feat: start on AI integration

lib/bds/ai/chat_message.ex

@@ -0,0 +1,41 @@
+defmodule BDS.AI.ChatMessage do
+  @moduledoc false
+
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  @foreign_key_type :string
+  @roles [:system, :user, :assistant, :tool]
+
+  schema "chat_messages" do
+    belongs_to :conversation, BDS.AI.ChatConversation, references: :id, type: :string
+
+    field :role, Ecto.Enum, values: @roles
+    field :content, :string
+    field :tool_call_id, :string
+    field :tool_calls, :string
+    field :token_usage_input, :integer
+    field :token_usage_output, :integer
+    field :cache_read_tokens, :integer
+    field :cache_write_tokens, :integer
+    field :created_at, :integer
+  end
+
+  def changeset(message, attrs) do
+    message
+    |> cast(attrs, [
+      :conversation_id,
+      :role,
+      :content,
+      :tool_call_id,
+      :tool_calls,
+      :token_usage_input,
+      :token_usage_output,
+      :cache_read_tokens,
+      :cache_write_tokens,
+      :created_at
+    ], empty_values: [nil])
+    |> validate_required([:conversation_id, :role, :created_at])
+    |> assoc_constraint(:conversation)
+  end
+end