Infinite rendering loop causing high CPU and memory growth

Summary

Claude Code entered an infinite rendering loop causing constant redraws, high CPU usage, and memory growth until requiring SIGKILL termination.

Symptoms

• Visual: Bottom ~10 lines of terminal constantly blinking/redrawing
• CPU: 96% sustained usage on single core
• Memory: Growing from 1.2GB → 2.0GB over 4 hours
• Unresponsive: Process ignored SIGTERM, required kill -9

System Information

• OS: Linux 6.8.0-84-generic
• Claude Code Model: claude-sonnet-4-5-20250929
• Process Runtime: 4+ hours before forced termination

Context When Bug Occurred

• Working with file editing operations
• Git operations (commits/pushes) completed successfully
• Bug triggered after tool output completion
• Multiple tools used in sequence (Read, Edit, Bash for git commands)

Process State

State: R (running)
CPU: 96% sustained
Memory: 1.2GB → 2.0GB (growing ~200MB/hour)
Threads: 15
Context Switches: Very high (1M+ voluntary)

Behavior

• Terminal showed constant redraws of same content
• No new output generated, just redrawing existing lines
• Process stuck in UI render loop (not I/O, not computation)
• Ignored SIGTERM, required SIGKILL

Expected Behavior

• Output should stabilize after tool completion
• Process should respond to SIGTERM
• Memory should remain stable when idle

Impact

• Instance became unusable
• High resource consumption
• Required force kill

Workaround

Force kill with kill -9 <PID> was necessary.

Additional Notes

A second Claude Code instance running concurrently on the same system functioned normally, suggesting the bug is triggered by specific conditions rather than being systemic.