Differential report: od, nl, comm, fmt, join, numfmt against GNU coreutils 9.12

[karolkulesza]

Hi, I ran uutils 0.12.0 and main (2fb77e8) against GNU coreutils 9.12 (built from source) on six utilities that have no fuzz target yet: od, nl, comm, fmt, join, numfmt. 1000 generated cases per utility, sandboxed, Linux aarch64. The full report (per-feature parity, clustered divergences with minimized repros, and the corpus to re-run it) is here:

https://github.com/port-anything/showcases/tree/main/coreutils

Per-feature parity on main: od 90.5%, nl 81.3%, comm 99.6%, fmt 92.6%, join 98.6%, numfmt 99.9%. Most of what's left is --help/error-message wording.

Everything new is already filed, one issue each:

• numfmt: rejects scientific notation in fields that are not selected #15312, od: traditional option -B is not accepted #15313, od: -S/--strings ignores "cannot skip past end of combined input" #15314: fixed already, thanks!
• Two small number-parsing differences: od -w accepts a size suffix, nl -l rejects huge values #15551 od -w1K accepted / nl -l with a huge value rejected
• numfmt: a tab between fields is kept, GNU prints a space #15552 numfmt keeps a tab between fields
• fmt -p: an unprefixed last line without a newline gets one added #15553 fmt -p adds a newline to an unprefixed last line

The rest is already tracked (#10725, #13608, PR #12459, #5162, and several rows of the flagdiff list in #15254), so I didn't file it again; the README lists which divergence maps to which issue. Happy to re-run on a newer main or on other utilities if that's useful.

[jayhemnani9910]

One fmt divergence that isn't in the list: with -t, a paragraph that is a single wrapped line gets its continuation lines indented by the first line's indent plus 4. GNU uses 3 spaces when the first line starts at column 0 and no indent after the prefix otherwise (printf 'ab cd ef gh ij kl mn\n' | fmt -t -w10). Fixed in #15712; the rest of fmt's wrapping difference stays with #5162.