Add mcp_adapter_server_config filter to McpServer constructor for all servers

[raftaar1191]

Summary

There is currently no filter that allows modifying the configuration of all MCP servers at construction time. The existing mcp_adapter_default_server_config filter only covers the default server created by DefaultServerFactory.

Problem

When McpServer::__construct() is called — whether for the default server or any custom server created via mcp_adapter_init — there is no way to alter its configuration (server name, route namespace, tools, resources, prompts, etc.) without forking the creation logic.

This makes it impossible for plugins to:

• Add or remove abilities from any server's tools/resources/prompts list
• Rename or reroute a server they did not create
• Apply site-wide rules (e.g. visibility allowlists) across all servers uniformly

Proposed Solution

Add a single filter at the top of McpServer::__construct(), before parameters are assigned to properties:

/**
 * Filters the configuration of any MCP server before it is applied.
 *
 * Fires for ALL servers during construction. Use $config['server_id']
 * to target a specific server or apply changes to all servers.
 *
 * @since 0.6.0
 *
 * @param array  $config {
 *     Server configuration array.
 *
 *     @type string   $server_id              Server identifier.
 *     @type string   $server_route_namespace REST API namespace.
 *     @type string   $server_route           REST API route.
 *     @type string   $server_name            Human-readable server name.
 *     @type string   $server_description     Server description.
 *     @type string   $server_version         Server version.
 *     @type string[] $tools                  Ability names to expose as tools.
 *     @type string[] $resources              Ability names to expose as resources.
 *     @type string[] $prompts                Ability names to expose as prompts.
 * }
 * @param string $server_id The server identifier (for convenience — same as $config['server_id']).
 */
$config = apply_filters( 'mcp_adapter_server_config', $config, $server_id );

The filter fires inside __construct() after parameters are packed into a $config array and before they are unpacked into instance properties. The rest of the constructor continues unchanged.

Location

includes/Core/McpServer.php — top of __construct(), before line 144 where properties are assigned.

Use Case Example

add_filter( 'mcp_adapter_server_config', function( array $config, string $server_id ) {
    // Remove a specific ability from tools on all servers.
    $config['tools'] = array_diff( $config['tools'], array( 'core/get-environment-info' ) );

    // Rename a specific server.
    if ( 'mcp-adapter-default-server' === $server_id ) {
        $config['server_name'] = 'My Custom Server Name';
    }

    return $config;
}, 10, 2 );

Why One Filter Instead of Many

A single filter receiving the full config array is preferred over per-parameter filters (mcp_adapter_server_tools, mcp_adapter_server_name, etc.) because:

• Single hook to learn and maintain
• Tools, resources, and prompts are often modified together based on the same logic
• $server_id as the second parameter allows targeting specific or all servers
• Consistent shape with the existing mcp_adapter_default_server_config filter

Relationship to mcp_adapter_default_server_config

mcp_adapter_default_server_config fires inside DefaultServerFactory before the default server is constructed — it shapes the config before it reaches McpServer::__construct(). The proposed mcp_adapter_server_config fires inside __construct() itself, covering all servers regardless of how they were created. The two filters are complementary, not redundant.