Generative artificial intelligence (GenAI) is rapidly integrating into educational practices, yet its impact on teacher professional practice within the highly context and relationship-dependent field of early childhood education remains poorly understood. This study explores how GenAI functions as a "digital scaffold" to support novice preschool teachers in de-signing contextualized, kindergarten-based curriculum within the Chinese context. Through in-depth interviews and thematic analysis with 10 teachers, we discovered GenAI's dual potential: it empowers educators by providing instant re-sources and inspiration, yet its "decontextualized" outputs create tension with the contextual and relational core of early childhood education. Crucially, teachers demonstrated robust professional agency by critically evaluating and localizing AI-generated content. This process of "mediated reflection" catalyzed their professional knowledge development. Ultimately, AI integration does not replace teachers but re-configures their professional roles toward higher-value, human-centered core competencies-situational judgment, ethical decision-making, and emotional connection-which form the bedrock of resilient and sustainable educational ecosystems. Our findings underscore that responsible AI integration in education must prioritize sup-porting teacher agency and well-being to enhance systemic sustainability.