UI hangs on "Inferring..." when pasting a long prompt via copy-code button

Description

When a long block of text is copied using the in-app "copy code" button and then pasted into the Claude Code input field, the UI submits the message but then freezes permanently on "Inferring..." — the model never responds and the tab must be killed.

Typing the same content manually (or pasting shorter content) works correctly.

Steps to reproduce

1. Generate a long response in Claude Code that includes a code block (e.g. a context summary or long skill output).
2. Click the copy code button on that block to copy to clipboard.
3. Open a new Claude Code tab (or use an existing one).
4. Paste the copied text into the input field and press Enter / Send.
5. The message submits, the UI shows "Inferring...", and never advances.

Expected behavior

The message is processed normally and the model responds.

Actual behavior

UI is permanently stuck at "Inferring...". No error is shown. The tab must be closed.

Environment

• Platform: Windows 11 Pro (10.0.26200), Azure AD cloud PC
• Claude Code: VS Code native extension
• Observed: 2026-06-16

Additional context

The freeze appears specific to the copy-code button path — the same text pasted from another source (e.g. typed or copied from a text editor) does not reproduce the issue. Suspicion is that the clipboard content from the copy-code button has a hidden character, encoding difference, or length that triggers a hang in the submission pipeline before the request reaches the model.