fix(modules): core offers a contribution, never a slot name

The inverted slot direction reached exactly one module. Core filled three
literal names - uo.guild.detail, uo.guild.forum, uo.guild.header - matched by
exact name in applyCoreFills, so a second game declaring a place under its own
id got an empty page and no error. "A fill for a slot nobody declared is not an
error" is the rule that made the miss invisible, and it is the right rule; what
was wrong was core knowing a slot's name at all.

It also put a module identifier inside core, in three string literals
scripts/checkModuleIdentifiers.js masks by construction and could never catch.

Found by the integration kit while writing the chapter that teaches this shape
to an audience outside this org - which is what that phase is for.

So the module says WHERE, in its own vocabulary, and WHICH of core's
contributions goes there:

  declareModuleSlot(ID, 'uo.guild.detail', { core: 'team.activity' })

and core offers into the catalogue rather than into a name:

  offerCoreFill('team.activity', TeamActivityFeed)

CORE_CONTRIBUTIONS is exported and fixed at build time, so asking for one core
does not offer THROWS at the declaration. That asymmetry with an unfilled slot
is deliberate: an unknown contribution is always a typo or a version skew - the
module's coreApi range has already been checked - and the failure it would
otherwise produce is a page that renders empty forever with nothing logged.

options.core is optional; a slot that asks for nothing stays empty, which is
what a module declaring a place it fills itself wants. More than one slot may
ask for the same contribution and each gets it: how many places a module wants
its feed in is a layout decision on a page core does not own.

Amends MODULE_API 1.6.0 in place rather than adding 1.7.0 - the same rule the
eighth and ninth members were given, and 1.6.0 has only ever been on edge.

Also: the UI kit is nine exports, not eight. Slot made it nine in phase 3 and
the comment beside it still said eighth.

288 client tests, 1162 server tests.

Co-Authored-By: Claude <noreply@anthropic.com>

client/test/moduleSlots.test.js

@@ -5,7 +5,8 @@ import {
   registry,
   declareSlot,
   declareModuleSlot,
-  fillModuleSlot,
+  offerCoreFill,
+  CORE_CONTRIBUTIONS,
   applyCoreFills,
   registerExtension,
   extensionFor,
@@ -112,34 +113,72 @@ test('a module-declared slot must be namespaced under the declaring module', ()
   assert.doesNotThrow(() => declareModuleSlot('uo', 'uo.guild.detail'))
 })
 
-test('core fills a module slot only after the module has declared it', () => {
-  // The ordering that makes this a separate call: core's bundle evaluates BEFORE
-  // any module chunk, so at the moment core registers its fill the slot does not
-  // exist yet. Filling eagerly would silently do nothing.
-  fillModuleSlot('uo.guild.detail', Feed)
-  assert.equal(extensionFor('uo.guild.detail'), null, 'not filled before the module declared it')
-
-  declareModuleSlot('uo', 'uo.guild.detail')
-  assert.equal(extensionFor('uo.guild.detail'), null, 'and not before the fills are applied')
+test('core offers a contribution and the module says where it goes', () => {
+  // The ordering that makes this two calls: core's bundle evaluates BEFORE any
+  // module chunk, so at the moment core offers, no module-declared slot exists.
+  offerCoreFill('team.activity', Feed)
+  declareModuleSlot('uo', 'uo.guild.detail', { core: 'team.activity' })
+  assert.equal(extensionFor('uo.guild.detail'), null, 'not before the fills are applied')
 
   applyCoreFills()
   assert.equal(extensionFor('uo.guild.detail'), Feed)
 })
 
-test('a fill for a slot nobody declared is not an error', () => {
-  // The module is not installed. Core offering content for a page that does not
-  // exist is the ordinary case on any deployment, not a misconfiguration — the
-  // mirror of an unfilled slot rendering nothing.
-  fillModuleSlot('rust.clan.detail', Feed)
+test('core names no slot, so a second game gets the same content in its own words', () => {
+  // The defect this replaced: core used to fill three literal `uo.guild.*` names,
+  // which reached exactly one module. Every other game declared a place under its
+  // own id and got an empty page with no error, because a fill nobody declared is
+  // deliberately not an error — the rule that makes an unknown name invisible.
+  offerCoreFill('team.activity', Feed)
+  declareModuleSlot('examplegame', 'examplegame.clan.detail', { core: 'team.activity' })
+  applyCoreFills()
+  assert.equal(extensionFor('examplegame.clan.detail'), Feed)
+})
+
+test('two modules can ask for the same contribution, and both get it', () => {
+  // Core has no reason to care how many places want its feed, and refusing the
+  // second would be core making a layout decision on a page it does not own.
+  offerCoreFill('team.activity', Feed)
+  declareModuleSlot('uo', 'uo.guild.detail', { core: 'team.activity' })
+  declareModuleSlot('uo', 'uo.guild.summary', { core: 'team.activity' })
+  applyCoreFills()
+  assert.equal(extensionFor('uo.guild.detail'), Feed)
+  assert.equal(extensionFor('uo.guild.summary'), Feed)
+})
+
+test('a slot that asks for nothing stays empty', () => {
+  // Optional on purpose: a module may declare a place it fills itself, or one it
+  // is keeping for later. Neither is core's business.
+  offerCoreFill('team.activity', Feed)
+  declareModuleSlot('uo', 'uo.guild.detail')
+  applyCoreFills()
+  assert.equal(extensionFor('uo.guild.detail'), null)
+})
+
+test('asking for a contribution core does not offer THROWS', () => {
+  // The asymmetry with an unfilled slot, and it is deliberate. An unknown
+  // contribution is always a typo or a version skew — core's list is fixed at
+  // build time and the module's coreApi range has already been checked — and the
+  // alternative failure is a page that renders empty forever with nothing logged.
+  assert.throws(
+    () => declareModuleSlot('uo', 'uo.guild.detail', { core: 'team.activityfeed' }),
+    /does not offer/,
+  )
+  assert.ok(CORE_CONTRIBUTIONS['team.activity'], 'the catalogue is exported so a test can name it')
+})
+
+test('a contribution nothing asks for is not an error', () => {
+  // No game module installed. Core offering content for a page that does not
+  // exist is the ordinary case on any deployment, not a misconfiguration.
+  offerCoreFill('team.forum', Feed)
   assert.doesNotThrow(() => applyCoreFills())
-  assert.equal(extensionFor('rust.clan.detail'), null)
 })
 
 test('a module that fills its own slot first keeps it', () => {
   const Own = () => null
-  declareModuleSlot('uo', 'uo.guild.detail')
+  declareModuleSlot('uo', 'uo.guild.detail', { core: 'team.activity' })
   registerExtension('uo', 'uo.guild.detail', Own)
-  fillModuleSlot('uo.guild.detail', Feed)
+  offerCoreFill('team.activity', Feed)
   applyCoreFills()
   assert.equal(extensionFor('uo.guild.detail'), Own, 'first fill wins, as everywhere else')
 })
@@ -150,21 +189,21 @@ test('a module-declared slot cannot be declared twice', () => {
 })
 
 test('applying the fills twice does not re-fill or throw', () => {
-  declareModuleSlot('uo', 'uo.guild.detail')
-  fillModuleSlot('uo.guild.detail', Feed)
+  declareModuleSlot('uo', 'uo.guild.detail', { core: 'team.activity' })
+  offerCoreFill('team.activity', Feed)
   applyCoreFills()
   assert.doesNotThrow(() => applyCoreFills())
   assert.equal(extensionFor('uo.guild.detail'), Feed)
 })
 
-test('a non-component fill is refused at the call site, not at render', () => {
-  assert.throws(() => fillModuleSlot('uo.guild.detail', 'nope'), /is not a component/)
+test('a non-component contribution is refused at the call site, not at render', () => {
+  assert.throws(() => offerCoreFill('team.activity', 'nope'), /is not a component/)
 })
 
 test('_reset clears pending fills, so one test cannot leak into the next', () => {
-  fillModuleSlot('uo.guild.detail', Feed)
+  offerCoreFill('team.activity', Feed)
   _reset()
-  declareModuleSlot('uo', 'uo.guild.detail')
+  declareModuleSlot('uo', 'uo.guild.detail', { core: 'team.activity' })
   applyCoreFills()
   assert.equal(extensionFor('uo.guild.detail'), null)
 })