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/router/admin/usersRust.controller.js

@@ -0,0 +1,71 @@
+// ── The `admin.users.detail` slot's handlers ──────────────────────────────
+//
+// What an operator can see and do about one website user's Rust identity. The
+// user id is the PARENT's — `req.params.id` off core's `/admin/users/:id` — and
+// every statement here is scoped by it, so a panel opened on one user cannot
+// read or write another's rows by editing a path segment.
+
+const core = require('../../core')
+
+const links = require('../../model/links/links.model')
+
+const log = core.logger('admin')
+
+/**
+ * GET /admin/users/:id/rust/links
+ *
+ * The linked Steam accounts and, per server, what this module knows about the
+ * player behind them — all-time rather than this wipe's, because an operator
+ * looking at a user wants their history and the public leaderboard already
+ * answers the other question.
+ *
+ * **An empty array is an answer.** Most users have no Rust link at all, and the
+ * panel renders nothing rather than an error for them.
+ */
+async function listLinks(req, res) {
+  try {
+    res.json({ links: await links.forAdmin(req.params.id) })
+  } catch (err) {
+    log.error('failed to read a user’s Rust links', { error: err.message })
+    res.status(500).json({ error: 'Failed to read this user’s Rust accounts' })
+  }
+}
+
+/**
+ * DELETE /admin/users/:id/rust/links/:steamId — staff sever a link (D25).
+ *
+ * **This is the counterweight to D23.** The site refuses to move a Steam id that
+ * another website account already holds, and the player's own way out is
+ * `/unlink` in game — which is no way out at all for somebody who has lost access
+ * to that Steam account, or to the site account holding it. Staff are that route.
+ *
+ * Scoped by the parent user id in the statement rather than checked first: the
+ * ownership test and the deletion are one operation, and a link that belongs to a
+ * different user answers 404 from the page it was not on.
+ */
+async function removeLink(req, res) {
+  const { steamId } = req.params
+  const userId = req.params.id
+
+  try {
+    const removed = await links.unlinkOwned(steamId, userId)
+
+    if (!removed) return res.status(404).json({ error: 'That account is not linked to this user' })
+
+    // The one write this panel has, so it is the one thing here worth an audit
+    // row: after phase 7 a link is what permissions are granted against, and
+    // "who severed it" stops being a curiosity.
+    await core.activity.log({
+      req,
+      action: 'rust.account.unlink.staff',
+      detail: { steamId, userId: Number(userId) },
+    })
+
+    return res.json({ unlinked: true })
+  } catch (err) {
+    log.error('failed to unlink a Steam account', { error: err.message })
+    return res.status(500).json({ error: 'Failed to unlink that account' })
+  }
+}
+
+module.exports = { listLinks, removeLink }