diff --git a/src/ipc.ts b/src/ipc.ts
index 043b07a..a454fdf 100644
--- a/src/ipc.ts
+++ b/src/ipc.ts
@@ -441,7 +441,10 @@ export async function processTaskIpc(
           );
           break;
         }
-        // Defense in depth: agent cannot set isMain via IPC
+        // Defense in depth: agent cannot set isMain via IPC.                                                                                                                                    
+        // Preserve isMain from the existing registration so IPC config                                                                                                                          
+        // updates (e.g. adding additionalMounts) don't strip the flag.                                                                                                                          
+        const existingGroup = registeredGroups[data.jid];
         deps.registerGroup(data.jid, {
           name: data.name,
           folder: data.folder,
@@ -449,6 +452,7 @@ export async function processTaskIpc(
           added_at: new Date().toISOString(),
           containerConfig: data.containerConfig,
           requiresTrigger: data.requiresTrigger,
+          isMain: existingGroup?.isMain,
         });
       } else {
         logger.warn(