diff --git a/src/app/api/machines/session/route.ts b/src/app/api/machines/session/route.ts
index 790f70f..a89775f 100644
--- a/src/app/api/machines/session/route.ts
+++ b/src/app/api/machines/session/route.ts
@@ -95,14 +95,22 @@ export async function GET(request: NextRequest) {
 
     if (!ensuredAssignedUserId && context.persona && context.assignedUserEmail) {
       try {
-        const ensuredUser = (await client.mutation(api.users.ensureUser, {
+        const ensureArgs: Record<string, unknown> = {
           tenantId: context.tenantId ?? DEFAULT_TENANT_ID,
           email: context.assignedUserEmail,
           name: context.assignedUserName ?? context.assignedUserEmail,
           avatarUrl: undefined,
           role: (context.assignedUserRole ?? context.persona ?? "collaborator").toUpperCase(),
-          companyId: context.companyId ?? undefined,
-        })) as { _id?: Id<"users">; name?: string | null; role?: string | null } | null
+        }
+        if (context.companyId) {
+          ensureArgs.companyId = context.companyId as Id<"companies">
+        }
+
+        const ensuredUser = (await client.mutation(api.users.ensureUser, ensureArgs)) as {
+          _id?: Id<"users">
+          name?: string | null
+          role?: string | null
+        } | null
 
         if (ensuredUser?._id) {
           ensuredAssignedUserId = ensuredUser._id as string