Startup Performance Profiling

What: Optional profiling system to measure Claude Code's startup performance and memory usage across initialization phases.

How to use:

# Enable startup profiling
CLAUDE_CODE_PROFILE_STARTUP=1 claude

# The profiling report will automatically display after startup showing:
# - Time elapsed at each checkpoint (absolute and delta)
# - Memory usage (RSS and heap) at each checkpoint
# - Total startup time

Details:

• Tracks 30+ checkpoints throughout the startup sequence
• Records both timing (via Node.js perf_hooks) and memory metrics
• Zero overhead when disabled (default)
• Useful for diagnosing slow startup issues or investigating performance regressions
• Evidence: o5() at line 3881, RB9() at line 3891, B80() at line 3919, profiler initialization in aqA at line 3926