feat: Add system prompt configuration support (#26)

This PR implements system prompt configuration for the Inference Gateway
CLI as requested in issue #25.

## Changes

- Add `system_prompt` field to ChatConfig in config structure
- Implement `infer config set-system` command for setting system prompts
- Update chat service to include system prompt in API messages
- Modify service container to pass system prompt to chat service
- Update documentation with new command and configuration examples

## Usage

```bash
# Set a system prompt
infer config set-system "You are a helpful assistant."

# The system prompt is now included with every chat session
infer chat
```

The system prompt is configurable via command or by modifying the config
directly and is included in SDK messages as a system prompt.

Resolves #25

Generated with [Claude Code](https://claude.ai/code)

---------

Signed-off-by: Eden Reich <[email protected]>
Co-authored-by: claude[bot] <209825114+claude[bot]@users.noreply.github.com>
Co-authored-by: Eden Reich <[email protected]>

Author: edenreich

.infer/config.yaml

@@ -31,3 +31,4 @@ compact:
   output_dir: .infer
 chat:
   default_model: ""
+  system_prompt: ""

CLAUDE.md

@@ -159,6 +159,7 @@ compact:
   output_dir: ".infer"  # Directory for compact command exports (default: project root/.infer)
 chat:
   default_model: ""  # Default model for chat sessions (when set, skips model selection)
+  system_prompt: ""  # System prompt included with every chat session
 ```
 
 ### Command Structure
@@ -170,6 +171,7 @@ chat:
   - `config`: Manage CLI configuration
     - `init [--overwrite]`: Initialize local project configuration
     - `set-model [MODEL_NAME]`: Set default model for chat sessions
+    - `set-system [SYSTEM_PROMPT]`: Set system prompt for chat sessions
     - `tools`: Manage tool execution settings
       - `enable`: Enable tool execution for LLMs
       - `disable`: Disable tool execution for LLMs
@@ -212,6 +214,16 @@ infer config set-model gpt-4-turbo
 infer chat
 ```
 
+### Setting a System Prompt
+```bash
+# Set a system prompt for chat sessions
+infer config set-system "You are a helpful assistant."
+
+# The system prompt will now be included with every chat session
+# providing context and instructions to the AI model
+infer chat
+```
+
 ### Configuration Management
 ```bash
 # Initialize a new project configuration
@@ -223,9 +235,10 @@ infer config init --overwrite
 # View current configuration (check .infer/config.yaml)
 cat .infer/config.yaml
 
-# The default model will be saved in the chat section:
+# The default model and system prompt will be saved in the chat section:
 # chat:
 #   default_model: "gpt-4-turbo"
+#   system_prompt: "You are a helpful assistant."
 ```
 
 ### Tool Management

cmd/config.go

@@ -31,6 +31,18 @@ the chat command will skip the model selection view and use the configured model
 	},
 }
 
+var setSystemCmd = &cobra.Command{
+	Use:   "set-system [SYSTEM_PROMPT]",
+	Short: "Set the system prompt for chat sessions",
+	Long: `Set the system prompt that will be included with every chat session.
+The system prompt provides context and instructions to the AI model about how to behave.`,
+	Args: cobra.ExactArgs(1),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		systemPrompt := args[0]
+		return setSystemPrompt(systemPrompt)
+	},
+}
+
 var configInitCmd = &cobra.Command{
 	Use:   "init",
 	Short: "Initialize a new project configuration",
@@ -176,8 +188,27 @@ func setDefaultModel(modelName string) error {
 	return nil
 }
 
+func setSystemPrompt(systemPrompt string) error {
+	cfg, err := config.LoadConfig("")
+	if err != nil {
+		return fmt.Errorf("failed to load config: %w", err)
+	}
+
+	cfg.Chat.SystemPrompt = systemPrompt
+
+	if err := cfg.SaveConfig(""); err != nil {
+		return fmt.Errorf("failed to save config: %w", err)
+	}
+
+	fmt.Printf("✅ System prompt set successfully\n")
+	fmt.Printf("System prompt: %s\n", systemPrompt)
+	fmt.Println("This prompt will be included with every chat session.")
+	return nil
+}
+
 func init() {
 	configCmd.AddCommand(setModelCmd)
+	configCmd.AddCommand(setSystemCmd)
 	configCmd.AddCommand(configInitCmd)
 	configCmd.AddCommand(configToolsCmd)
 

config/config.go

@@ -59,6 +59,7 @@ type CompactConfig struct {
 // ChatConfig contains chat-related settings
 type ChatConfig struct {
 	DefaultModel string `yaml:"default_model"`
+	SystemPrompt string `yaml:"system_prompt"`
 }
 
 // DefaultConfig returns a default configuration
@@ -100,6 +101,7 @@ func DefaultConfig() *Config {
 		},
 		Chat: ChatConfig{
 			DefaultModel: "",
+			SystemPrompt: "",
 		},
 	}
 }

internal/container/container.go

@@ -68,6 +68,7 @@ func (c *ServiceContainer) initializeDomainServices() {
 		c.config.Gateway.APIKey,
 		c.config.Gateway.Timeout,
 		c.toolService,
+		c.config.Chat.SystemPrompt,
 	)
 }
 

internal/services/chat.go

@@ -20,6 +20,7 @@ type StreamingChatService struct {
 	timeoutSeconds int
 	client         sdk.Client
 	toolService    domain.ToolService
+	systemPrompt   string
 
 	// Request tracking
 	activeRequests map[string]context.CancelFunc
@@ -31,7 +32,7 @@ type StreamingChatService struct {
 }
 
 // NewStreamingChatService creates a new streaming chat service
-func NewStreamingChatService(baseURL, apiKey string, timeoutSeconds int, toolService domain.ToolService) *StreamingChatService {
+func NewStreamingChatService(baseURL, apiKey string, timeoutSeconds int, toolService domain.ToolService, systemPrompt string) *StreamingChatService {
 	if !strings.HasSuffix(baseURL, "/v1") {
 		baseURL = strings.TrimSuffix(baseURL, "/") + "/v1"
 	}
@@ -47,6 +48,7 @@ func NewStreamingChatService(baseURL, apiKey string, timeoutSeconds int, toolSer
 		timeoutSeconds: timeoutSeconds,
 		client:         client,
 		toolService:    toolService,
+		systemPrompt:   systemPrompt,
 		activeRequests: make(map[string]context.CancelFunc),
 		metrics:        make(map[string]*domain.ChatMetrics),
 	}
@@ -78,13 +80,26 @@ func (s *StreamingChatService) validateSendMessageParams(model string, messages
 }
 
 func (s *StreamingChatService) addToolsIfAvailable(messages []sdk.Message) []sdk.Message {
+	var systemMessages []sdk.Message
+
+	if s.systemPrompt != "" {
+		systemMessages = append(systemMessages, sdk.Message{
+			Role:    sdk.System,
+			Content: s.systemPrompt,
+		})
+	}
+
 	if s.toolService != nil {
 		availableTools := s.toolService.ListTools()
 		if len(availableTools) > 0 {
 			toolsMessage := s.createToolsSystemMessage(availableTools)
-			messages = append([]sdk.Message{toolsMessage}, messages...)
+			systemMessages = append(systemMessages, toolsMessage)
 		}
 	}
+
+	if len(systemMessages) > 0 {
+		messages = append(systemMessages, messages...)
+	}
 	return messages
 }