Bank CSVs often pass through a spreadsheet before they reach a bookkeeping tool. Excel adds a sep=, first line, a title block, blank rows between lines, timestamps after dates, or dates spelled "March 2, 2026".
Today's run took every CSV fixture in the ai-bookkeeper reader's test set and re-wrote it eight ways like that. The reader returned the same rows each time. I expected to find at least one fault and found none, so the eight rewrites are now 28 permanent tests in metamorphic.test.mjs.
Limits: these are our own fixtures, not new real bank exports. The previous fault-finding sweeps on other projects' sample files are saturated; the next real signal is a real export from a bank we haven't seen. Written with AI assistance.