fix: remove tool call ID truncation and improve DeepSeek reasoning handling

The 40-character truncation of tool call IDs in helper.go caused collisions
when models (like deepseek-v4-flash) generated longer IDs, leading to
"Duplicate value for 'tool_call_id'" errors. Removed the limit to allow
full unique IDs.

DeepSeek: updated reasoning_content injection to use an empty string
instead of a space, better matching provider expectations for history.

Improved API error reporting across all providers by capturing raw body
content when response parsing fails or returns empty strings.

internal/providers/deepseek.go

@@ -72,19 +72,26 @@ func (p *DeepSeekProvider) ChatCompletion(ctx context.Context, req *models.Unifi
 
 	body := BuildOpenAIBody(req, messagesJSON, false)
 
-	// Sanitize for deepseek-reasoner
-	if req.Model == "deepseek-reasoner" {
-		delete(body, "temperature")
-		delete(body, "top_p")
-		delete(body, "presence_penalty")
-		delete(body, "frequency_penalty")
+	// Sanitize for models that support reasoning/thinking mode
+	isReasoner := strings.Contains(req.Model, "reasoner") || strings.Contains(req.Model, "v4") || strings.Contains(req.Model, "r1")
+
+	if isReasoner {
+		// deepseek-reasoner (R1) does not support these parameters
+		if req.Model == "deepseek-reasoner" || strings.HasPrefix(req.Model, "deepseek-r1") {
+			delete(body, "temperature")
+			delete(body, "top_p")
+			delete(body, "presence_penalty")
+			delete(body, "frequency_penalty")
+		}
 
 		if msgs, ok := body["messages"].([]interface{}); ok {
 			for _, m := range msgs {
 				if msg, ok := m.(map[string]interface{}); ok {
 					if msg["role"] == "assistant" {
+						// DeepSeek requires reasoning_content to be passed back in history
+						// if the model is in thinking mode.
 						if msg["reasoning_content"] == nil {
-							msg["reasoning_content"] = " "
+							msg["reasoning_content"] = ""
 						}
 						if msg["content"] == nil || msg["content"] == "" {
 							msg["content"] = ""
@@ -106,7 +113,15 @@ func (p *DeepSeekProvider) ChatCompletion(ctx context.Context, req *models.Unifi
 	}
 
 	if !resp.IsSuccess() {
-		return nil, fmt.Errorf("DeepSeek API error (%d): %s", resp.StatusCode(), resp.String())
+		var msg string
+		if resp.RawBody() != nil {
+			bodyBytes, _ := io.ReadAll(resp.RawBody())
+			msg = string(bodyBytes)
+		}
+		if msg == "" {
+			msg = resp.String()
+		}
+		return nil, fmt.Errorf("DeepSeek API error (%d): %s", resp.StatusCode(), msg)
 	}
 
 	var respJSON map[string]interface{}
@@ -141,19 +156,26 @@ func (p *DeepSeekProvider) ChatCompletionStream(ctx context.Context, req *models
 
 	body := BuildOpenAIBody(req, messagesJSON, true)
 
-	// Sanitize for deepseek-reasoner
-	if req.Model == "deepseek-reasoner" {
-		delete(body, "temperature")
-		delete(body, "top_p")
-		delete(body, "presence_penalty")
-		delete(body, "frequency_penalty")
+	// Sanitize for models that support reasoning/thinking mode
+	isReasoner := strings.Contains(req.Model, "reasoner") || strings.Contains(req.Model, "v4") || strings.Contains(req.Model, "r1")
+
+	if isReasoner {
+		// deepseek-reasoner (R1) does not support these parameters
+		if req.Model == "deepseek-reasoner" || strings.HasPrefix(req.Model, "deepseek-r1") {
+			delete(body, "temperature")
+			delete(body, "top_p")
+			delete(body, "presence_penalty")
+			delete(body, "frequency_penalty")
+		}
 
 		if msgs, ok := body["messages"].([]interface{}); ok {
 			for _, m := range msgs {
 				if msg, ok := m.(map[string]interface{}); ok {
 					if msg["role"] == "assistant" {
+						// DeepSeek requires reasoning_content to be passed back in history
+						// if the model is in thinking mode.
 						if msg["reasoning_content"] == nil {
-							msg["reasoning_content"] = " "
+							msg["reasoning_content"] = ""
 						}
 						if msg["content"] == nil || msg["content"] == "" {
 							msg["content"] = ""
@@ -176,7 +198,15 @@ func (p *DeepSeekProvider) ChatCompletionStream(ctx context.Context, req *models
 	}
 
 	if !resp.IsSuccess() {
-		return nil, fmt.Errorf("DeepSeek API error (%d): %s", resp.StatusCode(), resp.String())
+		var msg string
+		if resp.RawBody() != nil {
+			bodyBytes, _ := io.ReadAll(resp.RawBody())
+			msg = string(bodyBytes)
+		}
+		if msg == "" {
+			msg = resp.String()
+		}
+		return nil, fmt.Errorf("DeepSeek API error (%d): %s", resp.StatusCode(), msg)
 	}
 
 	ch := make(chan *models.ChatCompletionStreamResponse)