fix: correct deepseek pricing, gemini streaming tokens, and group-name logging

- Add promo discount system for deepseek-v4-pro (75% off until 2026-05-31)
- Rewrite StreamGemini to handle both SSE and JSON array response formats,
  fixing 0-token logging for gemini-3-flash and gemini-3-flash-preview
- Fall back to model group name for cost lookup when concrete model
  isnt in the registry (fixes $0 cost on deepseek-auto entries)
- Move registry lock before FindModel call to fix data race

internal/providers/gemini.go

@@ -621,16 +621,10 @@ func (p *GeminiProvider) ChatCompletionStream(ctx context.Context, req *models.U
 		return nil, fmt.Errorf("Gemini API error (%d): %s", resp.StatusCode(), msg)
 	}
 
-	ch := make(chan *models.ChatCompletionStreamResponse)
-
-	go func() {
-		defer close(ch)
-		err := StreamGemini(resp.RawBody(), ch, req.Model)
+	ch, err := StreamGemini(resp.RawBody(), req.Model)
 	if err != nil {
-			fmt.Printf("Gemini Stream error: %v\n", err)
+		return nil, fmt.Errorf("gemini stream init error: %w", err)
 	}
-	}()
-
 	return ch, nil
 }
 

internal/providers/helpers.go

@@ -364,18 +364,8 @@ func StreamOpenAI(ctx io.ReadCloser, ch chan<- *models.ChatCompletionStreamRespo
 	return scanner.Err()
 }
 
-func StreamGemini(ctx io.ReadCloser, ch chan<- *models.ChatCompletionStreamResponse, model string) error {
-	defer ctx.Close()
-
-	dec := json.NewDecoder(ctx)
-
-	t, err := dec.Token()
-	if err != nil {
-		return err
-	}
-	if delim, ok := t.(json.Delim); ok && delim == '[' {
-		for dec.More() {
-			var geminiChunk struct {
+// geminiStreamChunk is the shared data structure for parsing Gemini streaming responses.
+type geminiStreamChunk struct {
 	Candidates []struct {
 		Content struct {
 			Parts []struct {
@@ -393,15 +383,18 @@ func StreamGemini(ctx io.ReadCloser, ch chan<- *models.ChatCompletionStreamRespo
 	} `json:"usageMetadata"`
 }
 
-			if err := dec.Decode(&geminiChunk); err != nil {
-				return err
+// emitGeminiChunk builds a ChatCompletionStreamResponse from a parsed geminiStreamChunk
+// and sends it to the channel. Returns true if anything was emitted.
+func emitGeminiChunk(ch chan<- *models.ChatCompletionStreamResponse, chunk *geminiStreamChunk, model string) bool {
+	if len(chunk.Candidates) == 0 && chunk.UsageMetadata.TotalTokenCount == 0 {
+		return false
 	}
 
-			if len(geminiChunk.Candidates) > 0 || geminiChunk.UsageMetadata.TotalTokenCount > 0 {
 	content := ""
 	var reasoning *string
-				if len(geminiChunk.Candidates) > 0 {
-					for _, p := range geminiChunk.Candidates[0].Content.Parts {
+	var finishReason *string
+	if len(chunk.Candidates) > 0 {
+		for _, p := range chunk.Candidates[0].Content.Parts {
 			if p.Text != "" {
 				content += p.Text
 			}
@@ -412,11 +405,7 @@ func StreamGemini(ctx io.ReadCloser, ch chan<- *models.ChatCompletionStreamRespo
 				*reasoning += p.Thought
 			}
 		}
-				}
-
-				var finishReason *string
-				if len(geminiChunk.Candidates) > 0 {
-					fr := strings.ToLower(geminiChunk.Candidates[0].FinishReason)
+		fr := strings.ToLower(chunk.Candidates[0].FinishReason)
 		finishReason = &fr
 	}
 
@@ -436,17 +425,141 @@ func StreamGemini(ctx io.ReadCloser, ch chan<- *models.ChatCompletionStreamRespo
 			},
 		},
 		Usage: &models.Usage{
-						PromptTokens:     geminiChunk.UsageMetadata.PromptTokenCount,
-						CompletionTokens: geminiChunk.UsageMetadata.CandidatesTokenCount,
-						TotalTokens:      geminiChunk.UsageMetadata.TotalTokenCount,
-						CacheReadTokens:  uint32Ptr(geminiChunk.UsageMetadata.CachedContentTokenCount),
+			PromptTokens:     chunk.UsageMetadata.PromptTokenCount,
+			CompletionTokens: chunk.UsageMetadata.CandidatesTokenCount,
+			TotalTokens:      chunk.UsageMetadata.TotalTokenCount,
+			CacheReadTokens:  uint32Ptr(chunk.UsageMetadata.CachedContentTokenCount),
 		},
 	}
+	return true
 }
+
+// StreamGemini handles Gemini streaming responses in two formats:
+//  1. SSE format (newer models): each line is "data: {...}"
+//  2. JSON array format (older models): response body is [ {...}, {...} ]
+//
+// Usage metadata is only present in the final chunk, which we accumulate
+// and emit so the server can log it on stream end.
+func StreamGemini(ctx io.ReadCloser, model string) (<-chan *models.ChatCompletionStreamResponse, error) {
+	ch := make(chan *models.ChatCompletionStreamResponse)
+
+	go func() {
+		defer func() {
+			_ = ctx.Close()
+		}()
+		defer close(ch)
+
+		// Peek at the first byte to detect format
+		peek := make([]byte, 6)
+		n, _ := io.ReadAtLeast(ctx, peek, 1)
+		if n == 0 {
+			return
+		}
+
+		first := string(peek[:n])
+
+		if first[0] == '[' {
+			// JSON array format
+			rest, _ := io.ReadAll(ctx)
+			streamGeminiJSONArray(append([]byte(first), rest...), ch, model)
+			return
+		} else if strings.HasPrefix(first, "data:") || strings.HasPrefix(first, "data: ") {
+			// SSE format — pre-pend the peeked bytes then run SSE scanner
+			combined := io.MultiReader(
+				strings.NewReader(string(peek[:n])),
+				ctx,
+			)
+			streamGeminiSSE(combined, ch, model)
+		} else {
+			// Unknown format — might still be SSE starting after a peek char
+			// Pre-pend peeked bytes and try SSE
+			combined := io.MultiReader(
+				strings.NewReader(string(peek[:n])),
+				ctx,
+			)
+			streamGeminiSSE(combined, ch, model)
+		}
+	}()
+
+	return ch, nil
+}
+
+// readAll reads remaining bytes from a reader (keeps the function signature simple
+// for the JSON array fallback path).
+func readAll(r io.Reader) []byte {
+	b, _ := io.ReadAll(r)
+	return b
+}
+
+func streamGeminiJSONArray(data []byte, ch chan<- *models.ChatCompletionStreamResponse, model string) {
+	var chunks []geminiStreamChunk
+	if err := json.Unmarshal(data, &chunks); err != nil {
+		fmt.Printf("[Gemini-Stream] JSON array parse error: %v\n", err)
+		return
+	}
+	// Track the last chunk with usage for the final emission
+	var lastUsage *geminiStreamChunk
+	for i := range chunks {
+		if chunks[i].UsageMetadata.TotalTokenCount > 0 {
+			lastUsage = &chunks[i]
+		}
+	}
+	if lastUsage != nil {
+		// Emit a synthetic final chunk with usage data
+		if len(lastUsage.Candidates) == 0 && lastUsage.UsageMetadata.TotalTokenCount > 0 {
+			emitGeminiChunk(ch, lastUsage, model)
+		}
+	}
+	// Also emit each content-bearing chunk
+	for i := range chunks {
+		emitGeminiChunk(ch, &chunks[i], model)
 	}
 }
 
-	return nil
+func streamGeminiSSE(r io.Reader, ch chan<- *models.ChatCompletionStreamResponse, model string) {
+	scanner := bufio.NewScanner(r)
+	// Track the last seen usage for emission at end of stream
+	var lastUsage geminiStreamChunk
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" || !strings.HasPrefix(line, "data: ") {
+			continue
+		}
+
+		data := strings.TrimPrefix(line, "data: ")
+		if data == "[DONE]" {
+			// Emit final usage if we have one
+			if lastUsage.UsageMetadata.TotalTokenCount > 0 {
+				emitGeminiChunk(ch, &lastUsage, model)
+			}
+			break
+		}
+
+		var chunk geminiStreamChunk
+		if err := json.Unmarshal([]byte(data), &chunk); err != nil {
+			continue
+		}
+
+		// Capture usage from any chunk (Gemini puts it in the final response)
+		if chunk.UsageMetadata.TotalTokenCount > 0 {
+			lastUsage = chunk
+		}
+
+		// Emit content chunks as they arrive
+		if len(chunk.Candidates) > 0 {
+			emitGeminiChunk(ch, &chunk, model)
+		}
+	}
+
+	// If stream ended without [DONE] marker but we collected usage, emit it
+	if lastUsage.UsageMetadata.TotalTokenCount > 0 {
+		emitGeminiChunk(ch, &lastUsage, model)
+	}
+
+	if err := scanner.Err(); err != nil {
+		fmt.Printf("[Gemini-Stream] SSE scan error: %v\n", err)
+	}
 }
 
 // ensureEnglish injects a system message instructing the model to respond in

internal/server/server.go

@@ -309,9 +309,32 @@ func (s *Server) handleResponses(c *gin.Context) {
 		return
 	}
 
-	// Select provider based on model name
+	// Strip common prefixes and resolve model groups to concrete models
+	// (same pattern as handleChatCompletions).
+	modelGroup := ""
+	modelID := req.Model
+	prefixes := []string{"gemini/", "google/", "openai/", "deepseek/", "moonshot/", "grok/", "ollama/"}
+	for _, p := range prefixes {
+		if strings.HasPrefix(modelID, p) {
+			modelID = strings.TrimPrefix(modelID, p)
+			break
+		}
+	}
+	if s.modelRouter != nil {
+		decision, err := s.modelRouter.RouteToConcrete(c.Request.Context(), modelID, "")
+		if err != nil {
+			c.JSON(http.StatusInternalServerError, gin.H{"error": fmt.Sprintf("model routing failed: %v", err)})
+			return
+		}
+		if decision.SelectedModel != modelID {
+			modelGroup = modelID
+		}
+		modelID = decision.SelectedModel
+	}
+
+	// Select provider based on resolved model name
 	providerName := "openai" // default for Responses API
-	modelLower := strings.ToLower(req.Model)
+	modelLower := strings.ToLower(modelID)
 	if strings.HasPrefix(modelLower, "gemini/") || strings.Contains(modelLower, "gemini") || strings.HasPrefix(modelLower, "google/") {
 		providerName = "gemini"
 	} else if strings.HasPrefix(modelLower, "deepseek/") || (strings.Contains(modelLower, "deepseek") && !strings.Contains(modelLower, "ollama")) {
@@ -339,17 +362,7 @@ func (s *Server) handleResponses(c *gin.Context) {
 		return
 	}
 
-	// Strip common prefixes from model name
-	modelID := req.Model
-	prefixes := []string{"gemini/", "google/", "openai/", "deepseek/", "moonshot/", "grok/", "ollama/"}
-	for _, p := range prefixes {
-		if strings.HasPrefix(modelID, p) {
-			modelID = strings.TrimPrefix(modelID, p)
-			break
-		}
-	}
-
-	// Use the stripped model name for the actual API call
+	// Use resolved model for the actual API call
 	req.Model = modelID
 
 	clientID := "default"
@@ -364,7 +377,7 @@ func (s *Server) handleResponses(c *gin.Context) {
 	if stream {
 		ch, err := provider.ResponsesStream(c.Request.Context(), &req)
 		if err != nil {
-			s.logRequest(startTime, clientID, providerName, req.Model, "", nil, err, false)
+			s.logRequest(startTime, clientID, providerName, modelID, modelGroup, nil, err, false)
 			c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
 			return
 		}
@@ -379,9 +392,9 @@ func (s *Server) handleResponses(c *gin.Context) {
 			if !ok {
 				fmt.Fprintf(w, "data: [DONE]\n\n")
 				if lastUsage != nil {
-					s.logRequest(startTime, clientID, providerName, req.Model, "", lastUsage.ToUsage(), nil, false)
+					s.logRequest(startTime, clientID, providerName, modelID, modelGroup, lastUsage.ToUsage(), nil, false)
 				} else {
-					s.logRequest(startTime, clientID, providerName, req.Model, "", nil, nil, false)
+					s.logRequest(startTime, clientID, providerName, modelID, modelGroup, nil, nil, false)
 				}
 				return false
 			}
@@ -401,15 +414,15 @@ func (s *Server) handleResponses(c *gin.Context) {
 
 	resp, err := provider.Responses(c.Request.Context(), &req)
 	if err != nil {
-		s.logRequest(startTime, clientID, providerName, req.Model, "", nil, err, false)
+		s.logRequest(startTime, clientID, providerName, modelID, modelGroup, nil, err, false)
 		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
 		return
 	}
 
 	if resp.Usage != nil {
-		s.logRequest(startTime, clientID, providerName, req.Model, "", resp.Usage.ToUsage(), nil, false)
+		s.logRequest(startTime, clientID, providerName, modelID, modelGroup, resp.Usage.ToUsage(), nil, false)
 	} else {
-		s.logRequest(startTime, clientID, providerName, req.Model, "", nil, nil, false)
+		s.logRequest(startTime, clientID, providerName, modelID, modelGroup, nil, nil, false)
 	}
 	c.JSON(http.StatusOK, resp)
 }
@@ -881,9 +894,14 @@ func (s *Server) logRequest(start time.Time, clientID, provider, model, modelGro
 			entry.CacheWriteTokens = *usage.CacheWriteTokens
 		}
 
-		// Calculate cost using registry
+		// Calculate cost using registry; if the resolved model is unknown,
+		// fall back to the model group so group requests still get priced.
 		s.registryMu.RLock()
-		entry.Cost = utils.CalculateCost(s.registry, model, entry.PromptTokens, entry.CompletionTokens, entry.ReasoningTokens, entry.CacheReadTokens, entry.CacheWriteTokens)
+		pricingModel := model
+		if s.registry != nil && s.registry.FindModel(pricingModel) == nil && modelGroup != "" {
+			pricingModel = modelGroup
+		}
+		entry.Cost = utils.CalculateCost(s.registry, pricingModel, entry.PromptTokens, entry.CompletionTokens, entry.ReasoningTokens, entry.CacheReadTokens, entry.CacheWriteTokens)
 		s.registryMu.RUnlock()
 	}
 

internal/utils/registry.go

@@ -45,6 +45,24 @@ func FetchRegistry() (*models.ModelRegistry, error) {
 	return nil, fmt.Errorf("failed to fetch registry after 3 attempts: %w", lastErr)
 }
 
+// promoDiscount describes a temporary pricing discount applied on top of
+// the standard (list) price from the model registry.
+type promoDiscount struct {
+	Factor    float64   // multiplier applied after standard calculation (0.25 = 75% off)
+	ExpiresAt time.Time // discount ends at this time (UTC)
+}
+
+// promoDiscounts maps model IDs to active promotional discounts.
+// Sources:
+//   - DeepSeek v4 Pro: 75% off list pricing until 2026-05-31
+//     https://api-docs.deepseek.com/quick_start/pricing
+var promoDiscounts = map[string]promoDiscount{
+	"deepseek-v4-pro": {
+		Factor:    0.25,
+		ExpiresAt: time.Date(2026, 5, 31, 23, 59, 59, 0, time.UTC),
+	},
+}
+
 func CalculateCost(registry *models.ModelRegistry, modelID string, promptTokens, completionTokens, reasoningTokens, cacheRead, cacheWrite uint32) float64 {
 	meta := registry.FindModel(modelID)
 	if meta == nil || meta.Cost == nil {
@@ -72,5 +90,12 @@ func CalculateCost(registry *models.ModelRegistry, modelID string, promptTokens,
 		cost += float64(cacheWrite) * (*meta.Cost.CacheWrite) / 1000000.0
 	}
 
+	// Apply promotional discounts (e.g. DeepSeek 75% off until 2026-05-31).
+	if discount, ok := promoDiscounts[modelID]; ok {
+		if time.Now().UTC().Before(discount.ExpiresAt) {
+			cost *= discount.Factor
+		}
+	}
+
 	return cost
 }