[autoantohaki]

Before: relay-logs printed a file once and exited, so watching a live log meant falling back to tail -f.

After: relay-logs -f app.log prints the last 10 lines and then every line appended to the file, colored by level. -n sets how many lines to start with, and several files can be followed at once with their lines interleaved as they arrive.

The follower only prints complete lines, so a line that is still being written is never split. It starts over when a file is truncated, reads the new file from its first line after log rotation, and waits for a file that does not exist yet.

How: followFile polls the file's size and identity (device, inode, birth time) and reads only the new byte range through the existing LineSplitter. readLastLines reads backwards in 64 KB blocks to find the starting point. mergeSources races the sources' iterators so one quiet or failing file does not hold up the others. Tests cover tail, partial lines, truncation, rotation, late files, and merging.