The Abilities API supports both object-based and flattened (simple type) schemas for inputs and outputs. However, MCP requires input_schema.type to always be "object".

This means the MCP adapter needs to transform flattened schemas into object structures when converting Abilities to MCP tools.

Context

Related PR: WordPress/abilities-api#61 (review)

Current Behavior

The Abilities API allows schemas like:

'input_schema' => [
    'type' => 'string',
    'description' => 'Post type to count'
]

Required Behavior

The MCP adapter must transform these into:

{
    "type": "object",
    "properties": {
        "input": {
            "type": "string",
            "description": "Post type to count"
        }
    }
}

Implementation Notes

1. Property naming: Based on discussion with @gziolo, use "input" for input schemas and "output" for output schemas
2. When to transform: Apply transformation when type !== "object"
3. Description: Copy the description from the original schema to the wrapper property if available
4. Arrays: This should also handle type: "array" cases

Additional Considerations

• Document this transformation behavior for future adapter implementations
• Consider adding tests for various simple types (string, number, boolean, array)
• Ensure the transformation preserves all schema properties (enum, format, etc.)

Acceptance Criteria

• Adapter successfully transforms flattened input schemas to MCP-compatible object format
• Adapter successfully transforms flattened output schemas to MCP-compatible object format
• Tests cover string, number, boolean, and array types
• Documentation updated to explain the transformation
• Existing object-based schemas continue to work without modification