TUI animation freezes during thinking→streaming state transitions on WSL2 + Windows Terminal

Describe the bug

The spinner and seconds counter animations freeze momentarily during state transitions — specifically when "thinking" begins and when the response starts streaming. The timer visibly stops updating for ~1-2 seconds at each transition point, then resumes. This happens on every interaction, not intermittently.

The freeze correlates with UI state changes (idle → thinking → streaming → idle), suggesting full-screen re-renders in Ink/Yoga are blocking the animation update loop during these transitions.

Related issues

This appears to share root cause with #769 and #1913 (screen flickering due to Ink re-renders), but manifests differently on WSL2 — as a freeze rather than a flicker, likely because the WSL2→Windows Terminal escape code pipe adds enough latency to make the re-render pause visible.

Also related: #21357 (yoga render loop causing 1M+ re-renders), #12234 (intermittent freezes on Windows Terminal), #34669 (TUI blocked after task completion on Windows Terminal).

Steps to reproduce

1. Run Claude Code on WSL2 with Windows Terminal
2. Send any prompt
3. Observe the spinner/seconds counter during the "thinking" phase
4. The animation freezes briefly when thinking starts, and again when the response begins streaming

Expected behavior

Spinner and timer should animate smoothly through state transitions without visible pauses.

Environment

| Component | Version |
|---|---|
| Claude Code | 2.1.79 |
| OS | Ubuntu 24.04.4 LTS (WSL2) |
| WSL | 2.6.2.0 |
| WSL Kernel | 6.6.87.2-microsoft-standard-WSL2 |
| WSLg | 1.0.71 |
| Windows | 10.0.26200.8037 |
| Windows Terminal | 1.23.20211.0 |
| Node.js | v22.22.1 |
| GPU | NVIDIA GeForce RTX 4070 Ti SUPER |
| CPU | 32-core x86_64 (Alder Lake) |
| RAM | 32 GB (25+ GB free during issue) |

Mitigations attempted (no effect on freeze)

• Enabled Atlas GPU rendering engine in Windows Terminal (useAtlasEngine: true, rendering.graphicsAPI: direct3d11)
• Set antialiasingMode: grayscale in Windows Terminal
• Reduced MCP server count from 27 to ~15 (removed failed/broken servers)
• Verified system is not under load (99% CPU idle, 25 GB free RAM)
• Created .wslconfig with autoMemoryReclaim=dropcache

Additional context

• The rendering stack is Ink (React for CLI) + Yoga (WASM layout engine), confirmed via binary analysis
• System resources are not a factor — the machine is effectively idle during the freeze
• The freeze is consistent and reproducible on every prompt, not intermittent
• The WSL2 pipe between the CLI process and Windows Terminal likely amplifies the re-render cost, turning what might be a sub-frame flicker on native terminals into a visible 1-2 second pause
• Higher effort/thinking levels make the freeze more noticeable, possibly because more UI state updates occur