Chat view does not show active file indicator when opening a file in Markdown Editor Mode

**VS Code Version:**
Version: 1.133.0-insider (user setup)
Commit: 2a084000e4f05e682580153cd96a94847fec52ae
Date: 2026-08-11T10:13:30Z
Electron: 42.8.0
ElectronBuildId: 14845705
Chromium: 148.0.7778.280
Node.js: 24.18.0
V8: 14.8.178.38-electron.0
@github/copilot: 1.0.79-6
@github/copilot-sdk: 1.0.9
OS: Windows (or your OS here)

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**Steps to Reproduce:**

1. Open a Markdown file while the editor is in **Markdown Editor Mode**

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**Expected Result:**
The opened file should be automatically recognized as the **active file** in the Chat view, with the active file indicator displayed as usual.

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**Actual Result:**
No active file indicator appears in the Chat view.

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**Additional Observation:**
When I switch the editor mode from **Markdown Editor** to **Text Editor**, the active file indicator immediately appears in the Chat view. After switching back to **Markdown Editor**, the indicator continues to work correctly and does not disappear again.