LLM param in Assistant can be a registered LLM or custom adapter

That makes an Assistant open to very custom LLMs.

lib/langchain/assistant.rb

@@ -28,7 +28,7 @@ class Assistant
 
     # Create a new assistant
     #
-    # @param llm [Langchain::LLM::Base] LLM instance that the assistant will use
+    # @param llm [Langchain::LLM::Base, Langchain::Assistant::LLM::Adapters::Base] LLM instance that the assistant will use
     # @param tools [Array<Langchain::Tool::Base>] Tools that the assistant has access to
     # @param instructions [String] The system instructions
     # @param tool_choice [String] Specify how tools should be selected. Options: "auto", "any", "none", or <specific function name>
@@ -37,7 +37,6 @@ class Assistant
     # @param add_message_callback [Proc] A callback function (Proc or lambda) that is called when any message is added to the conversation
     def initialize(
       llm:,
-      llm_adapter: LLM::Adapter.build(llm),
       tools: [],
       instructions: nil,
       tool_choice: "auto",
@@ -51,7 +50,14 @@ def initialize(
       end
 
       @llm = llm
-      @llm_adapter = llm_adapter
+      case llm
+      when Langchain::LLM::Base
+        @llm_adapter = LLM::Adapter.build(llm)
+      when Langchain::Assistant::LLM::Adapters::Base
+        @llm_adapter = llm
+      else
+        raise ArgumentError, "LLM has to be object extending Langchain::LLM::Base or Langchain::Assistant::LLM::Adapters::Base"
+      end
 
       # TODO: Validate that it is, indeed, a Proc or lambda
       if !add_message_callback.nil? && !add_message_callback.respond_to?(:call)

spec/langchain/assistant/assistant_spec.rb

@@ -1561,22 +1561,43 @@ def initialize(role:, content: nil, image_url: nil, tool_calls: [], tool_call_id
 
     subject {
       described_class.new(
-        llm: llm,
-        llm_adapter: llm_adapter,
+        llm: llm_adapter,
         tools: [calculator],
         instructions: instructions
       )
     }
 
     describe ".new" do
-      it "initiates an assistant without error" do
-        expect { subject }.not_to raise_error
+      it "initiates an assistant without error using adapter as LLM" do
+        expect {
+          described_class.new(
+            llm: llm_adapter,
+            tools: [calculator],
+            instructions: instructions
+          )
+        }.not_to raise_error
+      end
+
+      it "raises an error when using unknown LLM" do
+        expect {
+          described_class.new(
+            llm: llm,
+            tools: [calculator],
+            instructions: instructions
+          )
+        }.to raise_error
       end
     end
 
     describe "#messages" do
       it "returns list of messages" do
-        expect(subject.messages).to contain_exactly(
+        expect(
+          described_class.new(
+            llm: llm_adapter,
+            tools: [calculator],
+            instructions: instructions
+          ).messages
+        ).to contain_exactly(
           an_object_having_attributes(
             role: "system",
             content: "You are an expert assistant"