Short answer: Jainism is a distinct and eternal dharma of its own, not a branch of Sanatan Dharma. In Jainism, the path (dharma) is taught by the Tirthankaras and guided by its own scriptures (like the Agamas) and principles such as ahimsa, anekantavada, and aparigraha. Sanatan Dharma is a term often used for what many people call Hinduism, describing an eternal, universal order or duties. While the two share a common Indian spiritual milieu and some overlapping values, Jainism maintains its separate identity and lineage. Digambar and Śvetāmbar traditions both regard Jainism as independent, with its own siddhantas and canonical texts. You can read more here