diff --git a/client/src/entry.jsx b/client/src/entry.jsx
index 90209b3..3a9b142 100644
--- a/client/src/entry.jsx
+++ b/client/src/entry.jsx
@@ -189,10 +189,13 @@ registry.registerExtension(ID, 'player.invite.accepted', InviteGameAccountStep)
 // populates, but core does not own the word "guild" and publishes no Team page of
 // its own — so the page is ours and core contributes the activity feed to it.
 //
-// Declared under this module's own namespace, which core enforces. Core's fill is
-// applied after every module chunk has evaluated, so declaring it here is early
-// enough; on a core that knows nothing of Teams it simply stays empty.
-registry.declareModuleSlot(ID, 'uo.guild.detail')
+// Declared under this module's own namespace, which core enforces. The second
+// argument is what gets core's content into the place: **core offers a
+// CONTRIBUTION and never names a slot**, so this module says where each one goes
+// and keeps its own word for the place. Core's fills are applied after every
+// module chunk has evaluated, so declaring here is early enough; on a core that
+// knows nothing of Teams the slot simply stays empty.
+registry.declareModuleSlot(ID, 'uo.guild.detail', { core: 'team.activity' })
 
 // A SECOND place on the same page, for core's Team forum (TEAMS.md Part 5). Two
 // declarations rather than one, because a slot holds one component and this module
@@ -200,14 +203,14 @@ registry.declareModuleSlot(ID, 'uo.guild.detail')
 // the feed reads as part of the guild's story, the forum is a room you go into.
 // Neither knows the other exists, and a core that fills only one leaves the other
 // empty.
-registry.declareModuleSlot(ID, 'uo.guild.forum')
+registry.declareModuleSlot(ID, 'uo.guild.forum', { core: 'team.forum' })
 
 // And a THIRD, at the top of the same page, for core's per-Team notification
 // control (TEAMS.md §6.3). Same reasoning as the other two and a different place:
 // muting a guild is an action ON this page, so it sits with the page's heading
 // rather than after its content. Core resolves whether this viewer is in the
 // Team at all — this module neither knows nor asks.
-registry.declareModuleSlot(ID, 'uo.guild.header')
+registry.declareModuleSlot(ID, 'uo.guild.header', { core: 'team.notify' })
 
 // `module.json`'s `coreApi` range is checked by the loader before this file is
 // ever served, so there is nothing to re-check here. It is logged because a
diff --git a/client/test/registration.test.js b/client/test/registration.test.js
index 9e41927..8a57733 100644
--- a/client/test/registration.test.js
+++ b/client/test/registration.test.js
@@ -39,12 +39,18 @@ const CHUNK = path.resolve(HERE, '..', 'dist', 'entry.js')
 // nothing here renders, so a named stub is enough to be imported and passed on.
 const stub = (name) => Object.assign(() => null, { displayName: name })
 
+// Core's contribution catalogue, as of MODULE_API 1.6.0. Written down rather than
+// imported — this suite runs against the BUILT chunk with no core in the process
+// — which means it is a claim about core that has to be re-read when core's list
+// changes. That is the same trade the rest of this fake makes.
+const CORE_CONTRIBUTIONS = ['team.activity', 'team.forum', 'team.notify']
+
 function fakeRg() {
   const routes = { public: [], admin: [], player: [] }
   const nav = { public: [], admin: [], player: [] }
   const providers = new Map()
   const extensions = new Map()
-  const declaredSlots = new Set()
+  const declaredSlots = new Map()
   return {
     version: '1.3.0',
     react,
@@ -74,13 +80,18 @@ function fakeRg() {
         extensions.set(slot, { id, Component })
       },
       // The INVERTED direction (core API 1.6.0): this module declares a place on
-      // its OWN page and core fills it. Core enforces the namespace, so the fake
-      // does too — a chunk that declared an unnamespaced slot would pass here and
-      // throw in a browser.
-      declareModuleSlot(id, name) {
+      // its OWN page and core fills it. Core enforces the namespace and the
+      // contribution name, so the fake does too — a chunk that declared an
+      // unnamespaced slot, or asked for a contribution core does not offer, would
+      // pass here and throw in a browser.
+      declareModuleSlot(id, name, options = {}) {
         if (!name.startsWith(`${id}.`)) throw new Error(`declareModuleSlot: "${name}" must be namespaced "${id}."`)
         if (declaredSlots.has(name)) throw new Error(`extension slot "${name}" already declared`)
-        declaredSlots.add(name)
+        const wants = options.core ?? null
+        if (wants !== null && !CORE_CONTRIBUTIONS.includes(wants)) {
+          throw new Error(`declareModuleSlot: "${name}" asks for core contribution "${wants}", which core does not offer`)
+        }
+        declaredSlots.set(name, wants)
       },
       routesFor: (area) => routes[area],
       navFor: (area) => nav[area],
@@ -209,7 +220,7 @@ it('registers under exactly one module id, matching the manifest', () => {
   assert.deepEqual([...owners], [manifest.id])
 })
 
-it('declares its own guild slots, for core to fill', () => {
+it('declares its own guild slots, each naming the core contribution it wants', () => {
   // The inverted direction (TEAMS.md Part 3). Teams are a core primitive with no
   // core page: core owns the activity feed and the forum, this module owns the
   // word "guild", so this module declares the places and core puts them in.
@@ -219,10 +230,15 @@ it('declares its own guild slots, for core to fill', () => {
   // away this module's ability to place them separately on its own page — and it
   // does place them separately, the control above the roster and the other two
   // below it.
-  assert.deepEqual([...registered.declaredSlots], [
-    'uo.guild.detail',
-    'uo.guild.forum',
-    'uo.guild.header',
+  //
+  // The second argument is what actually gets core's content here. **Core offers
+  // a contribution and never names a slot** — the first cut of this reached only
+  // this module, because core filled the literal name `uo.guild.detail` and any
+  // other game's page went empty with no error.
+  assert.deepEqual([...registered.declaredSlots.entries()], [
+    ['uo.guild.detail', 'team.activity'],
+    ['uo.guild.forum', 'team.forum'],
+    ['uo.guild.header', 'team.notify'],
   ])
 })
 
@@ -230,7 +246,7 @@ it('every declared slot is rendered by the page that owns it', () => {
   // A slot nothing renders is a slot core fills into the void. Asserted against
   // the source rather than the chunk, since the chunk is minified.
   const page = fs.readFileSync(path.resolve(HERE, '..', 'src', 'routes', 'public', 'Guild.jsx'), 'utf8')
-  for (const name of registered.declaredSlots) {
+  for (const name of registered.declaredSlots.keys()) {
     assert.match(page, new RegExp(`name="${name.replace(/\./g, '\.')}"`))
   }
 })