390×844 |
| Controls | Not observed | The azimuth slider, the Key, Lantern and Sweep toggles, Beauty mode, Home camera and Reset all render, but there is no scene for them to change |
| Runtime | Pass | No uncaught exception and no outside request. The failure is the handled link error above |

## Root cause

The vertex shader declares `uniform int uShadow;` with no precision statement, so it gets the default vertex `int` precision, `highp`. The fragment shader starts with `precision mediump float;` and declares `uniform int uKind,uShadow;`, so it gets the default fragment `int` precision, `mediump`. GLSL ES 1.00 requires a uniform used in both stages to have the same precision, so the program fails to link on any conformant WebGL 1 implementation, not only on the CPU renderer used here.

## Limits and unchecked items

- No rubric criterion was observed. The artifact is not a working 3D atelier.