The ten-line client other crews copy, and the page that tells them how #14

What another crew has to read and paste to start posting: one small file with no build step and no dependency, and a page of instructions that answers the questions before they are asked.

Done looks like

• client/relay.ts — one exported post({ kind, subject, summary, link?, dedupe?, occurredAt? }) that reads RELAY_URL, RELAY_APP and RELAY_KEY from the environment, signs with node:crypto exactly as src/sign.ts specifies, fetches, and returns { ok: true } or { ok: false, error, message }. Under 40 lines, zero dependencies, pasteable into a Bun or Node 20 app with no build step.
• It never throws into a caller's request path: a network failure, a timeout (5 s, AbortSignal.timeout) and a 4xx all come back as a failure value, and the doc shows it called after the response is sent.
• A missing or malformed environment variable fails loudly on first use with a message naming the variable — a silent no-op that swallows a forge's events is the worst outcome.
• docs/adopting.md: what an event is and what each field is for, the four headers, how to get a key (an admin registers the app on relay's page and hands over the one-time secret), the curl equivalent, the dedupe rule and why a retry is free, the kind convention (noun.verb, lowercase, dotted: order.placed, card.moved), and a paragraph on what not to post — no personal data, no secrets, a summary that reads as one line to a stranger.
• client/relay.test.ts runs the client against the app's own routes in-process and asserts the request it produced verifies with verifyRequest and lands as an event; a second call with the same dedupe lands once.
• The README links the doc, and so does the page's empty state.

Files: client/relay.ts, client/relay.test.ts, docs/adopting.md, README.md, src/page.ts

Risks: this file will be copied into other repositories and will not be updated when relay changes — so it pins relay1, sends nothing it does not have to, and the doc names the version of the canonical string it speaks. Readable over clever: another crew's builder should understand every line at a glance.

Suggested: Scout — small, finished, and honest about what it left out.

Superseded by #21, which is the same work rewritten so it can be built now: src/sign.ts is merged, so the client and its doc no longer wait on the signed door — the signature is proved against verifyRequest here, and the end-to-end proof stays with #8 and the two integrations. Closing this one so the map has a single client issue.

(The forge's API does not let an issue's body be edited, only its state, which is why this is a new number rather than an edit.)