feat(vmcp): add support for ResourceLink content type

pkg/vmcp/client/meta_integration_test.go

@@ -69,7 +69,7 @@ func TestMetaPreservation_CallTool(t *testing.T) {
 	// Verify content is also correct
 	assert.NotNil(t, result.Content)
 	assert.Len(t, result.Content, 1)
-	assert.Equal(t, "text", result.Content[0].Type)
+	assert.Equal(t, vmcp.ContentTypeText, result.Content[0].Type)
 	assert.Equal(t, "Response from test tool", result.Content[0].Text)
 }
 
@@ -111,7 +111,7 @@ func TestMetaPreservation_CallTool_NoMeta(t *testing.T) {
 	// Verify content is still correct
 	assert.NotNil(t, result.Content)
 	assert.Len(t, result.Content, 1)
-	assert.Equal(t, "text", result.Content[0].Type)
+	assert.Equal(t, vmcp.ContentTypeText, result.Content[0].Type)
 }
 
 // TestMetaPreservation_CallTool_Error tests that _meta fields are preserved even when tool returns IsError=true.

pkg/vmcp/composer/workflow_engine_test.go

@@ -137,15 +137,15 @@ func TestWorkflowEngine_ExecuteWorkflow_IsErrorHandling(t *testing.T) {
 			Return(&vmcp.ToolCallResult{
 				IsError: true,
 				Content: []vmcp.Content{{
-					Type: "text",
+					Type: vmcp.ContentTypeText,
 					Text: "Tool execution failed: invalid input",
 				}},
 			}, nil),
 		te.Backend.EXPECT().CallTool(gomock.Any(), target, "test.tool", gomock.Any(), gomock.Any()).
 			Return(&vmcp.ToolCallResult{
 				IsError: true,
 				Content: []vmcp.Content{{
-					Type: "text",
+					Type: vmcp.ContentTypeText,
 					Text: "Tool execution failed: temporary error",
 				}},
 			}, nil),
@@ -190,7 +190,7 @@ func TestWorkflowEngine_ExecuteWorkflow_IsErrorExhaustsRetries(t *testing.T) {
 		Return(&vmcp.ToolCallResult{
 			IsError: true,
 			Content: []vmcp.Content{{
-				Type: "text",
+				Type: vmcp.ContentTypeText,
 				Text: "Persistent error: operation failed",
 			}},
 		}, nil).Times(3) // Initial + 2 retries

pkg/vmcp/conversion/content.go

@@ -17,34 +17,36 @@ import (
 	"github.com/stacklok/toolhive/pkg/vmcp"
 )
 
-const (
-	contentTypeText     = "text"
-	contentTypeImage    = "image"
-	contentTypeAudio    = "audio"
-	contentTypeResource = "resource"
-)
-
 // ConvertMCPContent converts a single mcp.Content item to vmcp.Content.
 // Unknown content types are returned as vmcp.Content{Type: "unknown"}.
 func ConvertMCPContent(content mcp.Content) vmcp.Content {
 	if text, ok := mcp.AsTextContent(content); ok {
-		return vmcp.Content{Type: contentTypeText, Text: text.Text}
+		return vmcp.Content{Type: vmcp.ContentTypeText, Text: text.Text}
 	}
 	if img, ok := mcp.AsImageContent(content); ok {
-		return vmcp.Content{Type: contentTypeImage, Data: img.Data, MimeType: img.MIMEType}
+		return vmcp.Content{Type: vmcp.ContentTypeImage, Data: img.Data, MimeType: img.MIMEType}
 	}
 	if audio, ok := mcp.AsAudioContent(content); ok {
-		return vmcp.Content{Type: contentTypeAudio, Data: audio.Data, MimeType: audio.MIMEType}
+		return vmcp.Content{Type: vmcp.ContentTypeAudio, Data: audio.Data, MimeType: audio.MIMEType}
 	}
 	if res, ok := mcp.AsEmbeddedResource(content); ok {
 		if textRes, ok := mcp.AsTextResourceContents(res.Resource); ok {
-			return vmcp.Content{Type: "resource", Text: textRes.Text, URI: textRes.URI, MimeType: textRes.MIMEType}
+			return vmcp.Content{Type: vmcp.ContentTypeResource, Text: textRes.Text, URI: textRes.URI, MimeType: textRes.MIMEType}
 		}
 		if blobRes, ok := mcp.AsBlobResourceContents(res.Resource); ok {
-			return vmcp.Content{Type: "resource", Data: blobRes.Blob, URI: blobRes.URI, MimeType: blobRes.MIMEType}
+			return vmcp.Content{Type: vmcp.ContentTypeResource, Data: blobRes.Blob, URI: blobRes.URI, MimeType: blobRes.MIMEType}
 		}
 		slog.Debug("Embedded resource has unknown resource contents type", "type", fmt.Sprintf("%T", res.Resource))
-		return vmcp.Content{Type: "resource"}
+		return vmcp.Content{Type: vmcp.ContentTypeResource}
+	}
+	if link, ok := content.(mcp.ResourceLink); ok {
+		return vmcp.Content{
+			Type:        vmcp.ContentTypeLink,
+			URI:         link.URI,
+			Name:        link.Name,
+			Description: link.Description,
+			MimeType:    link.MIMEType,
+		}
 	}
 	slog.Debug("Encountered unknown MCP content type", "type", fmt.Sprintf("%T", content))
 	return vmcp.Content{Type: "unknown"}
@@ -64,13 +66,13 @@ func ConvertMCPContents(contents []mcp.Content) []vmcp.Content {
 // Unknown content types are converted to empty text with a warning.
 func ToMCPContent(content vmcp.Content) mcp.Content {
 	switch content.Type {
-	case contentTypeText:
+	case vmcp.ContentTypeText:
 		return mcp.NewTextContent(content.Text)
-	case contentTypeImage:
+	case vmcp.ContentTypeImage:
 		return mcp.NewImageContent(content.Data, content.MimeType)
-	case contentTypeAudio:
+	case vmcp.ContentTypeAudio:
 		return mcp.NewAudioContent(content.Data, content.MimeType)
-	case contentTypeResource:
+	case vmcp.ContentTypeResource:
 		// Reconstruct embedded resource from vmcp.Content fields.
 		// Text content takes precedence over blob content when both are present.
 		if content.Text != "" {
@@ -94,6 +96,9 @@ func ToMCPContent(content vmcp.Content) mcp.Content {
 			MIMEType: content.MimeType,
 			Text:     "",
 		})
+	case vmcp.ContentTypeLink:
+		// Reconstruct a ResourceLink from vmcp.Content fields.
+		return mcp.NewResourceLink(content.URI, content.Name, content.Description, content.MimeType)
 	default:
 		slog.Warn("converting unknown content type to empty text - this may cause data loss", "type", content.Type)
 		return mcp.NewTextContent("")
@@ -264,23 +269,25 @@ func ContentArrayToMap(content []vmcp.Content) map[string]any {
 
 	for _, item := range content {
 		switch item.Type {
-		case contentTypeText:
-			key := contentTypeText
+		case vmcp.ContentTypeText:
+			key := string(vmcp.ContentTypeText)
 			if textIndex > 0 {
 				key = fmt.Sprintf("text_%d", textIndex)
 			}
 			result[key] = item.Text
 			textIndex++
 
-		case contentTypeImage:
+		case vmcp.ContentTypeImage:
 			key := fmt.Sprintf("image_%d", imageIndex)
 			result[key] = item.Data
 			imageIndex++
 
-			// Default case (implicit):
+		case vmcp.ContentTypeAudio, vmcp.ContentTypeResource, vmcp.ContentTypeLink:
+			// Purposely ignored for template substitution:
 			// - Audio content is ignored (not supported for template substitution)
-			// - Resource content is ignored (handled separately, not converted to map)
-			// - Unknown content types are ignored (warnings logged at conversion boundaries)
+			// - Resource content/link is handled separately, not converted to map
+		default:
+			// Unknown content types are ignored (warnings logged at conversion boundaries)
 		}
 	}