Activity
Every change is a file.
The pipeline writes what it did as it does it: a capture, a filing, a publication. This log is the same record the rail counts, read in full.
Record
One record per motion.
Each motion is written once, with its kind, the subject it touched and the moment it happened. Nothing is rewritten in place, so the log is a history rather than a state.
Subject
A subject you can follow.
A motion names the record it touched, so a post can show the trail that produced it and the log can say which changes a reader is able to see.
Replay
The same log, two ways.
The page is a build-time read of the log; the tool that writes it can also follow it live, so the archive's history and its live view cannot disagree.