On GitHub Copilot App 1.

On GitHub Copilot App 1.0.78-2 for Windows, extension canvas iframes do not receive/synchronize the documented canvas theme contract (`data-color-mode` and semantic theme CSS variables). The host is dark, but a project extension canvas renders light, including after extension reload and same-instance reopen.

---
| Field | Value |
| --- | --- |
| App version | 1.1.4 |
| OS | Windows 10.0.26220 |
| Theme | Rainglow Lavender |
| Path | /chat |
| Tenure | Week 15 |

The reported entry point is the extension canvas iframe in /chat; begin by reproducing the dark-host/light-canvas behavior on Windows, including extension reload and same-instance reopen. Trace where the documented data-color-mode contract and semantic theme CSS variables are passed into the iframe. Done means the canvas synchronizes with the host theme in each reported lifecycle case.

索引モデルが issue の本文から書いたものです。