import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
let cachedTaskToolSupport: boolean | undefined;
function detectTaskToolSupport(): boolean {
if (cachedTaskToolSupport !== undefined) {
return cachedTaskToolSupport;
}
try {
// Instantiate a minimal, unconnected probe server to duck-type check for
// task tool support. The probe has no transport or active connections, so
// close() only releases in-memory state; fire-and-forget is safe here.
const probe = new McpServer(
{
name: 'filesystem-mcp-capability-probe',
version: '0.0.0',
},
{ capabilities: { tools: {} } }
);
cachedTaskToolSupport =
typeof probe.experimental.tasks.registerToolTask === 'function';
probe.close().catch(() => {});
} catch {
cachedTaskToolSupport = false;
}
return cachedTaskToolSupport;
}
interface CapabilityOptions {
enablePromptListChanged?: boolean;
enableTaskToolRequests?: boolean;
}
type ServerCapabilities = NonNullable<
ConstructorParameters<typeof McpServer>[1]
>['capabilities'];
type NonOptionalServerCapabilities = NonNullable<ServerCapabilities>;
export function buildServerCapabilities(
options: CapabilityOptions = {}
): NonOptionalServerCapabilities {
const capabilities: NonOptionalServerCapabilities = {
logging: {},
resources: {},
tools: {},
prompts: options.enablePromptListChanged ? { listChanged: true } : {},
completions: {},
};
if (options.enableTaskToolRequests) {
// NOTE: enabling task tool requests requires the caller to configure
// an InMemoryTaskStore and InMemoryTaskMessageQueue on the McpServer.
// InMemoryTaskStore accumulates completed task records with no TTL eviction —
// suitable for short-lived stdio sessions. Long-running HTTP servers should
// replace it with a TTL-evicting store to avoid unbounded memory growth.
capabilities.tasks = {
list: {},
cancel: {},
requests: { tools: { call: {} } },
};
}
return capabilities;
}
export function supportsTaskToolRequests(): boolean {
return detectTaskToolSupport();
}
