feat(rust): site-owned permissions — the site is the author, the game is the cache

R2, and the first phase where this module WRITES to a game. Groups and grants are
authored on the website and pushed into each server's own permission store, so
every plugin that already calls `UserHasPermission` honours them with no adapter,
and a wipe stops being a data-loss event.

**Seven org-lead decisions (D28-D34).** A grant is keyed to the website USER and
resolved to every Steam id they have linked at push time (D28); every authored row
carries a scope — a server or `*` (D29); groups are mirrored as real groups rather
than flattened (D30); a holder the site did not author is REPORTED, never undone,
with adopt and revoke offered (D31); one verb, with the plugin diffing locally
(D32); a permission no server has registered is reported unresolved and never
self-registered (D33); authoring is people and groups by hand, with rules deferred
(D34).

**Three sets, and every interesting question is a difference between two.**
`desired − pushed` is what to apply; `pushed − desired` is what to RETIRE, because
the site put it there and has since withdrawn it; `present − desired` is drift. The
middle one is why `rust_perm_pushed` exists: a name in the store that is not in the
desired set is either something the site retired or something a human granted, and
those two have opposite correct answers.

**What lands is not what was sent.** A grant naming a permission the server has not
registered did not land — `GrantUserPermission` no-ops silently — and a member the
store has never seen could not be placed. Neither is recorded as pushed, so the
site never believes it gave a privilege it did not.

The loop asks a cheap question every thirty seconds — does the digest of the
desired set still equal what this server last confirmed — and syncs on a change, a
restart, a wipe, a drift hook, a failed attempt past its backoff, or the
fifteen-minute audit that finds drift on a server nobody has touched.

**This module's first admin page**, because a permission model is the first thing
here that has to be composed rather than configured. What is on it is decided by
what an operator can get wrong: four states are invisible from the game and from a
list of grants, and each is a sentence rather than a number.

Walked end to end against a real core at the pinned ref, the real sidecar, and a
stand-in speaking protocol 4 — including a restart that emptied the store and was
fully re-pushed. Four defects the browser found that 133 green tests did not.

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

client/src/api.js

@@ -103,6 +103,50 @@ export const admin = {
     req(`/admin/rust/servers/${encodeURIComponent(id)}/test`, { method: 'POST' }),
 }
 
+// ── admin · permissions (R2) ──────────────────────────────────────────────
+//
+// The authoring surface. Every call here writes to the SITE, and none of them
+// reaches a game server — the mirror's own loop does that on its own cadence.
+// `sync` is the exception and says so in its name: it runs the pass now and
+// answers with what each server reported, which is the only call on this screen
+// that can be slow or fail because a game host is down.
+//
+// A write is followed by a re-read rather than a local edit of the model: what
+// the screen is showing is partly the game's answer, and the honest way to learn
+// the new one is to ask.
+export const adminPermissions = {
+  overview: () => req('/admin/rust/permissions'),
+  catalogue: () => req('/admin/rust/permissions/catalogue'),
+
+  saveGroup: (name, body) =>
+    req(`/admin/rust/permissions/groups/${encodeURIComponent(name)}`, { method: 'PUT', body }),
+  deleteGroup: (name) =>
+    req(`/admin/rust/permissions/groups/${encodeURIComponent(name)}`, { method: 'DELETE' }),
+
+  addMember: (name, username) =>
+    req(`/admin/rust/permissions/groups/${encodeURIComponent(name)}/members`, {
+      method: 'POST',
+      body: { username },
+    }),
+  removeMember: (name, userId) =>
+    req(
+      `/admin/rust/permissions/groups/${encodeURIComponent(name)}/members/${encodeURIComponent(userId)}`,
+      { method: 'DELETE' },
+    ),
+
+  grant: (body) => req('/admin/rust/permissions/grants', { method: 'POST', body }),
+  revoke: (id) =>
+    req(`/admin/rust/permissions/grants/${encodeURIComponent(id)}`, { method: 'DELETE' }),
+
+  adoptDrift: (id) =>
+    req(`/admin/rust/permissions/drift/${encodeURIComponent(id)}/adopt`, { method: 'POST' }),
+  revokeDrift: (id) =>
+    req(`/admin/rust/permissions/drift/${encodeURIComponent(id)}/revoke`, { method: 'POST' }),
+
+  sync: (serverId = null) =>
+    req('/admin/rust/permissions/sync', { method: 'POST', body: serverId ? { serverId } : {} }),
+}
+
 // ── the admin.users.detail extension slot ─────────────────────────────────
 //
 // The client half of R13's first slot. Core hands the component a `userId` and
@@ -118,8 +162,34 @@ export const adminUserLinks = {
     }),
 }
 
+// The same panel's phase 7 half: what this person may do in game. The id in the
+// path is the one the slot handed the component, so these send `userId` rather
+// than a name — the screen already knows who it is looking at.
+export const adminUserPermissions = {
+  list: (userId) => req(`/admin/users/${encodeURIComponent(userId)}/rust/permissions`),
+  grant: (userId, body) =>
+    req(`/admin/users/${encodeURIComponent(userId)}/rust/permissions/grants`, {
+      method: 'POST',
+      body,
+    }),
+  revoke: (userId, grantId) =>
+    req(
+      `/admin/users/${encodeURIComponent(userId)}/rust/permissions/grants/${encodeURIComponent(grantId)}`,
+      { method: 'DELETE' },
+    ),
+}
+
 // Exported for the rare caller that needs the base itself — an `<img src>`, a
 // download link, an EventSource. Reach for `request` first.
 export { BASE, query }
 
-export default { servers, playerServers, playerLinks, admin, adminUserLinks, BASE }
+export default {
+  servers,
+  playerServers,
+  playerLinks,
+  admin,
+  adminPermissions,
+  adminUserLinks,
+  adminUserPermissions,
+  BASE,
+}