As more users ask AI systems for information, AI-search platforms are becoming a common gateway to web information. Unlike traditional search, which maps keywords to ranked pages, AI search retrieves pages, filters sources, selects citations, and generates answers before users see sources. This selection layer may amplify source bias and turn source choice into a security question. If a platform repeatedly cites domains where new users can publish posts easily, ordinary publication on those domains can become an indirect path into AI-search citations and answer text. Measuring this path is hard: platforms reveal little about citation selection, citations change over time, and the web contains so much background content that later answer changes are hard to attribute to our posts. We present a measurement framework for identifying and measuring this low-barrier publication path, combining cross-platform citation mapping, publication-barrier testing, and marker-controlled publication experiments. Across 10 AI-search platforms, we analyze 17,211 citation instances over 6,356 unique source domains and find: (1) citations concentrate in platform-specific sources, with top-20 domains capturing 20.5--70.8% of per-platform citations, and 15 of 22 tested publication platforms tied to cited source domains had low or medium barriers for both account setup and posting; (2) in our experiments, ordinary publication on preferred platforms changed what entered AI-search outputs: 8 of 10 platforms cited a fabricated concept within seven days, and one high-preference-platform article had greater citation impact than over 20 matched low-preference posts; and (3) this path is commercially available: a $14 GEO purchase produced 13 public posts, and one AI-search platform cited GEO-posted content with our designed markers within one hour.

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