Move common finish reasons to constants

- Create constants.go with FinishReasonStop, FinishReasonToolCalls, FinishReasonFunctionCall
- Replace all string literals with constants in chat.go, completion.go, realtime.go
- Improves code maintainability and prevents typos

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

Author: Copilot

core/http/endpoints/openai/chat.go

@@ -383,7 +383,7 @@ func ChatEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, evaluator
 						}
 						log.Error().Msgf("Stream ended with error: %v", err)
 
-						stopReason := "stop"
+						stopReason := FinishReasonStop
 						resp := &schema.OpenAIResponse{
 							ID:      id,
 							Created: created,
@@ -412,11 +412,11 @@ func ChatEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, evaluator
 					}
 				}
 
-				finishReason := "stop"
+				finishReason := FinishReasonStop
 				if toolsCalled && len(input.Tools) > 0 {
-					finishReason = "tool_calls"
+					finishReason = FinishReasonToolCalls
 				} else if toolsCalled {
-					finishReason = "function_call"
+					finishReason = FinishReasonFunctionCall
 				}
 
 				resp := &schema.OpenAIResponse{
@@ -448,7 +448,7 @@ func ChatEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, evaluator
 			tokenCallback := func(s string, c *[]schema.Choice) {
 				if !shouldUseFn {
 					// no function is called, just reply and use stop as finish reason
-					stopReason := "stop"
+					stopReason := FinishReasonStop
 					*c = append(*c, schema.Choice{FinishReason: &stopReason, Index: 0, Message: &schema.Message{Role: "assistant", Content: &s}})
 					return
 				}
@@ -467,12 +467,12 @@ func ChatEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, evaluator
 						return
 					}
 
-					stopReason := "stop"
+					stopReason := FinishReasonStop
 					*c = append(*c, schema.Choice{
 						FinishReason: &stopReason,
 						Message:      &schema.Message{Role: "assistant", Content: &result}})
 				default:
-					toolCallsReason := "tool_calls"
+					toolCallsReason := FinishReasonToolCalls
 					toolChoice := schema.Choice{
 						FinishReason: &toolCallsReason,
 						Message: &schema.Message{
@@ -498,7 +498,7 @@ func ChatEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, evaluator
 							)
 						} else {
 							// otherwise we return more choices directly (deprecated)
-							functionCallReason := "function_call"
+							functionCallReason := FinishReasonFunctionCall
 							*c = append(*c, schema.Choice{
 								FinishReason: &functionCallReason,
 								Message: &schema.Message{

core/http/endpoints/openai/completion.go

@@ -155,7 +155,7 @@ func CompletionEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, eva
 						}
 						log.Error().Msgf("Stream ended with error: %v", err)
 
-						stopReason := "stop"
+						stopReason := FinishReasonStop
 						errorResp := schema.OpenAIResponse{
 							ID:      id,
 							Created: created,
@@ -182,7 +182,7 @@ func CompletionEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, eva
 					}
 				}
 
-				stopReason := "stop"
+				stopReason := FinishReasonStop
 				resp := &schema.OpenAIResponse{
 					ID:      id,
 					Created: created,
@@ -222,7 +222,7 @@ func CompletionEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, eva
 
 			r, tokenUsage, err := ComputeChoices(
 				input, i, config, cl, appConfig, ml, func(s string, c *[]schema.Choice) {
-					stopReason := "stop"
+					stopReason := FinishReasonStop
 					*c = append(*c, schema.Choice{Text: s, FinishReason: &stopReason, Index: k})
 				}, nil)
 			if err != nil {

core/http/endpoints/openai/constants.go

@@ -0,0 +1,8 @@
+package openai
+
+// Finish reason constants for OpenAI API responses
+const (
+	FinishReasonStop         = "stop"
+	FinishReasonToolCalls    = "tool_calls"
+	FinishReasonFunctionCall = "function_call"
+)

core/http/endpoints/openai/realtime.go

@@ -1072,7 +1072,7 @@ func processTextResponse(config *config.ModelConfig, session *Session, prompt st
 		result, tokenUsage, err := ComputeChoices(input, prompt, config, startupOptions, ml, func(s string, c *[]schema.Choice) {
 			if !shouldUseFn {
 				// no function is called, just reply and use stop as finish reason
-				stopReason := "stop"
+				stopReason := FinishReasonStop
 				*c = append(*c, schema.Choice{FinishReason: &stopReason, Index: 0, Message: &schema.Message{Role: "assistant", Content: &s}})
 				return
 			}
@@ -1100,7 +1100,8 @@ func processTextResponse(config *config.ModelConfig, session *Session, prompt st
 				}
 
 				if len(input.Tools) > 0 {
-					toolChoice.FinishReason = "tool_calls"
+					toolCallsReason := FinishReasonToolCalls
+					toolChoice.FinishReason = &toolCallsReason
 				}
 
 				for _, ss := range results {
@@ -1121,7 +1122,7 @@ func processTextResponse(config *config.ModelConfig, session *Session, prompt st
 						)
 					} else {
 						// otherwise we return more choices directly
-						functionCallReason := "function_call"
+						functionCallReason := FinishReasonFunctionCall
 						*c = append(*c, schema.Choice{
 							FinishReason: &functionCallReason,
 							Message: &schema.Message{