feat(rust): identity — a link code from the game, and the Steam id inside core's user page

R1's identity link, site-side, and R13's first extension slot. A player types
/link in game, the plugin hands them a six-character code privately, and they
enter it here; the site records who owns which Steam account, and an operator
sees that on core's own `/admin/users/:id` page.

**The site is the author of record and the game holds nothing.** There is no
per-account store in Rust that survives a wipe, and phase 7 needs the site
authoritative anyway — it pushes permissions INTO the game keyed by Steam id. A
copy in the game would be a second thing to reconcile every wipe, for no question
it could answer better.

## D24 — a code is minted by ONE server, so every server is asked

Nothing in six characters says where it came from. The fleet is asked in turn and
the first `link.ok` wins; the others answer `unknown` and nothing happens there,
because a code is only spent at the server that actually holds it. Asking the
player to pick was rejected: a wrong pick would come back indistinguishable from
a wrong code, and that is the one refusal which must not be ambiguous.

**"Every reachable server refused" is not the same answer as "a server was
unreachable."** Collapsing them tells a player whose server is down that their
code is wrong — so they run /link again on that same server and are told the same
thing for as long as it stays down. `unsure` is that case, and it says to try
again rather than to fetch a new code.

## D23 — a Steam id another account holds is refused, never moved

The primary key is `steam_id`, and it is load-bearing rather than tidy: phase 7
grants permissions against a link and phase 13 hangs entitlements off it, so a
silent move is an account takeover performed by typing six characters. The
refusal names the holder, because the advice is unusable without it. The INSERT
is a plain INSERT for the same reason — `ON DUPLICATE KEY UPDATE` here would BE
that move — and the duplicate-key error is the refusal for the race the check
above cannot close.

The way out is `/unlink` in game, which reaches the site off the ingest feed
rather than through a route (the plugin has no link to delete). D25 adds the
other way out: staff can sever a link from the admin panel, for a player who
cannot reach that Steam account in game.

## The slot, and the hole it found in this repo's own generator

`admin.users.detail` is declared in `module.json` AND registered in `index.js`
AND filled by the chunk — three places, because the server half and the client
half are different registrations that share one name.

`swaggerFragment.js` knew only about tier routers, so the two routes under
`/admin/users/:id` were generated by nothing: a fragment that was internally
consistent and described two routes fewer than the module serves. A slot's mount
is core's and cannot be derived here, so it is a fourth constant beside
`TIER_BASE` — held to account by the frozen-manifest job, which was verified to
catch exactly this by removing the two paths and watching it fail.

## Smaller things worth knowing

- **Core's `useAsync` has no `refresh`.** A counter in the deps is how a page
  re-reads after its own write; it blanks while it re-reads, which is right here
  and is exactly what made it wrong for a poll.
- **Every player-portal nav row needs an `icon`** — core draws one on every row,
  and the client suite says so. This module had no icons file until now, because
  the public header is text buttons.
- The two new frame kinds are STAFF-only. Neither carries a code, but both name a
  Steam id beside a website account's activity, and that join is not a public
  fact about what happened on a server.
- The link code route carries its own rate limiter rather than core's
  `accountChangeLimiter`: this is guessing somebody else's secret, not changing
  your own password, and a shared counter would let one policy set the other.

Protocol 3 on all three declaration sites; 17 new tests, 136 green.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PMH6bw1jXMgbyF3ZWGEzSM

server/test/identityRoutes.test.js

@@ -0,0 +1,82 @@
+// ── The shape of the identity surface ─────────────────────────────────────
+//
+// Three properties that are invisible in review and expensive in production:
+//
+//   • **the link route is rate-limited** (R1). Six characters from a 32-glyph
+//     alphabet is a good code only while a guesser is made to pay per attempt,
+//     and once phase 7 grants permissions against a link, guessing one is a
+//     privilege-escalation path rather than a nuisance.
+//   • **the extension router merges its parent's params**. Without
+//     `mergeParams`, `req.params.id` is `undefined` and every statement in that
+//     panel silently scopes to no user — a panel that reads as "this user has no
+//     Rust account" for everybody.
+//   • **the extension's paths keep the module's own segment.** Core owns
+//     `/admin/users/:id`; a bare `/links` would be this module claiming a word on
+//     a URL it does not own, and the next module to fill a slot would collide.
+
+const test = require('node:test')
+const assert = require('node:assert')
+
+const { fakeCtx, fakeApi } = require('./_fakes')
+
+function register(ctx = fakeCtx()) {
+  require('../core')._reset()
+  const api = fakeApi()
+  require('../index')(ctx, api)
+  return api
+}
+
+/** `[{ method, path, handlers }]` for one express router. */
+function routesOf(router) {
+  return router.stack
+    .filter((layer) => layer.route)
+    .map((layer) => ({
+      path: layer.route.path,
+      method: Object.keys(layer.route.methods)[0].toUpperCase(),
+      handlers: layer.route.stack.map((s) => s.handle),
+    }))
+}
+
+test('the player tier serves the three identity routes, and nothing else new', () => {
+  const api = register()
+  const routes = routesOf(api.record.routes.player['/rust'])
+
+  assert.deepEqual(
+    routes.map((r) => `${r.method} ${r.path}`).sort(),
+    ['DELETE /links/:steamId', 'GET /links', 'GET /servers', 'POST /link'],
+  )
+})
+
+test('redeeming a code is rate-limited, and by a limiter of its own', () => {
+  const api = register()
+  const post = routesOf(api.record.routes.player['/rust']).find((r) => r.method === 'POST')
+
+  // The fake's `rateLimit` hands back a pass-through carrying the options it was
+  // given, so the policy itself is assertable — a limiter that was quietly
+  // removed, or one built with core's `accountChangeLimiter` shared counter,
+  // both fail here.
+  const limiter = post.handlers.find((h) => h.options && h.options.label === 'rust-link-code')
+
+  assert.ok(limiter, 'POST /link must carry its own rate limiter (R1)')
+  assert.equal(limiter.options.max, 10)
+  assert.equal(limiter.options.windowMs, 15 * 60 * 1000)
+
+  // First in the chain: a limiter behind the validator would let an attacker
+  // spend the cheap half of the request unbounded.
+  assert.equal(post.handlers[0], limiter)
+})
+
+test('the admin.users.detail router merges the parent’s params and keeps its own segment', () => {
+  const api = register()
+  const slot = api.record.extensions.find((e) => e.slot === 'admin.users.detail')
+
+  assert.ok(slot, 'the server half of admin.users.detail must be registered')
+  assert.equal(slot.router.mergeParams, true)
+
+  const paths = routesOf(slot.router).map((r) => `${r.method} ${r.path}`).sort()
+  assert.deepEqual(paths, ['DELETE /rust/links/:steamId', 'GET /rust/links'])
+
+  for (const route of routesOf(slot.router)) {
+    assert.ok(route.path.startsWith('/rust/'), `${route.path} must live under this module's own segment`)
+  }
+})