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.

Written by the indexing model from the issue text.