Spent some time discovering and unfortunately it's Windows's bug in loopback interface.
I wrote a test demo (blocking mode) to exchange data and watched their packets, found that network stack would drop packets when congestion control algorithm is set to BBR2. It seems the second data exchange was broken.

In T5993#201111, @werner wrote:

For example Poppler uses GnuPG comment packets to lower its own attack surface by leaving all OpenPGP handling to gpg. The patch (or at least the version we noticed in Fedora and Debian) entirely breaks this use.

(The commits had a wrong bug it in their message)

It might be useful to have samples of compressed keys:

No, we can't do much about this. It has always been easy to create compression bombs and the more relevant thing here is compressed signed or encrypted data. Or just compressed mails. The patch by @DemiMarie is way to complicated for what it wants to achieve and actually breaks existing use cases. For example Poppler uses GnuPG comment packets to lower its own attack surface by leaving all OpenPGP handling to gpg. The patch (or at least the version we noticed in Fedora and Debian) entirely breaks this use.

Using the primary key for ssh was not intended and thus not tested. I have not yet found the time too look closer at your report. Just one remark:

In T7620#200845, @Saturneric wrote:

I think it would be much better if GnuPG automatically performed a key listing immediately after key generation when a smartcard is involved. This would allow GnuPG to detect the presence of the subkey on the card right away, rather than leaving it marked as a stub until the user manually lists keys.

I see that you generated the secret encryption subkey with backup. This means that the secret subkey is generated on your computer, then copied to the card, and then deleted from your computer. The deletion is the reason why the subkey is marked as stub. Only after listing the keys on the card gpg notices that the secret key is actually on the card.

btw, my clue was that in that last --check-sigs, if i used --debug-all i got this:

This affects certification-only primary keys when doing web-of-trust calculations.

Hi Werner, I submitted a patch right after this bug report using AC_CHECK_DECLS([_sys_siglist]) [1].

To avoid further noise on this ticket, i've done as requested and posted to gnupg-devel : (https://lists.gnupg.org/pipermail/gnupg-devel/2025-May/035875.html

The first call of get_key receives the following key listing from gpg:

2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: sec:-:256:19:C4A24EB0B5F2E025:1746474606:::u:::s
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: cESCA:::D2760001240100000006180489130000::brainp
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: oolP256r1:23::0:<LF>
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: fpr:::::::::DEC0948C398A6E7B50746EC6C4A24EB0B5F2
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: E025:<LF>
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: grp:::::::::06BDACFBDEDBC5783A75AE5E7251FA3369C4
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: 0FF4:<LF>
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: uid:-::::1746474606::2222D8E2F373B9BDEE0DEA2A20A
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: 9402214E9F984::Eric <eric@bktus.com>::::::::::0:
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: <LF>
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: ssb:-:256:19:EAFC5EA29B758B22:1746474606::::::a:
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: ::D2760001240100000006180489130000::brainpoolP25
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: 6r1:23:<LF>
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: fpr:::::::::1AD596DDEC9B8CF3C1AC6C41EAFC5EA29B75
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: 8B22:<LF>
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: grp:::::::::52F0797C0B0439BBD718E2534D46656A6C45
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: 6A78:<LF>
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: ssb:-:256:18:A874804DB497B91C:1746474606::::::e:
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: ::#::brainpoolP256r1:23:<LF>
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: fpr:::::::::33B273C7BD46E4EB63DD6874A874804DB497
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: B91C:<LF>
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: grp:::::::::34A1F8D9B2AA0CF07C2E042D70E10F9D4EBE
2025-05-05 21:50:23 gpgme[57059]     _gpgme_io_read: check: E734:<LF>

Note the line

ssb:-:256:18:A874804DB497B91C:1746474606::::::e:::#::brainpoolP256r1:23:<LF>

where the # marks the subkey as stub.

Right now we have

Interesting, that sounds like a portable method. I am not very familiar with GPG internals, but to me that sounds like quite a bit of work. Unless there is another benefit to doing so, I don't think it is worth it just to print signal names.

I have now identified the exact conditions and a reproducible path for the issue I previously reported. I will also attach the relevant gpgme.log.

I doubt that this is a gpgme problem. With a gpgme log we will be able see the exact commands send to gpg and replicate this on the command line.

And the US administration might even change the definition of a year to, say, 100 months so that potus can rightfully keep his promise that there won't be more election in the foreseeable future ;-)

By the way, "years" is also "incorrect" once in ~4 years because it uses n*365 days. Werner's advice still applies. Enter an ISO date if you want an exact date. Or use a UI tool like Kleopatra.

The main problem here was that this all is not async-safe and thus I once implemented only the standard cases I could test easily.

The logs of gpgme would be helpful, i.e. run your test program with GPGME_DEBUG=8:$(pwd)/gpgme-$(date +"%Y-%m-%d-%H%M%S").log to create a log file with gpgme's logs.

For the records:

A bug tracker shall never be used for discussion because the audience is not as expected. Only very few people follow a certain bug but several hundreds are following discussion on gnupg-devel@. That is basic hacker knowledge.

I am surprised that you don't want to use the issue tracker for issues.
GnuPG's trust calculations are quite clearly broken, by any metric. There's nothing to discuss here.

Heiko, I told you already in T7106 that it is not a good idea to re-open a ticket. If you really want to discuss stuff, take that to a mailing list.

I see two interesting angles from which to think about this Web of Trust calculation:

Yes, this is related to T7547. With my last fix for that I overlooked that we use PUBKEY_USAGE_CERT to internally request the primary key but that one is not set because in general USAGE_SIG means the same (except for some case in PGP7 mode).

> I'm not sure i understand why "the latest" should be preferred.

A bit more experimentation shows the same behavior, even if Alice's tsig of Bill is full, not marginal, and even if all signatures are made in the same second, which is the finest resolution that OpenPGP objects can report.