[BUG] VS Code extension: assistant text and tool outputs disappear during streaming

Bug Description

When using Claude Code in the VS Code extension (webview panel), two types of content intermittently disappear:

1. Assistant text messages — text rendered during streaming/processing appears briefly, then vanishes when the next UI update occurs (e.g., a tool call starts). The text is gone permanently and does not reappear.

1. Tool calls — when multiple tool calls are executed (e.g., 3 parallel Bash commands), some are missing entirely from the rendered conversation — both the call itself (input) and its output. For example, 3 commands run but only 1 is visible in the UI.

This happens across conversations — not tied to a specific session. No consistent trigger pattern identified.

Steps to Reproduce

1. Open Claude Code in VS Code (extension webview, not terminal)
2. Ask Claude to perform a multi-step task involving text responses and multiple tool calls
3. Observe that some assistant text disappears after briefly rendering
4. Observe that some tool calls (input + output) are missing from the conversation

Expected Behavior

All assistant text and all tool calls should persist in the conversation view.

Actual Behavior

• Assistant text appears during streaming, then vanishes on the next render update
• Some tool calls from parallel executions are not displayed at all (neither input nor output)

Environment

| Component | Version |
|-----------|---------|
| Claude Code | 2.1.38 |
| VS Code | 1.109.0 (x64) |
| OS | WSL2 (Linux 5.15.167.4-microsoft-standard-WSL2) on Windows |
| Platform | linux x64 |

Additional Context

• Happens in the VS Code webview panel, not the CLI terminal
• Not session-specific — reproduces across new conversations
• No specific trigger pattern — affects both pure text responses and tool call blocks
• Happens regardless of whether thinking is collapsed or expanded