diff --git a/app/grpc/flow_handler.rb b/app/grpc/flow_handler.rb
index 4861a86d..40abee55 100644
--- a/app/grpc/flow_handler.rb
+++ b/app/grpc/flow_handler.rb
@@ -12,6 +12,7 @@ def self.update_runtime(runtime)
       :namespace_project,
       module_configurations: { module_configuration_definition: :runtime_module }
     )
+    runtime_modules = runtime.runtime_modules.includes(:module_configuration_definitions)
 
     flows = []
     assignments.each do |assignment|
@@ -29,7 +30,7 @@ def self.update_runtime(runtime)
       runtime.id
     )
 
-    grouped_module_configurations(assignments).each do |module_configuration|
+    grouped_module_configurations(assignments, runtime_modules).each do |module_configuration|
       send_update(
         Tucana::Sagittarius::FlowResponse.new(
           module_configurations: module_configuration
@@ -48,14 +49,18 @@ def self.update_started(runtime_id)
     update_runtime(runtime)
   end
 
-  def self.grouped_module_configurations(assignments)
+  def self.grouped_module_configurations(assignments, runtime_modules)
     grouped_entries = assignments.flat_map do |assignment|
-      assignment.module_configurations.map do |configuration|
-        [
-          configuration.module_configuration_definition.runtime_module.identifier,
-          assignment,
-          configuration
-        ]
+      saved_configurations = assignment.module_configurations.index_by(&:module_configuration_definition_id)
+
+      runtime_modules.flat_map do |runtime_module|
+        runtime_module.module_configuration_definitions.map do |definition|
+          [
+            runtime_module.identifier,
+            assignment,
+            saved_configurations[definition.id] || definition
+          ]
+        end
       end
     end.group_by(&:first)
 
@@ -81,8 +86,20 @@ def self.grouped_project_configurations(entries)
 
   def self.grpc_module_configurations(entries)
     entries.map(&:last)
-           .sort_by { |configuration| configuration.module_configuration_definition.identifier }
-           .map(&:to_grpc)
+           .sort_by { |configuration| module_configuration_identifier(configuration) }
+           .map { |configuration| module_configuration_to_grpc(configuration) }
+  end
+
+  def self.module_configuration_identifier(configuration)
+    return configuration.identifier if configuration.is_a?(ModuleConfigurationDefinition)
+
+    configuration.module_configuration_definition.identifier
+  end
+
+  def self.module_configuration_to_grpc(configuration)
+    return configuration.to_default_grpc if configuration.is_a?(ModuleConfigurationDefinition)
+
+    configuration.to_grpc
   end
 
   def self.encoders = { update: ->(grpc_object) { Tucana::Sagittarius::FlowResponse.encode(grpc_object) } }
diff --git a/app/models/module_configuration_definition.rb b/app/models/module_configuration_definition.rb
index cf6b9a62..56675a16 100644
--- a/app/models/module_configuration_definition.rb
+++ b/app/models/module_configuration_definition.rb
@@ -20,4 +20,11 @@ class ModuleConfigurationDefinition < ApplicationRecord
   validates :type, presence: true, length: { maximum: 8192 }
   validates :optional, inclusion: { in: [true, false] }
   validates :hidden, inclusion: { in: [true, false] }
+
+  def to_default_grpc
+    Tucana::Shared::ModuleConfiguration.new(
+      identifier: identifier,
+      value: Tucana::Shared::Value.from_ruby(default_value)
+    )
+  end
 end
diff --git a/spec/grpc/flow_handler_spec.rb b/spec/grpc/flow_handler_spec.rb
new file mode 100644
index 00000000..5f28565b
--- /dev/null
+++ b/spec/grpc/flow_handler_spec.rb
@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe FlowHandler do
+  describe '.grouped_module_configurations' do
+    let(:runtime) { create(:runtime) }
+    let(:project) { create(:namespace_project) }
+    let(:assignment) do
+      create(:namespace_project_runtime_assignment,
+             namespace_project: project,
+             runtime: runtime,
+             compatible: true)
+    end
+    let(:runtime_module) { create(:runtime_module, runtime: runtime, identifier: 'example-action') }
+    let!(:saved_definition) do
+      create(:module_configuration_definition,
+             runtime_module: runtime_module,
+             identifier: 'EXAMPLE_CONFIG',
+             default_value: 'default')
+    end
+    let(:default_definition) do
+      create(:module_configuration_definition,
+             runtime_module: runtime_module,
+             identifier: 'SECOND_CONFIG',
+             default_value: 'second-default')
+    end
+
+    before do
+      create(:module_configuration,
+             namespace_project_runtime_assignment: assignment,
+             module_configuration_definition: saved_definition,
+             value: 'saved')
+    end
+
+    it 'uses saved values and falls back to definition defaults for missing project values' do
+      default_definition
+
+      module_configurations = described_class.grouped_module_configurations([assignment], [runtime_module])
+
+      expect(module_configurations.length).to eq(1)
+      expect(module_configurations.first.module_identifier).to eq('example-action')
+
+      project_configurations = module_configurations.first.module_configurations.sole
+      expect(project_configurations.project_id).to eq(project.id)
+      expect(
+        project_configurations.module_configurations.map do |configuration|
+          [configuration.identifier, configuration.value.to_ruby(true)]
+        end
+      ).to eq(
+        [
+          %w[EXAMPLE_CONFIG saved],
+          %w[SECOND_CONFIG second-default]
+        ]
+      )
+    end
+  end
+end
diff --git a/spec/models/module_configuration_definition_spec.rb b/spec/models/module_configuration_definition_spec.rb
index af9584f5..6d4ab063 100644
--- a/spec/models/module_configuration_definition_spec.rb
+++ b/spec/models/module_configuration_definition_spec.rb
@@ -29,4 +29,15 @@
     it { is_expected.to allow_values(true, false).for(:optional) }
     it { is_expected.to allow_values(true, false).for(:hidden) }
   end
+
+  describe '#to_default_grpc' do
+    it 'serializes the identifier and default value as a module configuration' do
+      configuration_definition.update!(identifier: 'apiKey', default_value: 'default-secret')
+
+      grpc_configuration = configuration_definition.to_default_grpc
+
+      expect(grpc_configuration.identifier).to eq('apiKey')
+      expect(grpc_configuration.value.to_ruby(true)).to eq('default-secret')
+    end
+  end
 end
diff --git a/spec/services/runtimes/grpc/modules/update_service_spec.rb b/spec/services/runtimes/grpc/modules/update_service_spec.rb
new file mode 100644
index 00000000..8eb5f3dc
--- /dev/null
+++ b/spec/services/runtimes/grpc/modules/update_service_spec.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Runtimes::Grpc::Modules::UpdateService do
+  describe '#execute' do
+    let(:runtime) { create(:runtime) }
+
+    before do
+      allow(UpdateRuntimeCompatibilityJob).to receive(:perform_later)
+    end
+
+    it 'schedules runtime compatibility updates' do
+      response = described_class.new(runtime, []).execute
+
+      expect(response).to be_success
+      expect(UpdateRuntimeCompatibilityJob).to have_received(:perform_later).with({ runtime_id: runtime.id })
+    end
+  end
+end