Lister relocates urban memory from proprietary social platforms into the institutional question of civic technological sovereignty. The paper proposes a citizen-generated urban memory archive hosted through the decentralised architecture of the Fediverse, with Mastodon serving as an indicative technical model. Its iconic idea is that collective digital memory should function as a civic public good: publicly owned, interoperable, citizen-curated and capable of surviving the closure or strategic decisions of private platforms. Methodologically, the paper combines literature on social memory, digital archives, learning cities and civic technology with a speculative infrastructural design. Questions of moderation, consent, anonymity and privacy are treated as constitutive archival decisions rather than peripheral governance problems. The wider contribution is to link memory studies to platform studies and public infrastructure. Urban remembrance becomes inseparable from protocols of ownership and persistence. The archive is therefore not simply a store of representations of the city; it is a civic institution whose technical architecture determines who may contribute, who governs continuity and under what conditions shared memory remains accessible.