Fix metadata loss in AgentCard legacy capability unmarshaling

internal/a2a/models/agent_card.go

@@ -105,16 +105,14 @@ func (a *AgentCard) UnmarshalJSON(data []byte) error {
 
 	// Check if capabilities is present and try legacy formats first
 	var hasLegacyCap bool
+	var legacyCapabilities []Capability
 	if capRaw, exists := raw["capabilities"]; exists {
 		// Try legacy array format []Capability
 		var legacyCaps []Capability
 		if err := json.Unmarshal(capRaw, &legacyCaps); err == nil && len(legacyCaps) > 0 {
 			// Convert legacy array to new Capabilities object structure
-			// Store in metadata for backward compatibility
-			if a.Metadata == nil {
-				a.Metadata = make(map[string]any)
-			}
-			a.Metadata["legacyCapabilities"] = legacyCaps
+			// Store in a temporary variable to preserve across struct assignment
+			legacyCapabilities = legacyCaps
 			hasLegacyCap = true
 		} else if err == nil {
 			// Empty array, still legacy format
@@ -147,10 +145,8 @@ func (a *AgentCard) UnmarshalJSON(data []byte) error {
 							Description: description,
 						})
 					}
-					if a.Metadata == nil {
-						a.Metadata = make(map[string]any)
-					}
-					a.Metadata["legacyCapabilities"] = legacyCaps
+					// Store in a temporary variable to preserve across struct assignment
+					legacyCapabilities = legacyCaps
 					hasLegacyCap = true
 				}
 			} else {
@@ -177,6 +173,14 @@ func (a *AgentCard) UnmarshalJSON(data []byte) error {
 			return err
 		}
 		*a = AgentCard(*aux)
+
+		// Restore legacy capabilities after struct assignment
+		if len(legacyCapabilities) > 0 {
+			if a.Metadata == nil {
+				a.Metadata = make(map[string]any)
+			}
+			a.Metadata["legacyCapabilities"] = legacyCapabilities
+		}
 	} else {
 		// New schema format, unmarshal normally
 		aux := &Alias{}

tests/a2a/agent_card_metadata_preservation_test.go

@@ -0,0 +1,121 @@
+package a2a
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/techbuzzz/agent-shaker/internal/a2a/models"
+)
+
+func TestAgentCardUnmarshal_MetadataPreservation(t *testing.T) {
+	// Test that legacy capabilities are preserved in metadata after struct assignment
+	jsonData := `{
+		"name": "Test Agent",
+		"version": "1.0.0",
+		"capabilities": [
+			{
+				"type": "task",
+				"description": "Task execution"
+			},
+			{
+				"type": "streaming",
+				"description": "SSE streaming"
+			}
+		],
+		"endpoints": [],
+		"metadata": {
+			"existingKey": "existingValue"
+		}
+	}`
+
+	var card models.AgentCard
+	err := json.Unmarshal([]byte(jsonData), &card)
+	if err != nil {
+		t.Fatalf("Failed to unmarshal: %v", err)
+	}
+
+	// Check if metadata exists
+	if card.Metadata == nil {
+		t.Fatal("Metadata is nil")
+	}
+
+	// Check if legacy capabilities are preserved
+	legacyCaps, ok := card.Metadata["legacyCapabilities"]
+	if !ok {
+		t.Fatal("legacyCapabilities not found in metadata - the fix failed!")
+	}
+
+	caps, ok := legacyCaps.([]models.Capability)
+	if !ok {
+		t.Fatalf("legacyCapabilities is not []Capability, got: %T", legacyCaps)
+	}
+
+	if len(caps) != 2 {
+		t.Fatalf("Expected 2 legacy capabilities, got %d", len(caps))
+	}
+
+	if caps[0].Type != "task" || caps[0].Description != "Task execution" {
+		t.Errorf("First capability incorrect: %+v", caps[0])
+	}
+
+	if caps[1].Type != "streaming" || caps[1].Description != "SSE streaming" {
+		t.Errorf("Second capability incorrect: %+v", caps[1])
+	}
+
+	// Check if existing metadata is also preserved
+	if existingVal, ok := card.Metadata["existingKey"].(string); !ok || existingVal != "existingValue" {
+		t.Errorf("Existing metadata not preserved correctly: %v", card.Metadata["existingKey"])
+	}
+
+	t.Log("✓ Legacy capabilities correctly preserved in metadata after struct assignment")
+}
+
+func TestAgentCardUnmarshal_ObjectFormat_MetadataPreservation(t *testing.T) {
+	// Test that legacy object format capabilities are also preserved
+	jsonData := `{
+		"name": "Test Agent",
+		"version": "1.0.0",
+		"capabilities": {
+			"task": "Task execution",
+			"streaming": "SSE streaming",
+			"artifacts": "Artifact sharing"
+		},
+		"endpoints": [],
+		"metadata": {
+			"customField": "customValue"
+		}
+	}`
+
+	var card models.AgentCard
+	err := json.Unmarshal([]byte(jsonData), &card)
+	if err != nil {
+		t.Fatalf("Failed to unmarshal: %v", err)
+	}
+
+	// Check if metadata exists
+	if card.Metadata == nil {
+		t.Fatal("Metadata is nil")
+	}
+
+	// Check if legacy capabilities are preserved
+	legacyCaps, ok := card.Metadata["legacyCapabilities"]
+	if !ok {
+		t.Fatal("legacyCapabilities not found in metadata - the fix failed!")
+	}
+
+	caps, ok := legacyCaps.([]models.Capability)
+	if !ok {
+		t.Fatalf("legacyCapabilities is not []Capability, got: %T", legacyCaps)
+	}
+
+	if len(caps) != 3 {
+		t.Fatalf("Expected 3 legacy capabilities, got %d", len(caps))
+	}
+
+	// Check if existing metadata is also preserved
+	if customVal, ok := card.Metadata["customField"].(string); !ok || customVal != "customValue" {
+		t.Errorf("Existing metadata not preserved correctly: %v", card.Metadata["customField"])
+	}
+
+	t.Log("✓ Legacy object format capabilities correctly preserved in metadata")
+}