Last month I wrote about auditing 34 days of multi-model Claude Code usage and finding that a single missing model line was half my overspend. The core of that piece was a boring engineering decision: ingest every assistant message from Claude Code's session files into an append-only log keyed by message.id, and never let the source rewrite history.
This is the follow-up I didn't plan to write. The same log just caught two accounting bugs in splitrail, a 216-star Rust usage tracker for agentic CLIs — and within twelve days of the first report, both were fixed in an official release: one through my PR, one through a maintainer-authored patch that adopted the report's analysis. Here's the play-by-play, with the numbers.
Bug 1: your history quietly rewrites itself
Claude Code rewrites session JSONL files in place when you resume or compact a conversation. Between two scans of the same file, five of my assistant messages vanished — usage that was already incurred, gone from the record. Any tracker that recomputes totals from live files inherits this drift: yesterday's numbers change while you sleep.
I filed it as #200. The maintainer confirmed the mechanism the same day — splitrail re-read live files, so messages removed by resume/compaction disappeared from historical totals — and shipped a fix in 3.6.0: a local SQLite history store that persists normalized usage and merges it with current session data before deduplication. Fast, clean work.
