Add DeepSeek integration support

internal/config/config.go

@@ -273,6 +273,9 @@ func setProviderDefaults() {
 	if apiKey := os.Getenv("XAI_API_KEY"); apiKey != "" {
 		viper.SetDefault("providers.xai.apiKey", apiKey)
 	}
+	if apiKey := os.Getenv("DEEPSEEK_API_KEY"); apiKey != "" {
+		viper.SetDefault("providers.deepseek.apiKey", apiKey)
+	}
 	if apiKey := os.Getenv("AZURE_OPENAI_ENDPOINT"); apiKey != "" {
 		// api-key may be empty when using Entra ID credentials – that's okay
 		viper.SetDefault("providers.azure.apiKey", os.Getenv("AZURE_OPENAI_API_KEY"))
@@ -358,6 +361,15 @@ func setProviderDefaults() {
 		return
 	}
 
+	// DeepSeek configuration
+	if key := viper.GetString("providers.deepseek.apiKey"); strings.TrimSpace(key) != "" {
+		viper.SetDefault("agents.coder.model", models.DeepSeekChat)
+		viper.SetDefault("agents.summarizer.model", models.DeepSeekChat)
+		viper.SetDefault("agents.task.model", models.DeepSeekChat)
+		viper.SetDefault("agents.title.model", models.DeepSeekChat)
+		return
+	}
+
 	// AWS Bedrock configuration
 	if hasAWSCredentials() {
 		viper.SetDefault("agents.coder.model", models.BedrockClaude37Sonnet)
@@ -663,6 +675,8 @@ func getProviderAPIKey(provider models.ModelProvider) string {
 		if hasVertexAICredentials() {
 			return "vertex-ai-credentials-available"
 		}
+	case models.ProviderDeepSeek:
+		return os.Getenv("DEEPSEEK_API_KEY")
 	}
 	return ""
 }

internal/llm/models/deepseek.go

@@ -0,0 +1,38 @@
+package models
+
+const (
+	ProviderDeepSeek ModelProvider = "deepseek"
+
+	DeepSeekChat     ModelID = "deepseek-chat"
+	DeepSeekReasoner ModelID = "deepseek-reasoner"
+)
+
+var DeepSeekModels = map[ModelID]Model{
+	DeepSeekChat: {
+		ID:                  DeepSeekChat,
+		Name:                "DeepSeek Chat",
+		Provider:            ProviderDeepSeek,
+		APIModel:            "deepseek-chat",
+		CostPer1MIn:         0.14,
+		CostPer1MInCached:   0.014,
+		CostPer1MOut:        0.28,
+		CostPer1MOutCached:  0.028,
+		ContextWindow:       163_840,
+		DefaultMaxTokens:    8192,
+		SupportsAttachments: true,
+	},
+	DeepSeekReasoner: {
+		ID:                  DeepSeekReasoner,
+		Name:                "DeepSeek Reasoner",
+		Provider:            ProviderDeepSeek,
+		APIModel:            "deepseek-reasoner",
+		CostPer1MIn:         0.55,
+		CostPer1MInCached:   0.055,
+		CostPer1MOut:        2.19,
+		CostPer1MOutCached:  0.219,
+		ContextWindow:       163_840,
+		DefaultMaxTokens:    8192,
+		CanReason:           true,
+		SupportsAttachments: true, // Reasoner supports tools!
+	},
+}

internal/llm/models/models.go

@@ -45,6 +45,7 @@ var ProviderPopularity = map[ModelProvider]int{
 	ProviderBedrock:    7,
 	ProviderAzure:      8,
 	ProviderVertexAI:   9,
+	ProviderDeepSeek:   10,
 }
 
 var SupportedModels = map[ModelID]Model{
@@ -95,4 +96,5 @@ func init() {
 	maps.Copy(SupportedModels, XAIModels)
 	maps.Copy(SupportedModels, VertexAIGeminiModels)
 	maps.Copy(SupportedModels, CopilotModels)
+	maps.Copy(SupportedModels, DeepSeekModels)
 }