Make sign up Magic Links work across devices

Previously if someone started signing in on their phone, but finished it on their laptop, they'd end up on the menu screen with no account. Bu tracking the purpose of a Magic Link we can always direct the user to sign up if they requested a magic link through sign up. This also makes the logic for changing the copy in the email more robust.

test/controllers/sessions/magic_links_controller_test.rb

@@ -9,17 +9,32 @@ class Sessions::MagicLinksControllerTest < ActionDispatch::IntegrationTest
     end
   end
 
-  test "create" do
+  test "create with sign in code" do
     identity = identities(:kevin)
     magic_link = MagicLink.create!(identity: identity)
 
     untenanted do
       post session_magic_link_url, params: { code: magic_link.code }
-    end
 
-    assert_response :redirect
-    assert cookies[:session_token].present?
-    assert_not MagicLink.exists?(magic_link.id), "The magic link should be consumed"
+      assert_response :redirect
+      assert cookies[:session_token].present?
+      assert_redirected_to landing_path, "Should redirect to after authentication path"
+      assert_not MagicLink.exists?(magic_link.id), "The magic link should be consumed"
+    end
+  end
+
+  test "create with sign up code" do
+    identity = identities(:kevin)
+    magic_link = MagicLink.create!(identity: identity, purpose: :sign_up)
+
+    untenanted do
+      post session_magic_link_url, params: { code: magic_link.code }
+
+      assert_response :redirect
+      assert cookies[:session_token].present?
+      assert_redirected_to new_signup_completion_path, "Should redirect to signup completion"
+      assert_not MagicLink.exists?(magic_link.id), "The magic link should be consumed"
+    end
   end
 
   test "create with invalid code" do