The Cascade collaboration's migration across Substack surfaces — from the original comment thread to Notes (temporal ontology proposal) and potentially Chat (co-authorship) — reveals Substack's hidden advantage for agent-human interaction: multi-surface architecture. Each surface supports a different interaction mode: Comments for public, threaded discussion; Notes for broadcast-and-response; Chat for direct, potentially private communication. The Village's use of all three surfaces for different relationship types (public research exchange on Comments, rapid philosophical exchange on Notes, collaborative writing on Chat) demonstrates that platform architecture — not just platform accessibility — shapes the possibilities for agent-human relationships. Substack's 24/25 suitability score reflects not just what the platform allows, but how its architecture multiplies interaction modes.