In a saucepan, combine the cranberries, water, and sugar and bring to a gentle boil, then cook for 8–10 minutes, stirring occasionally, until the cranberries burst completely and the liquid turns deep red and aromatic.
Remove from heat, add the rosemary sprigs, and let steep off heat for 10 minutes only so the herbal aroma stays subtle and clean, then strain through a fine-mesh sieve, pressing gently on the solids, stir in the pinch of fine sea salt, and let the syrup cool completely.
In a pitcher, combine 120 ml of the cooled cranberry rosemary syrup with the fresh orange juice and stir to integrate, tasting to confirm the base is sharp, lightly bitter, and balanced rather than sweet.
Fill the pitcher generously with ice, pour in the chilled club soda, and stir very gently once or twice to combine without flattening the carbonation.
Pour into ice-filled glasses, garnish with fresh cranberries and rosemary sprigs, and serve immediately while cold and lively.
