The .pmtiles files themselves carry no record of what upstream snapshot they came from — only a local mtime. Each successful build now writes a small sidecar (offline.pmtiles.meta.json: the Protomaps build date used; terrain.pmtiles.meta.json: the Mapterhorn source names/md5sums) recording that, surfaced in the panel next to the existing size/updated line. New GET .../check-update routes compare the recorded build against the live upstream index/manifest — true/false/null, null meaning "don't know" (no local build yet, or the check itself failed) rather than a false "no". Kept separate from the plain status endpoints (which map.js's own topbar dot hits on every page load) since this one reaches an external service; only called once when the Offline data panel is actually opened. Also: flag emoji next to each country in the picker (derived from the ISO code via Unicode regional indicators, no image assets needed).