Add with_messages for scoping chat messages

lib/ruby_llm/active_record/acts_as_legacy.rb

@@ -151,6 +151,11 @@ def with_schema(...)
         self
       end
 
+      def with_messages(...)
+        to_llm.with_messages(...)
+        self
+      end
+
       def on_new_message(&block)
         to_llm
 

lib/ruby_llm/active_record/chat_methods.rb

@@ -139,6 +139,11 @@ def with_schema(...)
         self
       end
 
+      def with_messages(...)
+        to_llm.with_messages(...)
+        self
+      end
+
       def on_new_message(&block)
         to_llm
 

lib/ruby_llm/chat.rb

@@ -18,6 +18,7 @@ def initialize(model: nil, provider: nil, assume_model_exists: false, context: n
       with_model(model_id, provider: provider, assume_exists: assume_model_exists)
       @temperature = nil
       @messages = []
+      @messages_scope = nil
       @tools = {}
       @params = {}
       @headers = {}
@@ -97,6 +98,16 @@ def with_schema(schema)
       self
     end
 
+    def with_messages(&block)
+      if block.nil?
+        @messages_scope = nil
+        return self
+      end
+
+      @messages_scope = block
+      self
+    end
+
     def on_new_message(&block)
       @on[:new_message] = block
       self
@@ -123,7 +134,7 @@ def each(&)
 
     def complete(&) # rubocop:disable Metrics/PerceivedComplexity
       response = @provider.complete(
-        messages,
+        scoped_messages,
         tools: @tools,
         temperature: @temperature,
         model: @model,
@@ -169,6 +180,10 @@ def instance_variables
 
     private
 
+    def scoped_messages
+       @messages_scope.present? ? @messages_scope.call(messages) : messages
+    end
+
     def wrap_streaming_block(&block)
       return nil unless block_given?
 

spec/ruby_llm/chat_messages_scope_spec.rb

@@ -0,0 +1,88 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe RubyLLM::Chat do
+  include_context 'with configured RubyLLM'
+
+  describe '#with_messages' do
+    it 'uses all messages by default when no scope is configured' do
+      chat = RubyLLM.chat
+      provider = chat.instance_variable_get(:@provider)
+
+      allow(provider).to receive(:complete).and_return(
+        RubyLLM::Message.new(role: :assistant, content: 'Test response')
+      )
+
+      chat.add_message(role: :user, content: 'one')
+      chat.add_message(role: :assistant, content: 'two')
+
+      chat.complete
+
+      expect(provider).to have_received(:complete).with(
+        chat.messages,
+        hash_including(
+          tools: chat.tools,
+          temperature: anything,
+          model: chat.model,
+          params: chat.params,
+          headers: chat.headers,
+          schema: chat.schema
+        )
+      )
+    end
+
+    it 'applies a callable scope to the messages passed to the provider' do
+      chat = RubyLLM.chat
+      provider = chat.instance_variable_get(:@provider)
+
+      allow(provider).to receive(:complete).and_return(
+        RubyLLM::Message.new(role: :assistant, content: 'Scoped response')
+      )
+
+      first = chat.add_message(role: :user, content: 'first')
+      second = chat.add_message(role: :assistant, content: 'second')
+
+      chat.with_messages { |msgs| [msgs.last] }
+
+      chat.complete
+
+      expect(provider).to have_received(:complete) do |messages_arg, **_options|
+        expect(messages_arg).to eq([second])
+        expect(messages_arg).not_to include(first)
+      end
+    end
+
+    it 'can clear the scope by calling without a block' do
+      chat = RubyLLM.chat
+      provider = chat.instance_variable_get(:@provider)
+
+      allow(provider).to receive(:complete).and_return(
+        RubyLLM::Message.new(role: :assistant, content: 'Cleared scope response')
+      )
+
+      chat.add_message(role: :user, content: 'one')
+      chat.add_message(role: :assistant, content: 'two')
+
+      chat.with_messages { |msgs| [msgs.last] }
+      chat.with_messages
+
+      chat.complete
+
+      expect(provider).to have_received(:complete).with(
+        chat.messages,
+        hash_including(
+          tools: chat.tools,
+          temperature: anything,
+          model: chat.model,
+          params: chat.params,
+          headers: chat.headers,
+          schema: chat.schema
+        )
+      )
+    end
+
+  end
+end
+
+