fix(communication): adopt legacy general chat rooms safely

backend/src/routes/communication.ts

@@ -88,13 +88,13 @@ export default async function communicationRoutes(server: FastifyInstance) {
             .onConflictDoNothing()
     }
 
-    const ensureGeneralRoom = async (tenantId: number, creatorId: string) => {
-        let [room] = await server.db.select().from(communicationRooms)
-            .where(and(eq(communicationRooms.tenantId, tenantId), eq(communicationRooms.key, "allgemein")))
-            .limit(1)
+    const ensureGeneralRoom = async (tenantId: number, creatorId: string) => server.db.transaction(async (tx) => {
+        const generalKey = and(eq(communicationRooms.tenantId, tenantId), eq(communicationRooms.key, "allgemein"))
+        let [room] = await tx.select().from(communicationRooms)
+            .where(generalKey).limit(1).for("update")
 
         if (!room) {
-            const [created] = await server.db.insert(communicationRooms).values({
+            const [created] = await tx.insert(communicationRooms).values({
                 tenantId,
                 key: "allgemein",
                 name: "Allgemeiner Chat",
@@ -104,16 +104,28 @@ export default async function communicationRoutes(server: FastifyInstance) {
             }).onConflictDoNothing().returning()
             room = created
             if (!room) {
-                [room] = await server.db.select().from(communicationRooms)
-                    .where(and(eq(communicationRooms.tenantId, tenantId), eq(communicationRooms.key, "allgemein")))
-                    .limit(1)
+                [room] = await tx.select().from(communicationRooms)
+                    .where(generalKey).limit(1).for("update")
             }
         }
 
-        if (room.type !== "general" || room.archived) chatError("Allgemeiner Chat ist nicht verfügbar", 409)
-        await addMembers(room.id, (await tenantUsers(tenantId)).map((user) => user.userId))
+        // Old Matrix general-room endpoints omitted the type and persisted its default 'room'.
+        // Only unarchived, unbound tenant rooms may be adopted; a key collision must not grant access.
+        if (!room || !["general", "room"].includes(room.type) || room.archived
+            || room.entityType !== null || room.entityId !== null || room.entityUuid !== null) {
+            chatError("Allgemeiner Chat ist nicht verfügbar", 409)
+        }
+        if (room.type === "room") {
+            [room] = await tx.update(communicationRooms).set({ type: "general" })
+                .where(eq(communicationRooms.id, room.id)).returning()
+        }
+        const users = await tx.select({ userId: authTenantUsers.user_id }).from(authTenantUsers)
+            .where(eq(authTenantUsers.tenant_id, tenantId))
+        if (users.length) await tx.insert(communicationRoomMembers)
+            .values([...new Set(users.map(user => user.userId))].map(userId => ({ roomId: room.id, userId })))
+            .onConflictDoNothing()
         return room
-    }
+    })
 
     const requireRoom = async (req: any, tenantId: number, userId: string, roomKey: string) => {
         const [row] = await server.db.select({ room: communicationRooms }).from(communicationRooms)