[BUG] Windows Terminal input completely frozen starting from v2.1.30 (regression from v2.1.29)

Bug Description

Claude Code becomes completely unresponsive to keyboard input on Windows Terminal starting from v2.1.30. The screen appears frozen — no characters can be typed, and the input prompt is non-functional. Downgrading to v2.1.29 immediately resolves the issue.

Environment

• OS: Windows 11
• Terminal: Windows Terminal (native, not WSL)
• Shell: PowerShell / Git Bash (both affected)
• Node.js: v20.11.0
• Installation: npm (@anthropic-ai/claude-code)

Reproduction Steps

1. Install Claude Code v2.1.30: npm install -g @anthropic-ai/claude-code@2.1.30
2. Open Windows Terminal
3. Run claude
4. Attempt to type anything into the prompt
5. Result: No input is accepted. Screen appears completely frozen.

Expected Behavior

The prompt should accept keyboard input normally (as it does in v2.1.29).

Root Cause Analysis

Binary diff analysis of the bundled cli.js between v2.1.29 and v2.1.30 reveals the following significant changes:

1. New useInterval hooks (0 → 5)

v2.1.29 had zero useInterval-based animation hooks. v2.1.30 introduces 5 new useInterval hooks running at 50ms–1000ms intervals:

| Hook | Interval | Purpose |
|------|----------|---------|
| Spinner position animation | 50ms / 200ms | Glimmer effect calculation |
| Stalled detection timer | 100ms | Tracks request duration |
| Stalled intensity interpolation | 50ms | Smooth animation easing |
| Team name animation | 1000ms | UI counter increment |
| Elapsed time tracker | 100ms | Duration display |

Each interval triggers a React state update → full Ink re-render → ANSI escape sequence generation → stdout write.

2. Rewritten spinner component

The spinner component was completely rewritten with new Box layout (flexWrap:"wrap", height:1, width:2), a reducedMotion parameter, and a reversed animation frame array — all adding layout computation overhead per render cycle.

3. Additional reactive state

| Metric | v2.1.29 | v2.1.30 | Diff |
|--------|---------|---------|------|
| useInterval hooks | 0 | 5 | +5 |
| useRef | 144 | 153 | +9 |
| useState | 542 | 545 | +3 |
| setTimeout | 302 | 308 | +6 |
| useMemo | 83 | 87 | +4 |
| spinner/animation refs | 182 | 204 | +22 |

Why this breaks on Windows Terminal

Ink (React for CLI) re-renders the entire screen buffer on every state change. On macOS/Linux terminals with Synchronized Output (DEC mode 2026), these rapid re-renders are batched and handled efficiently. However, Windows Terminal's ConPTY layer processes ANSI sequences significantly slower, causing:

1. Rapid useInterval callbacks (50–100ms) trigger continuous React re-renders
2. Each re-render writes ANSI sequences to stdout via ConPTY
3. ConPTY cannot drain the output buffer fast enough
4. stdout write() blocks the Node.js event loop
5. Blocked event loop cannot process stdin (keyboard input)
6. Result: Screen appears frozen, input is impossible

prefersReducedMotion does NOT fix this

v2.1.30 added a prefersReducedMotion config option. Testing confirmed it does not resolve the issue — it only changes the visual representation (blinking dot instead of animated spinner) but the underlying useInterval hooks continue firing at the same frequency.

Suggested Fix

• Gate useInterval hooks behind a ConPTY/Windows detection check, or significantly increase their intervals on Windows (e.g., 500ms+ instead of 50ms)
• Make prefersReducedMotion: true actually disable or throttle the interval hooks, not just change visuals
• Consider using requestAnimationFrame or passive rendering instead of aggressive interval-based re-renders

Workaround

Downgrade to v2.1.29:

npm install -g @anthropic-ai/claude-code@2.1.29

Related Issues

• #18084 — Severe screen flickering in VS Code/Cursor integrated terminal on Windows (same Ink re-rendering root cause)
• #10736 — Windows Terminal Input Stream Loss After Command Execution
• #19637 — Windows cmd rendering issue since v2.1.3