Interleaving logs from ikiwiki and the kernel:

[Wed May 02 15:50:32.307921 2018] [cgi:error] [pid 4914:tid 3031423808] [client] AH01215: To /home/b-waldeneffect-org/source.git: /var/www/b-waldeneffect-org/ikiwiki.cgi, referer:
[Wed May 02 15:50:32.308000 2018] [cgi:error] [pid 4914:tid 3031423808] [client] AH01215:    0c67dc578..893cc6e9b  master -> master: /var/www/b-waldeneffect-org/ikiwiki.cgi, referer:
May 02 15:50:50 pell kernel: ikiwiki[5054]: segfault at bf7d3ffc ip b6ec9e63 sp bf7d4000 error 6 in[b6ec7000+11000]
[Wed May 02 15:50:50.222077 2018] [cgi:error] [pid 4914:tid 3031423808] [client] End of script output before headers: ikiwiki.cgi, referer:
[Wed May 02 16:15:48.013597 2018] [cgi:error] [pid 10708:tid 2838391616] [client] AH01215:    893cc6e9b..c4f23b861  master -> master: /var/www/b-waldeneffect-org/ikiwiki.cgi, referer:
[Wed May 02 16:15:57.921670 2018] [cgi:error] [pid 10708:tid 2838391616] [client] AH01215: /home/b-waldeneffect-org/public_html/pending/Pros_and_cons_of_the_community_garden/index.html independently created, not overwriting with version from pending/Pros_and_cons_of_the_community_garden: /var/www/b-waldeneffect-org/ikiwiki.cgi, referer:

So, apparently an img directive led to libmarkdown segfaulting, crashing ikiwiki after it had rendered a html file but before it made note that it had done so.

The user saw an "Internal server error" and hit reload, which failed due to the "independently created, not overwriting" check. The site was then wedged not accepting edits until manually fixed.

After deleting the html file, ikiwiki --refresh successfully built things, without libmarkdown segfaulting this time. I don't know if this was a transient libmarkdown bug or a memory glitch.

Either way, seems that ikiwiki could better handle recovery from this kind of scenario. The "independently created" check has a security benefit... Perhaps ikiwiki could keep a log file of destdir files it's recently created but has yet to record in the index, and then the check can be skipped for those files.