v2.1.27 hangs at 100% CPU after first response (v2.1.25 works)

Bug Report: v2.1.27 hangs at 100% CPU after first response

Environment

• Claude Code Version: 2.1.27
• Working Version: 2.1.25
• OS: macOS Darwin 25.2.0 (Apple Silicon)
• Model: Opus 4.5

Description

After starting a Claude Code session and receiving the first response, the CLI hangs at 100% CPU. The spinner shows but no further responses are possible. This happens consistently on v2.1.27 but NOT on v2.1.25.

Steps to Reproduce

1. Start Claude Code v2.1.27: claude
2. Enter any prompt (e.g., "hello")
3. Receive first response successfully
4. Enter second prompt
5. CLI hangs at 100% CPU, spinner shows "Billowing..." or similar but never completes

Troubleshooting Attempted

• [x] Disabled all plugins (27 plugins) - still hangs
• [x] Disabled all hooks (PreToolUse, PostToolUse, UserPromptSubmit, Stop) - still hangs
• [x] Disabled all MCP servers - still hangs
• [x] Disabled statusLine command - still hangs
• [x] Cleared debug files and file-history - still hangs
• [x] Vacuumed sessions.db - still hangs
• [x] Fresh session after /exit - still hangs

Workaround

Running v2.1.25 directly works without issues:

~/.local/share/claude/versions/2.1.25

Process State When Hung

claude  100.0%  CPU, ~500MB-2GB memory, R+ state (running)

Multiple Claude sessions can accumulate, all spinning at 100% CPU.

Binary Size Difference

• 2.1.25: 182,288,624 bytes
• 2.1.27: 179,283,440 bytes (3MB smaller)

Expected Behavior

CLI should remain responsive after first response and process subsequent prompts normally.

Actual Behavior

CLI spins at 100% CPU and becomes unresponsive after first successful response.