Summary

This PR refactors the PowerMetricsManager to use an in-memory circular buffer instead of writing to temporary files, eliminating the unbounded file growth issue where /tmp/all-smi_powermetrics_* files would grow at ~7MB/hour for long-running instances.

Problem

• Powermetrics was writing to temp files that grew continuously (1.2GB/week)
• No rotation or truncation mechanism existed
• Files required sudo privileges to clean up
• Disk space could be exhausted on systems with limited /tmp capacity

Solution

Implemented a pipe-based approach with in-memory circular buffer:

• Capture powermetrics stdout directly via pipe
• Store last 120 samples (2 minutes) in a VecDeque circular buffer
• Dedicated reader thread processes stdout lines without blocking
• Remove all file-based operations and cleanup logic

Benefits

• Zero disk usage - no temporary files created
• Better performance - eliminates file I/O overhead
• More secure - no sensitive metrics data written to disk
• Simpler cleanup - no sudo rm operations needed

Implementation Details

• BufReader prevents stdout buffer deadlock
• lines() iterator ensures only complete lines are processed
• Process restart functionality maintained with new channel creation
• Tests updated to work with buffer-based approach

Test plan

• Unit tests pass
• Build completes without warnings
• Manual testing shows powermetrics data collection works
• Long-running test to verify no disk usage growth
• Verify process restart handling works correctly