vMCP: Composite Tools supports non-string Arguments

[jerm-dro]

Summary

Fixes #2921

This PR updates the VirtualMCPServer CRD's WorkflowStep.Arguments field to support non-string value types (integers, booleans, arrays, objects). Previously, the field was defined as map[string]string, which prevented passing typed values to backend MCP tools even though the internal vmcp runtime expects map[string]any.

Problem

When defining composite tools in a VirtualMCPServer, users could not specify non-string arguments:

steps:
  - id: search
    tool: backend.search
    arguments:
      query: "{{ .params.query }}"
      max_results: 10        # ❌ This was converted to string "10"
      include_metadata: true # ❌ This was converted to string "true"

The type mismatch between the CRD (map[string]string) and the runtime (map[string]any) caused numeric and boolean values to be incorrectly converted to strings.

Solution

Changed WorkflowStep.Arguments from map[string]string to *runtime.RawExtension, which is the Kubernetes-native way to store arbitrary JSON in CRDs. This preserves the original types through the entire pipeline.

Changes

CRD Type Definition (cmd/thv-operator/api/v1alpha1/virtualmcpserver_types.go):

// Before
Arguments map[string]string `json:"arguments,omitempty"`

// After
// +kubebuilder:pruning:PreserveUnknownFields
// +kubebuilder:validation:Type=object
Arguments *runtime.RawExtension `json:"arguments,omitempty"`

Converter (cmd/thv-operator/pkg/vmcpconfig/converter.go):

• Updated convertArguments to unmarshal RawExtension into map[string]any
• Added proper error handling for invalid JSON

Webhook Validation:

• Updated template validation to handle the new argument type (virtualmcpcompositetooldefinition_webhook.go)
• Add composite tool validation to virtualmcpserver_webhook.go by factoring out a reusable function from the step above.

Tests:

• Added TestConvertCompositeTools_NonStringArguments unit test for the converter
• Added TestVMCPServer_CompositeToolNonStringArguments integration test
• Updated existing tests to use the new type

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.01%. Comparing base (71de38f) to head (ebd3951).

Files with missing lines	Patch %	Lines
...lpha1/virtualmcpcompositetooldefinition_webhook.go	69.23%	3 Missing and 1 partial ⚠️
cmd/thv-operator/pkg/vmcpconfig/converter.go	87.09%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2971      +/-   ##
==========================================
+ Coverage   56.00%   56.01%   +0.01%     
==========================================
  Files         328      328              
  Lines       32314    32337      +23     
==========================================
+ Hits        18096    18115      +19     
- Misses      12673    12675       +2     
- Partials     1545     1547       +2     

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[Copilot]

Pull request overview

This PR updates the VirtualMCPServer and VirtualMCPCompositeToolDefinition CRDs to support non-string argument types in composite tool workflow steps. Previously, the WorkflowStep.Arguments field was defined as map[string]string, which forced all argument values to be strings even when the backend MCP tools expected typed values (integers, booleans, arrays, objects). The PR changes the field type to *runtime.RawExtension, the Kubernetes-native way to preserve arbitrary JSON types in CRDs.

Key Changes:

• Changed WorkflowStep.Arguments from map[string]string to *runtime.RawExtension to preserve value types
• Updated converter logic to unmarshal RawExtension into map[string]any with proper error handling
• Updated webhook validation in VirtualMCPCompositeToolDefinition to validate Arguments JSON and template syntax
• Added comprehensive unit and integration tests for non-string argument types

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
cmd/thv-operator/api/v1alpha1/virtualmcpserver_types.go	Updated WorkflowStep.Arguments field type to *runtime.RawExtension with kubebuilder markers
cmd/thv-operator/api/v1alpha1/zz_generated.deepcopy.go	Auto-generated deepcopy method updated to handle RawExtension
cmd/thv-operator/api/v1alpha1/virtualmcpcompositetooldefinition_webhook.go	Updated template validation to unmarshal Arguments JSON and validate string values
cmd/thv-operator/api/v1alpha1/virtualmcpcompositetooldefinition_webhook_test.go	Updated tests to use RawExtension for Arguments
cmd/thv-operator/pkg/vmcpconfig/converter.go	Updated convertArguments to unmarshal RawExtension to map[string]any with error handling
cmd/thv-operator/pkg/vmcpconfig/converter_test.go	Added comprehensive tests for non-string arguments including error cases
cmd/thv-operator/controllers/virtualmcpserver_vmcpconfig_test.go	Updated controller test to use RawExtension for Arguments
test/integration/vmcp/vmcp_integration_test.go	Added integration test verifying non-string arguments flow through to backend tools
test/e2e/thv-operator/virtualmcp/virtualmcp_composite_sequential_test.go	Updated E2E test to marshal Arguments as JSON for RawExtension
test/e2e/thv-operator/virtualmcp/virtualmcp_composite_parallel_test.go	Updated E2E test to marshal Arguments as JSON for RawExtension
deploy/charts/operator-crds/crds/toolhive.stacklok.dev_virtualmcpservers.yaml	Updated CRD schema to use object type with preserve-unknown-fields
deploy/charts/operator-crds/crds/toolhive.stacklok.dev_virtualmcpcompositetooldefinitions.yaml	Updated CRD schema to use object type with preserve-unknown-fields
deploy/charts/operator-crds/Chart.yaml	Bumped chart version to 0.0.78
deploy/charts/operator-crds/README.md	Updated version badge to 0.0.78
docs/operator/crd-api.md	Updated API documentation to describe RawExtension type and template support

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