Infinite rendering loop causing high CPU and memory growth #9684

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.