src/legacy-era.ts

Functions

Imports

It imports no other module of this repo. Imported by src/mcp-handler.ts.

Source

1// THE PRIOR-ERA SHIM. One module, one call site in src/mcp-handler.ts, deletable as a
2// unit. The pattern is Carrel's (app/lib/mcp/legacy-era.ts), copied from
3// dustinedwards-mcp, where it was measured.
4//
5// ============================================================================
6// REMOVAL CONDITION
7// ============================================================================
8// Delete this file, its single call site in src/mcp-handler.ts, and 2025-11-25 from ERAS in
9// scripts/mcp-probe-lib.mjs (live gate 8 calls both eras) when the probe in
10// dustinedwards-mcp (`node scripts/probe-report.mjs`) shows the clients that reach
11// Capsid opening with `server/discover` instead of `initialize`. Capsid's own
12// admin_client_audit rows (src/admin-client-audit.ts) record the protocol version the
13// admin's client sends and are a second reading.
14//
15// Targets and their last measurement (in dustinedwards-mcp; Capsid has no probe of its
16// own):
17//   Claude Code 2.1.203   2026-07-29   LEGACY (initialize, 2025-11-25)
18//   claude.ai (Anthropic) 2026-07-30   LEGACY (initialize, 2025-11-25)
19//
20// Do NOT delete it on the strength of a release note or an announcement that a client
21// "supports" the new revision. Re-run the probe and delete it on the capture.
22// ============================================================================
23//
24// WHY IT EXISTS. MCP 2026-07-28 removed the `initialize` handshake, sessions and the GET
25// stream. The primary handler is built `legacy: "reject"`, stateless and modern-only. A
26// legacy client against a modern-only server fails with no fall-forward, and every
27// driver and connector measured is legacy, so this shim is load-bearing today.
28//
29// WHY IT IS SHAPED THIS WAY. `createMcpHandler` could serve both eras from one handler
30// with `legacy: "stateless"`, but then the compatibility path would live inside the
31// library behind a flag. Routing in front of a `legacy: "reject"` handler, as the
32// library documents on `isLegacyRequest`, makes the seam real: deleting this file
33// leaves a modern-only server.
34
35import { isLegacyRequest } from "@modelcontextprotocol/server";
36import { createMcpHandler, type CreateMcpHandlerOptions, type StatelessMcpHandler } from "agents/mcp/server";
37
38/** The single predicate this module exports for the routing decision. */
39export { isLegacyRequest };
40
41/**
42 * The prior-era handler: each legacy request is answered by a fresh server from the
43 * same factory, and 2025-era session operations (GET and DELETE) are answered 405, as
44 * the modern handler does.
45 */
46export function createLegacyEraHandler(
47  factory: Parameters<typeof createMcpHandler>[0],
48  options: Omit<CreateMcpHandlerOptions, "legacy">
49): StatelessMcpHandler {
50  return createMcpHandler(factory, { ...options, legacy: "stateless" });
51}