The hash becomes the single serialized view (snippet / Datasets list / a dataset
/ new-dataset form / Chart Builder). url-hash is the sole reader/writer of
location+history (total, never-throwing parse; hash-only canonical URLs).
UrlStateSync grows from the modal↔URL seam into the full router: state→hash is
derived from the stores (so in-modal dataset sub-views reach the hash), hash→state
restores on load and on Back/Forward, validating ids and cleaning stale links.
startRouting() runs after store hydrate.
