feat: add copy button to code blocks in markdown preview

[Rushil Patel (rusp) (rushil-b-patel)]

Adds a GitHub-style copy button that appears on hover in the top-right corner of code blocks in the markdown preview. Clicking copies the code block content to the clipboard and shows a checkmark confirmation.

fixes: #322269

[Rushil Patel (rusp) (rushil-b-patel)]

@microsoft-github-policy-service agree

[Copilot]

Pull request overview

This PR adds a GitHub-style “copy code” affordance to the Markdown preview webview by injecting an icon-only button into rendered code blocks and styling it to appear on hover/focus, with a temporary “copied” checkmark state after activation.

Changes:

• Inject a copy button into each pre > code block on initial load and on preview content updates.
• Implement inline SVG icons (copy + check) and clipboard write behavior on click.
• Add CSS for positioning and hover/focus styling of the copy button within code blocks.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
extensions/markdown-language-features/preview-src/index.ts	Adds DOM injection and clipboard handling for code-block copy buttons in the preview webview.
extensions/markdown-language-features/media/markdown.css	Adds styling for the code-block copy button and updates <pre> positioning to support it.

[Rushil Patel (rusp) (rushil-b-patel)]

Hello Matt Bierner (@mjbvz), I see you have worked in markdown features.
Can you please check this PR ?
Thanks :)

[Rushil Patel (rusp) (rushil-b-patel)]

Hello Vritant Bhardwaj (@vritant24) Can you please delegate to appropriate person for this PR ?
Thanks

[Rushil Patel (rusp) (rushil-b-patel)]

Hello Henning Dieterichs (@hediet) any update here :) !

[Henning Dieterichs (hediet)]

Thanks for the PR!

[Rushil Patel (rusp) (rushil-b-patel)]

Hello Henning Dieterichs (@hediet) Thanks for your time.
Should I fix this failing test & push again ?
Edit: I think rebase should fix this !

[Rushil Patel (rusp) (rushil-b-patel)]

Hello Henning Dieterichs (@hediet), I rebase & pushed to avoid that failing check. Hope you won't mind.

Thanks : )

[Rushil Patel (rusp) (rushil-b-patel)]

Hello Henning Dieterichs (@hediet),

Sorry to bother you again for the approval, but the CI was failing because of outdated rebase so I had to rebase and push it again :)

[Rushil Patel (rusp) (rushil-b-patel)]

Hello Henning Dieterichs (@hediet) 👀 circling back on this : )

[Rushil Patel (rusp) (rushil-b-patel)]

Hello Benjamin Christopher Simmonds (@benibenj) : )
Checking up on this.