Fix double-escaped entities in renderAsPlaintext code spans

[roblourens]

For #303752

I think this is ok but please take a quick look @mjbvz

Problem

Text inside markdown code spans (e.g. foo & bar) rendered through renderAsPlaintext came out double-escaped — & appeared as &, </> as </>. This surfaced in the agent sessions list, where a local (VS Code harness) session's in-progress description is derived from a tool invocation message via getInProgressSessionDescription → renderAsPlaintext.

Root cause

In createPlainTextRenderer, the codespan handler called escape(text). But marked already HTML-escapes code span text during tokenization. The trailing unescape pass in renderAsPlaintext only reverses a single level, so the extra escape() left entities double-escaped. Code blocks were unaffected because marked passes their text raw (escaped exactly once).

Input	Before	After
Run \tests & build``	Run tests & build	Run tests & build
Use \``	Use &lt;form&gt;	Use <form>

Fix

Remove the redundant escape() from the codespan plaintext renderer so it matches code-block behavior. Added a regression test.

This is a shared low-level helper, so the fix corrects the same double-escaping for all renderAsPlaintext callers (hovers, pickers, etc.), not just the agent sessions list.

(Written by Copilot)

[Copilot]

Pull request overview

Fixes renderAsPlaintext producing double-escaped HTML entities inside Markdown inline code spans (`...`) by removing an extra escaping step in the plaintext renderer, aligning code span handling with marked’s own token escaping.

Changes:

• Stop re-escaping marked codespan token text in createPlainTextRenderer to prevent double-escaped entities.
• Add a regression test ensuring entities/HTML-like content in code spans renders as expected in plaintext output.

Show a summary per file

File	Description
src/vs/base/browser/markdownRenderer.ts	Removes redundant escaping in the plaintext codespan renderer to avoid double-escaped entities.
src/vs/base/test/browser/markdownRenderer.test.ts	Adds a regression test covering plaintext rendering of code spans containing escapable characters/entities.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 1