[BUG] VSCode Extension: Task tool output opens as plaintext instead of rendered markdown

Environment

• Platform: VSCode Extension
• Claude Code version: 2.0.5
• Operating System: macOS 15.6.1
• IDE: VSCode

Bug Description

When a subagent (Task tool) produces output containing markdown, the collapsed preview in the Claude Code chat window correctly renders the markdown with formatting. However, when clicking to expand the output, VSCode opens it in a new tab as plaintext, losing all markdown formatting. There is no option to view the expanded output with markdown rendering.

Steps to Reproduce

1. Use the Task tool to spawn a subagent that produces markdown output
2. Observe the collapsed output in the chat window - markdown is rendered nicely
3. Click to expand the output
4. A new VSCode tab opens (titled something like "Task tool output (rando-#s&letters)")
5. The tab displays the content as plaintext instead of rendered markdown

Expected Behavior

One of the following:

• The expanded view should render markdown like the collapsed preview does
• There should be an "expand in place" option that shows the full rendered markdown within the chat window
• The VSCode tab should open as a markdown preview rather than plaintext

Actual Behavior

• Collapsed preview: Markdown is properly rendered ✓
• Expanded in new tab: Only plaintext display, no markdown rendering ✗
• No way to see the expanded, formatted version

Additional Context

This issue likely generalizes to all markdown or otherwise previewable output from tools, not just Task tool output. The UX is inconsistent - users see nice formatting in the preview but lose it when they want to read the full content.