Add support for the developer role in chat completion messages

internal/apischema/openai/openai.go

@@ -12,6 +12,7 @@ import (
 // Chat message role defined by the OpenAI API.
 const (
 	ChatMessageRoleSystem    = "system"
+	ChatMessageRoleDeveloper = "developer"
 	ChatMessageRoleUser      = "user"
 	ChatMessageRoleAssistant = "assistant"
 	ChatMessageRoleFunction  = "function"
@@ -225,6 +226,13 @@ func (c *ChatCompletionMessageParamUnion) UnmarshalJSON(data []byte) error {
 		}
 		c.Value = systemMessage
 		c.Type = ChatMessageRoleSystem
+	case ChatMessageRoleDeveloper:
+		var developerMessage ChatCompletionDeveloperMessageParam
+		if err := json.Unmarshal(data, &developerMessage); err != nil {
+			return err
+		}
+		c.Value = developerMessage
+		c.Type = ChatMessageRoleDeveloper
 	case ChatMessageRoleTool:
 		var toolMessage ChatCompletionToolMessageParam
 		if err := json.Unmarshal(data, &toolMessage); err != nil {
@@ -263,6 +271,19 @@ type ChatCompletionSystemMessageParam struct {
 	Name string `json:"name,omitempty"`
 }
 
+// ChatCompletionDeveloperMessageParam Developer-provided instructions that the model should follow, regardless of
+// messages sent by the user. With o1 models and newer, use `developer` messages
+// for this purpose instead.
+type ChatCompletionDeveloperMessageParam struct {
+	// The contents of the developer message.
+	Content StringOrArray `json:"content"`
+	// The role of the messages author, in this case `developer`.
+	Role string `json:"role"`
+	// An optional name for the participant. Provides the model information to
+	// differentiate between participants of the same role.
+	Name string `json:"name,omitempty"`
+}
+
 type ChatCompletionToolMessageParam struct {
 	// The contents of the tool message.
 	Content StringOrArray `json:"content"`

internal/apischema/openai/openai_test.go

@@ -20,6 +20,7 @@ func TestOpenAIChatCompletionMessageUnmarshal(t *testing.T) {
 			in: []byte(`{"model": "gpu-o4",
                         "messages": [
                          {"role": "system", "content": "you are a helpful assistant"},
+                         {"role": "developer", "content": "you are a helpful dev assistant"},
                          {"role": "user", "content": "what do you see in this image"}]}`),
 			out: &ChatCompletionRequest{
 				Model: "gpu-o4",
@@ -33,6 +34,15 @@ func TestOpenAIChatCompletionMessageUnmarshal(t *testing.T) {
 						},
 						Type: ChatMessageRoleSystem,
 					},
+					{
+						Value: ChatCompletionDeveloperMessageParam{
+							Role: ChatMessageRoleDeveloper,
+							Content: StringOrArray{
+								Value: "you are a helpful dev assistant",
+							},
+						},
+						Type: ChatMessageRoleDeveloper,
+					},
 					{
 						Value: ChatCompletionUserMessageParam{
 							Role: ChatMessageRoleUser,
@@ -50,6 +60,7 @@ func TestOpenAIChatCompletionMessageUnmarshal(t *testing.T) {
 			in: []byte(`{"model": "gpu-o4",
                         "messages": [
                          {"role": "system", "content": [{"text": "you are a helpful assistant", "type": "text"}]},
+                         {"role": "developer", "content": [{"text": "you are a helpful dev assistant", "type": "text"}]},
                          {"role": "user", "content": [{"text": "what do you see in this image", "type": "text"}]}]}`),
 			out: &ChatCompletionRequest{
 				Model: "gpu-o4",
@@ -68,6 +79,20 @@ func TestOpenAIChatCompletionMessageUnmarshal(t *testing.T) {
 						},
 						Type: ChatMessageRoleSystem,
 					},
+					{
+						Value: ChatCompletionDeveloperMessageParam{
+							Role: ChatMessageRoleDeveloper,
+							Content: StringOrArray{
+								Value: []ChatCompletionContentPartTextParam{
+									{
+										Text: "you are a helpful dev assistant",
+										Type: string(openai.ChatCompletionContentPartTextTypeText),
+									},
+								},
+							},
+						},
+						Type: ChatMessageRoleDeveloper,
+					},
 					{
 						Value: ChatCompletionUserMessageParam{
 							Role: ChatMessageRoleUser,