Steps to replicate the issue (include links if applicable):

• visit https://en.wikipedia.org/wiki/Wikipedia_talk:WikiProject_Articles_for_creation
• in the archive box search at the top right, type "Backlog drives", then click search

What happens?:

• the URL https://en.wikipedia.org/wiki/Special:Search?fulltext=Search+noticeboards+%26+archives&fulltext=Search&prefix=Wikipedia+talk%3AWikiProject+Articles+for+creation%2F&search=backlog+drive&ns0=1 is outputted, which has 2 fulltext parameters

What should have happened instead?:

• the URL should have 1 or 0 fulltext parameters
• its value should be truthy/falsy, instead of a random-ish string. https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/core/+/HEAD/includes/specials/SpecialSearch.php

Software version (skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):

• what does the fulltext parameter do? is it documented somewhere? do we need to add it to https://www.mediawiki.org/wiki/Help:CirrusSearch or similar?
• that &ns1=1 looks unnecessary since specifying a prefix causes it to be ignored. maybe we should make a ticket to chop that off if a prefix is specified. if the code that controls this is back end rather than front end