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/ingest.test.js

@@ -327,3 +327,35 @@ test('a board replaces presence rather than appending to it', async () => {
   assert.match(presence[0].sql, /^DELETE FROM rust_presence/)
   assert.match(presence[1].sql, /INSERT INTO rust_presence/)
 })
+
+// ── Protocol 3: the frame that changes something other than a counter ─────
+
+test('an in-game /unlink severs the site link, scoped by Steam id alone', async () => {
+  const rec = withRecorder()
+  const ingest = require('../ingest')
+
+  await ingest.apply('main', item('account.unlinked', { steamId: '7656', name: 'Wanderer', origin: 'in-game' }))
+
+  const del = rec.statements.find((st) => st.sql.trim().toUpperCase().startsWith('DELETE'))
+
+  // It arrives on the FEED rather than through a route because the plugin has no
+  // link to delete — the site is the author of record. And it is the only way out
+  // of a link on the wrong account, because the site refuses to move a Steam id
+  // another account already holds (D23).
+  assert.ok(del, 'an unlink frame must delete the link')
+  assert.ok(del.sql.includes('rust_account_links'))
+  assert.deepEqual(del.params, ['7656'])
+})
+
+test('asking for a code links nothing — the code does not travel on the wire', async () => {
+  const rec = withRecorder()
+  const ingest = require('../ingest')
+
+  await ingest.apply('main', item('account.link.requested', { steamId: '7656', name: 'Wanderer', ttlSec: 300 }))
+
+  // The frame exists so an operator can see linking being used. Nothing about it
+  // is redeemable: the code travels through the player, which is what makes
+  // typing it proof that they are the one who asked.
+  assert.equal(rec.touching('rust_account_links').length, 0)
+  assert.equal(rec.touching('rust_players').length, 1)
+})