Understudy

Real MCP rehearsal: changing the requested kit exposes an unset substitution rule. Fictional demo records.

An equipment desk can have a handbook and still lack an answer to a routine request. A borrower asks for a camera that is already on loan. Another camera is available, but nobody has decided whether the desk can offer a substitute.

Understudy makes that missing decision visible. An operator records equipment, borrowers and explicit lending rules, then rehearses a request. The MCP tools inspect the desk and change one fact at a time: borrower verification, eligibility, maintenance or the equipment originally requested. Each comparison shows the changed fact, resulting answer and rules checked.

The operator can distinguish missing evidence from a missing instruction. Verifying a borrower requires evidence. Choosing whether substitutes are allowed requires a policy decision. After the operator adds a confirmation rule, the rehearsal permits a confirmed substitute and asks for consent when confirmation is absent.

The private workspace also supports inventory imports, loans, renewals, component returns and durable receipts. Concurrent requests cannot check out the same item twice, and retrying a committed request returns its existing receipt. The judge demonstration uses isolated fictional records without account access or private data.

Alexa+ track demonstration

This entry uses the event's permitted self-hosted MCP route: the official TypeScript MCP SDK, protocol 2025-11-25 and Streamable HTTP. A browser client demonstrates real calls to inspect_desk and probe_request. The private endpoint also exposes read_receipt. The fictional demo cannot access committed receipts or lend equipment.

The evaluator applies explicit configured rules. It does not interpret handbook prose with an LLM. Alexa+ distribution, Echo-device interaction and AWS services are not connected.

Run and verify

Use Node 22.13 or later. Clone the GitHub repository, run npm ci, then npm run dev -- --hostname 127.0.0.1 --port 4320. Open http://localhost:4320/demo. No cloud account, credentials or database setup is needed for this demonstration. docs/JUDGING.md contains the walkthrough; README.md covers local D1 setup for the full operator workspace.

A fresh installation passed all 35 domain, SQLite, MCP and demo tests, TypeScript checks, lint and a production build. HTTP checks against the clean copy verified MCP negotiation, consent boundaries, private-data isolation and the full D1-backed lending lifecycle.

Development and design

Built with Codex using React, TypeScript, Vinext, Cloudflare D1, Drizzle and the MCP SDK. The interface uses grouped navigation and progressive detail inspired by 21st.dev, with original implementation in the existing typography and colors. Tool feedback and observed friction are included in the repository.