fix: complete display and channel group management

src/server/routes/playback.ts

@@ -91,11 +91,20 @@ export function registerPlaybackRoutes(
         const groupId = requireUuidParam(context, "groupId");
         const store = createSignageStore(context.services.database);
         const groups = await store.listChannelGroups();
+        const group = groups.find((candidate) => candidate.group.id === groupId);
+        if (!group) {
+          throw new SignageError("SIGNAGE_NOT_FOUND");
+        }
         if (groups.length <= 1) {
           // An installation always has somewhere for a viewer to land.
           throw new SignageError("SIGNAGE_CONFLICT", { reason: "last-group" });
         }
-        await store.deleteChannelGroup(groupId);
+        const fallbackGroup = groups.find((candidate) => candidate.group.id !== groupId);
+        const fallbackChannel = fallbackGroup?.channels.find((channel) => channel.isDefault);
+        if (!fallbackChannel) {
+          throw new SignageError("SIGNAGE_CONFLICT", { reason: "no-fallback-channel" });
+        }
+        await store.deleteChannelGroup(groupId, fallbackChannel.id);
         return new Response(null, { status: 204 });
       });
     },