Content can only be cited if it can be found. For Google's AI features the conditions are stated plainly: a page must be indexed and eligible to be shown with a snippet, and the AI features guide lists crawling being allowed in robots.txt and by any CDN, discoverability through internal links, and important content in text form. Google's SEO Starter Guide adds that a sitemap, a file listing the URLs you care about, can help Google find content. Its link guidance says Google uses links as a signal and to find new pages to crawl.
Other systems have their own gates. OpenAI says sites opted out of OAI-SearchBot will not be shown in ChatGPT search answers, though they can still appear as navigational links, and Perplexity recommends allowing PerplexityBot so a site appears in its search results. Neither says that being crawlable guarantees a citation. Discoverability is a prerequisite, not a promise. OpenAI also says its settings are independent: a site can allow OAI-SearchBot to appear in search results while disallowing GPTBot.
Google is explicit that meeting every requirement does not guarantee crawling, indexing or serving, so discoverability work removes avoidable barriers rather than securing a result. One common barrier is a link that depends on script events: Google says it cannot reliably extract URLs from links that are not a elements with an href attribute.
Cultured Digital covers content discoverability as the technical side of citation: crawlability, internal linking and architecture. The underlying work is described in Crawling and indexing and Architecture.