[BUG] Claude Code v2.1.27 freezes with 100% CPU on Synology NAS (Linux 4.4 kernel) — v2.1.25 works fine

Bug Description

Claude Code v2.1.27 freezes with 100% CPU usage on Synology NAS immediately after the user sends any message. The REPL mounts successfully and the prompt appears, but upon submitting any input (even a simple "hi"), the process enters a CPU-bound infinite loop and becomes completely unresponsive.

v2.1.23 and v2.1.25 work perfectly on the same system. Only v2.1.27 exhibits this behavior.

Environment

• Platform: Synology NAS, DSM 7.3.2
• Kernel: Linux 4.4.302+ (SMP, x86_64)
• CPU: Intel Celeron J4125 @ 2.00GHz (4 cores)
• RAM: 17GB
• glibc: 2.36
• Claude Code: v2.1.27 (also tested v2.1.23 and v2.1.25)
• Installation: Native installer (curl -fsSL https://claude.ai/install.sh | sh)

Steps to Reproduce

1. Install Claude Code v2.1.27 on a Synology NAS (DSM 7.x, Linux 4.4 kernel)
2. Run claude from terminal (SSH)
3. Wait for the REPL prompt to appear (startup completes successfully)
4. Type any message (e.g., "hi") and press Enter
5. The process immediately jumps to ~95-100% CPU and becomes unresponsive
6. No output is produced; the terminal is frozen
7. kill -9 is required to terminate the process

Non-interactive mode also freezes:

claude -p "say hello"   # Hangs at 100% CPU, never returns

Expected Behavior

Claude Code should process the message and return a response, as it does with v2.1.23 and v2.1.25.

Actual Behavior

Process enters a CPU-bound loop (State: R, ~100% CPU) and never produces output. Debug log shows startup completes normally but no entries appear after the user submits a message.

Process state during freeze (/proc/<pid>/status):

State:    R (running)
VmSize:   74692796 kB
VmRSS:    445100 kB
Threads:  8
voluntary_ctxt_switches:    985
nonvoluntary_ctxt_switches: 5612

The high ratio of nonvoluntary to voluntary context switches confirms the process is CPU-bound (spinning), not waiting on I/O.

Version Comparison

| Version | Result |
|---------|--------|
| v2.1.23 | Works — responds instantly |
| v2.1.25 | Works — responds instantly |
| v2.1.27 | Freezes — 100% CPU, no response |

Tested with identical settings, same system, same terminal session:

~/.local/share/claude/versions/2.1.23 -p "say hello"  # ✅ Returns immediately
~/.local/share/claude/versions/2.1.25 -p "say hello"  # ✅ Returns immediately
~/.local/share/claude/versions/2.1.27 -p "say hello"  # ❌ 100% CPU, never returns

Debug Log (v2.1.27)

Startup completes without errors:

[STARTUP] setup() completed in 35ms
[STARTUP] Commands and agents loaded in 9ms
[STARTUP] showSetupScreens() completed in 441ms
[STARTUP] MCP configs loaded in 478ms
Ripgrep first use test: PASSED (mode=system, path=rg)
[REPL:mount] REPL mounted, disabled=false
AutoUpdaterWrapper: Installation type: native
Checking for native installer update to version 2.1.27
Found 2.1.27 at .../claude, skipping install

No further log entries appear after user input — the freeze occurs silently.

Additional Notes

• Workaround: Downgrade to v2.1.25 by relinking ~/.local/bin/claude → ~/.local/share/claude/versions/2.1.25
• Auto-update disabled via DISABLE_AUTOUPDATER=1 env to prevent regression
• A secondary issue was also found: the built-in ripgrep binary fails on this kernel (Ripgrep first use test: FAILED), resolved by setting USE_BUILTIN_RIPGREP=0. However, this is separate from the v2.1.27 freeze — the freeze occurs even after ripgrep is working correctly.
• The same NAS hardware runs Claude Code successfully inside a Docker container (code-server), suggesting the issue is specific to the native binary on the Linux 4.4 kernel.

Possibly Related Issues

• #19393 — High CPU usage (100%+) when idle (v2.1.12)
• #18532 — Complete Freeze 100% CPU (v2.1.9, macOS ARM64)
• #13161 — ripgrep failure on FreeBSD (non-standard kernel)