Enable streaming UI updates for chat responses

internal/openai/types.go

@@ -37,6 +37,19 @@ type ChatCompletionResponse struct {
 	Usage   Usage                  `json:"usage"`
 }
 
+// ChatCompletionStreamEvent represents a single chunk in a streaming chat completion.
+type ChatCompletionStreamEvent struct {
+	ID           string `json:"-"`
+	Role         string `json:"-"`
+	Content      string `json:"-"`
+	FinishReason string `json:"-"`
+	Usage        *Usage `json:"-"`
+	Done         bool   `json:"-"`
+}
+
+// ChatCompletionStreamHandler consumes streaming completion events.
+type ChatCompletionStreamHandler func(ChatCompletionStreamEvent) error
+
 // APIError captures structured error responses returned by the API.
 type APIError struct {
 	Message string `json:"message"`