Fix MessagingConfig code review issues (gt-mrqiz, gt-ngoe6, gt-akc4m)

- Add Type field for schema consistency (gt-mrqiz)
- Fix error message inconsistency: all validation errors now wrap sentinel (gt-ngoe6)
- Add missing tests: wrong type, future version, malformed JSON (gt-akc4m)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/config/loader.go

@@ -612,6 +612,9 @@ func SaveMessagingConfig(path string, config *MessagingConfig) error {
 
 // validateMessagingConfig validates a MessagingConfig.
 func validateMessagingConfig(c *MessagingConfig) error {
+	if c.Type != "messaging" && c.Type != "" {
+		return fmt.Errorf("%w: expected type 'messaging', got '%s'", ErrInvalidType, c.Type)
+	}
 	if c.Version > CurrentMessagingVersion {
 		return fmt.Errorf("%w: got %d, max supported %d", ErrInvalidVersion, c.Version, CurrentMessagingVersion)
 	}
@@ -637,20 +640,20 @@ func validateMessagingConfig(c *MessagingConfig) error {
 	// Validate queues have at least one worker
 	for name, queue := range c.Queues {
 		if len(queue.Workers) == 0 {
-			return fmt.Errorf("%w: queue '%s' has no workers", ErrMissingField, name)
+			return fmt.Errorf("%w: queue '%s' workers", ErrMissingField, name)
 		}
 		if queue.MaxClaims < 0 {
-			return fmt.Errorf("queue '%s': max_claims must be non-negative", name)
+			return fmt.Errorf("%w: queue '%s' max_claims must be non-negative", ErrMissingField, name)
 		}
 	}
 
 	// Validate announces have at least one reader
 	for name, announce := range c.Announces {
 		if len(announce.Readers) == 0 {
-			return fmt.Errorf("%w: announce '%s' has no readers", ErrMissingField, name)
+			return fmt.Errorf("%w: announce '%s' readers", ErrMissingField, name)
 		}
 		if announce.RetainCount < 0 {
-			return fmt.Errorf("announce '%s': retain_count must be non-negative", name)
+			return fmt.Errorf("%w: announce '%s' retain_count must be non-negative", ErrMissingField, name)
 		}
 	}
 

internal/config/loader_test.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"os"
 	"path/filepath"
 	"testing"
 	"time"
@@ -575,6 +576,9 @@ func TestMessagingConfigRoundTrip(t *testing.T) {
 		t.Fatalf("LoadMessagingConfig: %v", err)
 	}
 
+	if loaded.Type != "messaging" {
+		t.Errorf("Type = %q, want 'messaging'", loaded.Type)
+	}
 	if loaded.Version != CurrentMessagingVersion {
 		t.Errorf("Version = %d, want %d", loaded.Version, CurrentMessagingVersion)
 	}
@@ -618,6 +622,7 @@ func TestMessagingConfigValidation(t *testing.T) {
 		{
 			name: "valid config with lists",
 			config: &MessagingConfig{
+				Type:    "messaging",
 				Version: 1,
 				Lists: map[string][]string{
 					"oncall": {"mayor/", "gastown/witness"},
@@ -625,6 +630,22 @@ func TestMessagingConfigValidation(t *testing.T) {
 			},
 			wantErr: false,
 		},
+		{
+			name: "wrong type",
+			config: &MessagingConfig{
+				Type:    "wrong",
+				Version: 1,
+			},
+			wantErr: true,
+		},
+		{
+			name: "future version rejected",
+			config: &MessagingConfig{
+				Type:    "messaging",
+				Version: 999,
+			},
+			wantErr: true,
+		},
 		{
 			name: "list with no recipients",
 			config: &MessagingConfig{
@@ -694,6 +715,21 @@ func TestLoadMessagingConfigNotFound(t *testing.T) {
 	}
 }
 
+func TestLoadMessagingConfigMalformedJSON(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "messaging.json")
+
+	// Write malformed JSON
+	if err := os.WriteFile(path, []byte("{not valid json"), 0644); err != nil {
+		t.Fatalf("writing test file: %v", err)
+	}
+
+	_, err := LoadMessagingConfig(path)
+	if err == nil {
+		t.Fatal("expected error for malformed JSON")
+	}
+}
+
 func TestLoadOrCreateMessagingConfig(t *testing.T) {
 	// Test creating default when not found
 	config, err := LoadOrCreateMessagingConfig("/nonexistent/path.json")

internal/config/types.go

@@ -258,7 +258,8 @@ func DefaultAccountsConfigDir() string {
 // MessagingConfig represents the messaging configuration (config/messaging.json).
 // This defines mailing lists, work queues, and announcement channels.
 type MessagingConfig struct {
-	Version int `json:"version"` // schema version
+	Type    string `json:"type"`    // "messaging"
+	Version int    `json:"version"` // schema version
 
 	// Lists are static mailing lists. Messages are fanned out to all recipients.
 	// Each recipient gets their own copy of the message.
@@ -302,6 +303,7 @@ const CurrentMessagingVersion = 1
 // NewMessagingConfig creates a new MessagingConfig with defaults.
 func NewMessagingConfig() *MessagingConfig {
 	return &MessagingConfig{
+		Type:      "messaging",
 		Version:   CurrentMessagingVersion,
 		Lists:     make(map[string][]string),
 		Queues:    make(map[string]QueueConfig),