Document HTML file behavior in the Agents Window

[ntrogh]

Product change

• Source: sessions: Open HTML files in integrated browser vscode#336287
• Merged: 2026-09-15T20:56:20Z

On desktop, opening an .html file in the Agents Window uses the integrated browser by default. HTML diff editors keep their existing editor association.

Why the docs need an update

docs/agents/run/agents-window.md only documents explicitly opening files in the integrated browser and does not explain the default HTML association or its diff-editor exception.

Suggested documentation

• docs/agents/run/agents-window.md: Add the default behavior for HTML files in the active session and clarify that diffs continue to open in a diff editor.

Acceptance criteria

• The desktop-only default for HTML files is documented.
• The distinction between ordinary HTML files and HTML diffs is clear.