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/scripts/swaggerFragment.js

@@ -60,6 +60,22 @@ const TIER_BASE = {
   player: '/api/v1/player',
 }
 
+// MODULE_API.md §2.4's slot table, and the FOURTH base this generator needs.
+//
+// Phase 6 found the hole: a slot router is not registered under a tier, so the
+// loop below could not see it and the two routes it serves were generated by
+// nothing — a fragment that was internally consistent and silently described two
+// routes fewer than the module serves. The frozen-manifest check would have
+// caught it (every route must have an operation), which is precisely why that
+// check exists; this is the fix it points at.
+//
+// A slot's mount is CORE's, not ours, so it cannot be derived from anything in
+// this repo. That makes it the same kind of constant as `TIER_BASE` above, and it
+// is held to account the same way: by a real core in the frozen-manifest job.
+const SLOT_MOUNT = {
+  'admin.users.detail': '/api/v1/admin/users/:id',
+}
+
 /**
  * Run `register()` with a recording api and return `[{ file, prefix, what }]`.
  *
@@ -88,6 +104,15 @@ function mountedRouters() {
     }
   }
 
+  // A filled slot is a mount too. Registered through a different call, mounted
+  // on a resource core owns, and — unlike a tier router — carrying the parent's
+  // `:id` in its own base path.
+  for (const { slot, router } of api.record.extensions || []) {
+    const mount = SLOT_MOUNT[slot]
+    if (!mount) throw new Error(`swagger: filled slot "${slot}", which §2.4's table does not list`)
+    mounts.push({ router, prefix: mount, what: `slot ${slot}` })
+  }
+
   return mounts.map(({ router, prefix, what }) => {
     const file = fileOf(router)
     if (!file) {