fix(go): fixed system/messages/user order in prompts (#3812)

Author: apascal07

go/ai/prompt.go

@@ -182,10 +182,26 @@ func (p *prompt) Execute(ctx context.Context, opts ...PromptExecuteOption) (*Mod
 			},
 		}
 
-		actionOpts.Messages, err = renderMessages(ctx, tempOpts, actionOpts.Messages, m, execOpts.Input, p.registry.Dotprompt())
+		execMsgs, err := renderMessages(ctx, tempOpts, []*Message{}, m, execOpts.Input, p.registry.Dotprompt())
 		if err != nil {
 			return nil, err
 		}
+
+		var systemMsgs []*Message
+		var msgs []*Message
+		foundNonSystem := false
+
+		for _, msg := range actionOpts.Messages {
+			if msg.Role == RoleSystem && !foundNonSystem {
+				systemMsgs = append(systemMsgs, msg)
+			} else {
+				foundNonSystem = true
+				msgs = append(msgs, msg)
+			}
+		}
+
+		actionOpts.Messages = append(systemMsgs, execMsgs...)
+		actionOpts.Messages = append(actionOpts.Messages, msgs...)
 	}
 
 	toolRefs := execOpts.Tools

go/ai/prompt_test.go

@@ -511,7 +511,7 @@ func TestValidPrompt(t *testing.T) {
 				WithInput(HelloPromptInput{Name: "foo"}),
 				WithMessages(NewModelTextMessage("I remember you said your name is {{Name}}")),
 			},
-			wantTextOutput: "Echo: system: say hello; my name is foo; I remember you said your name is foo; config: {\n  \"temperature\": 11\n}; context: null",
+			wantTextOutput: "Echo: system: say hello; I remember you said your name is foo; my name is foo; config: {\n  \"temperature\": 11\n}; context: null",
 			wantGenerated: &ModelRequest{
 				Config: &GenerationCommonConfig{
 					Temperature: 11,
@@ -525,14 +525,14 @@ func TestValidPrompt(t *testing.T) {
 						Role:    RoleSystem,
 						Content: []*Part{NewTextPart("say hello")},
 					},
-					{
-						Role:    RoleUser,
-						Content: []*Part{NewTextPart("my name is foo")},
-					},
 					{
 						Role:    RoleModel,
 						Content: []*Part{NewTextPart("I remember you said your name is foo")},
 					},
+					{
+						Role:    RoleUser,
+						Content: []*Part{NewTextPart("my name is foo")},
+					},
 				},
 			},
 		},