VSCode sticky user message header hides assistant responses in long turns

Description

When a user message is tall (e.g. pasting compiler output, logs, or large code blocks), the assistant's response within the same turn becomes completely invisible, hidden behind the sticky user message header.

Root cause

User messages in the chat have position: sticky; z-index: 2; top: 0 (the .stickyHeader CSS class). This is designed to keep the user's prompt visible while scrolling through the AI's response. However, when the user message is taller than the viewport, the sticky element's visual extent covers the entire assistant response area below it. Since the sticky header has z-index: 2 and the timeline/assistant messages have z-index: auto, the assistant responses render behind the sticky user message and are completely invisible.

Example

• User pastes 2510px of compiler output
• Assistant responds with thinking + text + tool calls (~476px total)
• The sticky user message pins to top: 0 and extends to y≈367 in the viewport
• All assistant messages (y=142 to y=371) are painted behind the sticky header
• The user sees compiler output, then the next user message, with no visible AI response in between

CSS rules involved

.message_07S1Yg.stickyHeader_07S1Yg {
  position: sticky;
  z-index: 2;
  top: 0;
  background-image: linear-gradient(...);
}
.message_07S1Yg.stickyHeader_07S1Yg:has([aria-expanded=true]) {
  z-index: 3;
}

Reproduction

1. Open a session in VSCode/Cursor
2. Paste a large block of text (e.g. 50+ lines of compiler output or logs) as a user message
3. Wait for the AI to respond with tool calls
4. Scroll through the turn. The assistant's response (text, tool calls, thinking) is invisible

Verified fix

Remove sticky positioning entirely; the conversation should be a linear scroll:

.message.stickyHeader {
  position: relative;  /* was: sticky */
  z-index: auto;       /* was: 2 */
  /* remove top: 0 and background-image gradient */
}

Tested by patching webview/index.css; assistant responses become visible, no visual regressions observed.

Version

Claude Code 2.1.109