tests/fuzzDoc.ts generates documents from a seeded PRNG (marks, lists,
tables, indents, XML-hostile text); fuzz-roundtrip.test.ts runs 50 seeds
through buildOdt -> importOdt and diffs the normalized JSON, naming the
failing seed. normalize/firstDiff moved out of roundtrip.test.ts into
tests/normalize.ts for reuse. The generator documents what is lossy by
design: default-equal marks in headings, indents and start in nested lists.