An empty live feed is not live data

A server whose marker source is unconfigured answers 200 with an empty array,
and the client counted that as success. The deployed map came up with no pins
at all, wearing a green "live data" badge — which is the one outcome worse than
having no badge, because the badge exists precisely so a fabricated demo cannot
be mistaken for real data, and here it was doing the reverse.

Empty now falls back to the sample set and keeps saying "sample".

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/adapters/http.ts

@@ -167,6 +167,12 @@ export function createTeraClient(options: TeraApiOptions = {}): TeraClient {
     async markers(): Promise<MarkerFeed> {
       const body = await get<MarkersBody>("/markers");
       if (!body || !Array.isArray(body.markers)) return sampleMarkerFeed();
+      // An API that answers with nothing is the default posture of a server
+      // whose marker source has not been configured, and it is indistinguishable
+      // to a viewer from a broken map. Fall back, and — more importantly — go on
+      // saying "sample", because the alternative is an empty map wearing a
+      // "live data" badge, which is the one outcome worse than no badge at all.
+      if (body.markers.length === 0) return sampleMarkerFeed();
       return {
         // A `WireMarker` *is* a `Marker` with a provenance field on it, so this
         // is a widening and not a translation — which is the property