[BUG] Interleaved thinking causes text to render character-by-character in TUI and IDE plugin

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Description

When interleaved-thinking-2025-05-14 beta header is active, the TUI and IDE plugin render
text responses character-by-character, with each character appearing as a separate list item
interleaved with "Thought for 0s" blocks.

Environment

• Claude Code version: 2.1.117
• OS: macOS (arm64)
• Occurs in: CLI TUI + CatPaw IDE plugin

Steps to Reproduce

1. Start a new Claude Code session
2. Ask any question that triggers interleaved thinking
3. Observe the response rendering

Expected Behavior

Text renders normally as continuous output.

Actual Behavior

Each character appears as a separate bullet point, interleaved with "Thought for 0s" blocks:

• 我
• Thought for 0s
• 发
• Thought for 0s
• 现
• ...

Root Cause (identified)

The request header includes interleaved-thinking-2025-05-14 (hardcoded in CLI source).
This causes the API to return interleaved thinking and text content blocks in the stream.
The TUI renderer does not correctly handle interleaved block types — it renders each delta
event as a new list item instead of grouping by block index.

Setting alwaysThinkingEnabled: false or effortLevel: low in ~/.claude/settings.json
does NOT fix the issue because the beta header is hardcoded.

Workaround

None currently available from user side.

What Should Happen?

The correct rendering logic should be:

On content_block_start → create a new block slot by index, type is either thinking or text
On content_block_delta → append the delta to the existing block at that index
On content_block_stop → finalize and render that block
thinking blocks render as a collapsible "Thought for Xs" summary, text blocks render as normal continuous text.

What's happening now is the renderer skips the grouping step — every content_block_delta event triggers a new render item regardless of index or type, so each character becomes its own bullet point with a "Thought for 0s" in between.

Error Messages/Logs

Steps to Reproduce

1

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.117 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_