feat: add comprehensive config validation at startup

- Add Validate() method to check all config fields, formats, and inter-dependencies
- Add validation for all major config areas: agents, channels, gateway, tools, model_list, heartbeat, devices
- Integrate validation into LoadConfig() to catch errors at startup
- Add custom isValidName() function to validate identifiers
- Update AgentDefaults with missing MaxMediaSize field
- Add tests for config validation functionality

This adds a robust validation layer that will catch misconfigurations
before runtime, preventing many potential configuration-related bugs

🤖 AI Assisted - Human designed the solution, AI helped implement it

pkg/config/config.go

@@ -1363,7 +1363,7 @@ func isValidName(name string) bool {
 	}
 
 	// Avoid certain reserved names that shouldn't be used as identifiers
-	reserved := map[string]bool{"", ".", "..", "nil"}
+	reserved := map[string]bool{"": true, ".": true, "..": true, "nil": true}
 	if reserved[name] || strings.TrimSpace(name) != name {
 		return false
 	}

pkg/config/validation_test.go

@@ -0,0 +1,106 @@
+package config
+
+import (
+	"testing"
+)
+
+func TestConfigValidation_Comprehensive(t *testing.T) {
+	// Test valid configuration
+	validConfig := &Config{
+		Agents: AgentsConfig{
+			Defaults: AgentDefaults{
+				Workspace: "~/test-workspace",
+				Model:     "test-model",
+			},
+		},
+		Channels: ChannelsConfig{
+			Telegram: TelegramConfig{
+				Enabled: false, // Disabled, so no token required
+			},
+		},
+		Gateway: GatewayConfig{
+			Host: "localhost",
+			Port: 8080,
+		},
+		ModelList: []ModelConfig{
+			{
+				ModelName: "test-model",
+				Model:     "openai/gpt-test",
+			},
+		},
+	}
+
+	if err := validConfig.Validate(); err != nil {
+		t.Errorf("Valid config should not produce validation error, but got: %v", err)
+	}
+
+	// Test invalid configuration - missing workspace
+	invalidConfig := &Config{
+		Agents: AgentsConfig{
+			Defaults: AgentDefaults{
+				Workspace: "", // Missing required field
+			},
+		},
+		Channels: ChannelsConfig{
+			Telegram: TelegramConfig{
+				Enabled: false,
+			},
+		},
+		Gateway: GatewayConfig{
+			Host: "localhost",
+			Port: 8080,
+		},
+		ModelList: []ModelConfig{
+			{
+				ModelName: "test-model",
+				Model:     "openai/gpt-test",
+			},
+		},
+	}
+
+	if err := invalidConfig.Validate(); err == nil {
+		t.Error("Invalid config (missing workspace) should produce validation error, but didn't get one")
+	}
+
+	if err := invalidConfig.Validate(); err != nil &&
+		(err.Error() == "" || err.Error() == "workspace is required" ||
+			err.Error() == "agents config validation failed: defaults: workspace is required") {
+		// Expected error condition
+	} else if err != nil {
+		t.Logf("Got expected error for invalid config: %v", err)
+	}
+}
+
+func TestConfigValidation_ChannelRequirements(t *testing.T) {
+	// Test telegram with enabled but no token
+	invalidTelegramConfig := &Config{
+		Agents: AgentsConfig{
+			Defaults: AgentDefaults{
+				Workspace: "~/test-workspace",
+				Model:     "test-model",
+			},
+		},
+		Channels: ChannelsConfig{
+			Telegram: TelegramConfig{
+				Enabled: true, // Enabled but no token
+				Token:   "",   // Missing required token
+			},
+		},
+		Gateway: GatewayConfig{
+			Host: "localhost",
+			Port: 8080,
+		},
+		ModelList: []ModelConfig{
+			{
+				ModelName: "test-model",
+				Model:     "openai/gpt-test",
+			},
+		},
+	}
+
+	if err := invalidTelegramConfig.Validate(); err == nil {
+		t.Error("Invalid telegram config (missing token) should produce validation error, but didn't get one")
+	} else {
+		t.Logf("Got expected error for invalid telegram config: %v", err)
+	}
+}