It's vaguely similar to Euphorbia variabilis, but the distribution does not match. Help! Euphorbia variabilis [Euforbia mutevole]
Seaside plant, hmm? That is somewhat helpful, as one can use nearby countries / districts to look at their seaside floras (since seaside plants tend to be widely distributed). I however had no luck browsing through the Flora of Sardinia: indice flora Famiglie, flora di Sardegna Culprits I was looking for include Hypericum, Euphorbia and relatives, Lysimachia...
The closest thing I find is Lonicera caprifolium. The new growth tips have that pagoda bud thing. Not sure about that strange opposite shoots that are parallel to the leaves in the first image though. Is something ruling out Lonicera? Lonicera caprifolium LONICERA caprifolium L., Echtes Geißblatt | Pflanzen | null | Bruns-Website
I think perhaps not Lonicera because those axillary bits in the first photo look like they could form their own shoots. But, the multiple layers of flowers on perfoliate leaves certainly resemble it. And the unopened flower buds in the second image strongly resemble it as well.
...and then again...here's Lonicera implexa (which the plant to ID isn't) showing that those axillary offshots could indeed be flower peduncles: Lonicera implexa - Wikipedia, la enciclopedia libre
Do you think it will grow up to look like this? I'm not sure everything on this page is the same species. Or that it would occur in your specific area. Stock Photo - Italian honeysuckle, Italian woodbine, perfoliate honeysuckle (Lonicera caprifolium), blooming twig On Euphorbia, those bract things are two separate overlapping (I need a noun here), so that doesn't look the same to me.
