It would appear that there are two classes of 502s served by textboard.org. When deps/server.scm responds with
(define (500-handler req params err)
`(500 () ,(string-append
"Something went wrong: "
;; TODO: should probably not leak this in production:
(condition/report-string err))))nginx rewrites this to a 502 but nothing bad like aborting the running instance actually happens. This is why the frontpageless posting >>16 test could be followed up by the explanatory post without any trouble. This class of 502 errors is inelegant but mostly harmless.
The stress tests from the previous thread and the string-split attack >>20 do abort the running instance, and nginx makes a 502 from scratch. These are not quite as harmless, which is why explanations and solutions were posted but not the detailed wget reproduction.
Since the first class of 502s is mostly harmless, there are plenty of them that can be found in MIT/GNU Scheme's HTTP libraries.