fix: add race condition guard and null check in group queries

- createOrFindPackageGroup: catch unique constraint violation from
  concurrent creates and fall back to findFirst
- createManualGroup: guard against empty package results before
  accessing first element

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/telegram/queries.ts

@@ -609,6 +609,9 @@ export async function createManualGroup(name: string, packageIds: string[]) {
     where: { id: { in: packageIds } },
     select: { sourceChannelId: true },
   });
+  if (pkgs.length === 0) {
+    throw new Error("No matching packages found");
+  }
   const channelIds = new Set(pkgs.map((p) => p.sourceChannelId));
   if (channelIds.size > 1) {
     throw new Error("Cannot group packages from different channels");

worker/src/db/queries.ts

@@ -553,16 +553,27 @@ export async function createOrFindPackageGroup(input: {
 
   if (existing) return existing.id;
 
-  const group = await db.packageGroup.create({
-    data: {
-      mediaAlbumId: input.mediaAlbumId,
-      sourceChannelId: input.sourceChannelId,
-      name: input.name,
-      previewData: input.previewData ? new Uint8Array(input.previewData) : undefined,
-    },
-  });
-
-  return group.id;
+  try {
+    const group = await db.packageGroup.create({
+      data: {
+        mediaAlbumId: input.mediaAlbumId,
+        sourceChannelId: input.sourceChannelId,
+        name: input.name,
+        previewData: input.previewData ? new Uint8Array(input.previewData) : undefined,
+      },
+    });
+    return group.id;
+  } catch (err) {
+    // Handle race condition: another process created the group between our findFirst and create
+    if (err instanceof Error && err.message.includes("Unique constraint")) {
+      const raced = await db.packageGroup.findFirst({
+        where: { mediaAlbumId: input.mediaAlbumId, sourceChannelId: input.sourceChannelId },
+        select: { id: true },
+      });
+      if (raced) return raced.id;
+    }
+    throw err;
+  }
 }
 
 export async function linkPackagesToGroup(