This paper proposes a novel retrieval framework, SPARC (Soft Probabilistic Adaptive Retrieval Model via Codebooks), to address the core challenges of multi-interest modeling in real-world recommender systems (RS). To overcome the fixed interests and passive matching strategies of existing methods, we utilize the Residual Quantized Variational Autoencoder (RQ-VAE) to construct a discrete interest space that dynamically evolves based on user behavior, and introduce a probabilistic interest module that predicts the probability distribution of the entire interest space. This shifts the paradigm from "passive matching" to "active exploration" in online inference, effectively enhancing the discovery of new interests. A/B testing on an industry platform with tens of millions of daily active users showed results such as +0.9% increase in user watch time, +0.4% increase in page views, and +22.7% increase in PV500 (new content reaching 500 PV within 24 hours). In offline evaluation using the Amazon Product dataset, we also confirmed improvements in Recall@K and NDCG@K metrics.