book/02-website-module.md

@@ -147,8 +147,9 @@ statement of your dependencies, and it makes a test double for it — see
 
 ## What you register
 
-Eight calls, all synchronous, all documented in [§2.4][api]. What is worth knowing
-is not their signatures but the model behind them.
+Twelve calls — ten registrations and the two lifecycle hooks — all synchronous,
+all listed in [§2.4][api]. What is worth knowing is not their signatures but the
+model behind them.
 
 **Every call stages; nothing is committed until your whole module is known good.**
 The shape of a claim is checked at the call, so a malformed one throws with your
@@ -279,6 +280,119 @@ Every hook is awaited and none may throw past core: a subscriber's failure costs
 neither another subscriber nor the save itself. A hiccup in your sidecar breaking
 somebody's blog post edit would be a worse bug than a stale mirror.
 
+### Telling core something happened
+
+Three registrations and one call, and together they are the seam where a module
+is most tempted to reach past the boundary. The rule that keeps them safe is one
+sentence: **you declare what CAN happen; core decides who is told.**
+
+A **trigger** is not a notification stream, and the two are easy to confuse
+because both are catalogs of things that happen in your game. A stream is a
+subscribe toggle, and you publish to it yourself. A trigger is a **payload
+contract**: it names the variables an event carries and how wide an audience it
+may ever be given, an operator writes rules against it, and *core* does the
+sending. Their ids share one namespace, so declaring both for the same id is
+legal — that is one event with a toggle and a contract — while taking an id
+another module owns is not.
+
+Two fields on a trigger are worth more than their size.
+
+**`ceiling` is required and has no default, and the values are ordered by
+containment rather than by size.** It is the widest audience a rule on this
+trigger may ever be given. There is no safe value to guess: `owner` silently
+breaks a broadcast, `authenticated` silently widens something meant for staff.
+And the ladder reading of the seven values is the trap — a `staff` ceiling does
+**not** permit `owner`, because "one person" for a cheat-detection event is *the
+player it was detected on*. Fewer people is not less exposure.
+
+**`subjectKey` must name one of your declared variables**, because it is what the
+cooldown is keyed on — "once per house", not "once per user". Core checks it at
+registration and refuses the module, so this is one you meet at your first boot
+rather than in production. The check is there because the failure it prevents is
+the silent kind: a subjectKey naming nothing keys every subject on `undefined`,
+which looks exactly like the feature working right up until two houses share it.
+
+Every variable needs an `example`, and it is not decoration: it is what lets an
+operator preview and test-send a body without waiting for a real game event,
+which is the reason template systems ship untested. The type set is closed and
+has no `object` or `array` — a message that has to walk a structure has outgrown
+interpolation.
+
+An **audience** is a named set of *people* you can resolve over your own data,
+for an operator to point a rule at. "This clan's members" is one. "Everyone who
+opened the last mail" is not, and nothing here builds it.
+
+**Your resolver returns user ids and nothing else.** It is not handed a template,
+a channel or an address, and it cannot enumerate them; core maps ids to addresses
+on its own side, after preferences, suppression and the verification gate. That
+narrowness is deliberate — a module still cannot send mail, and this is the
+obvious place a back door would go. Two consequences follow from it:
+
+- **A resolver that fails resolves to NOBODY**, never to everybody and never to
+  its last good answer. Core enforces that, and your resolver should choose it
+  too, so the log can say which clan.
+- **Its params are CONSTANT.** An operator fills them in when they save the rule.
+  There is no way to say "the clan this event was about" — if a rule needs that,
+  the *event* carries its own recipients instead. This is the constraint most
+  worth knowing before you design around it rather than after.
+
+The third registration ships the **content**: the bodies your messages use and
+the rules that decide when one is sent. Both arrive **switched off**, and
+`enabled` is not a parameter. An operator turns a module's mail on; installing a
+module never does.
+
+The two halves have different lifetimes, and the asymmetry is the contract.
+**Templates re-ensure on every boot** under a seed version, so a better default
+reaches deployments that never edited it while one an operator *has* edited is
+left alone. **Rule groups are offered once, per named group key**, because
+re-offering would resurrect a rule somebody deleted and reset one they enabled.
+The consequence is easy to trip over: a rule appended to an existing group
+reaches **fresh installs only**. That is the guarantee rather than a limitation
+to route around, and a rule that must reach existing deployments takes a new
+group key. You name the groups, so the choice is yours to make knowingly.
+
+Core's generic bodies are a first-class answer rather than a fallback. Point a
+channel at `notify.event` or `inapp.event` and author nothing; ship a body of your
+own when the message has something to say that a structural projection of the
+payload cannot.
+
+**One thing in a seeded body is not checked when you register it.** The call
+asserts that `blocks` is a non-empty array and stops there; the body itself is
+validated by the block registry, which runs in the editor and in the renderer. So
+a malformed block registers cleanly, seeds cleanly, and first shows itself when an
+operator opens the body or a rule fires. Build one, open it in Admin → Engagement →
+Templates once, and you have checked the half that boot cannot.
+
+Finally the call. `ctx.events.emit(triggerId, envelope)` fires one of your own
+triggers — core binds the owner from the calling module and never reads it from
+the arguments, so there is no shape of this call that fires somebody else's
+event. It returns nothing and, in production, never throws: there is nothing a
+module could correctly do about a delivery failure from inside a game-event
+handler, so there is nothing to await. **Outside production it does throw**, at
+your call site — a payload that does not match the contract you declared is a bug
+rather than a condition, and the throw is how you meet it in your own tests
+instead of in an operator's log six weeks later.
+
+Beside it is the one call that skips the rules entirely.
+`ctx.inbox.push(userId, item)` writes a single item into a single person's on-site
+inbox. Reach for it when there is nothing for an operator to decide — a job that
+person started has finished — and for anything else use a trigger, so the message
+can be turned off, re-targeted, or sent by mail as well without a code change. The
+posture is `emit`'s: the owner is bound from the calling module, it returns
+nothing, and it will not tell you that the user has that channel switched off,
+because a module that could see that could enumerate people's preferences one
+write at a time.
+
+**Emit on the transition, not on the poll.** The template's `refresh()` runs every
+thirty seconds and emits only when the world's online state actually changed.
+Core's cooldown and hourly cap would both hold if it did not — but leaning on
+them means emitting "the world is still up" and calling it news, and the operator
+who tightens the cooldown to stop it has hidden your bug rather than fixed it.
+Two smaller traps sit inside the same function and are worth reading in
+`template/server/boot.js`: the previous state has to be read *before* the write,
+or every poll looks like no change at all, and the very first boot has no previous
+state, which is not a change either.
+
 ### Becoming the source of Teams
 
 `api.registerTeamProvider({ getTeams, getTeamMembers, getTeamLeaders })` — and

ci/core-ref.json

@@ -1,34 +1,47 @@
 {
   "repo": "https://gitea.whitlocktech.com/RunicGateway/website.git",
   "branch": "main",
-  "ref": "963d734dcc09580a7d8bb676370b4faf9b8727b2",
+  "ref": "66bb3b9a3fad01112c06f32d931c9bae56d22de6",
   "why": [
     "The core this kit is written against, pinned to a commit rather than a branch.",
-    "This one is the Teams cutover, the commit MODULE_API_VERSION 1.6.0 reached",
-    "`main` on, and 1.6.0 is what template/module.json declares. It moved here from",
-    "the 1.5.0 bump because Teams expanded the contract the book teaches: the",
-    "template now registers a Team provider and declares slots for core to fill,",
-    "and both are members that exist only at this ref and later.",
+    "This one is the engagement cutover, the commit MODULE_API_VERSION 1.9.0 reached",
+    "`main` on, and 1.9.0 is what template/module.json declares. It moved here from",
+    "1.6.0 (the Teams cutover) because engagement expanded the contract the book",
+    "teaches by three registrations and two calls: a module now declares what its",
+    "game can announce and never who is told.",
     "",
     "Moving this pin is the moment someone re-reads the chapters: CI asserts the",
     "version template/module.json declares still equals this core's",
     "MODULE_API_VERSION, so a contract bump turns this repo red on purpose",
-    "(MODULE_SYSTEM.md 2.11.1 d2, 2.10).",
+    "(MODULE_SYSTEM.md 2.11.1 d2, 2.10). Note what that means in the other",
+    "direction, because it is easy to misread as a safety net: the check clones",
+    "THIS ref, so a core that has moved past it does not turn the repo red on its",
+    "own. Nothing goes red until someone moves the pin. Between cutovers the kit is",
+    "not wrong, it is DATED - and this file is where the date is written down.",
     "",
-    "That mechanism earned its keep this time. Writing the chapters against 1.6.0",
-    "found that core's inverted-slot fills named three of module-uo's slots",
-    "literally, so the direction worked for that one module and silently did",
-    "nothing for any other game - an empty page with nothing logged. That is the",
-    "exact class of thing a book written for an audience outside this org is meant",
-    "to catch, and it was fixed in core before this pin moved.",
+    "The mechanism earned its keep again here. Writing chapter 2's engagement",
+    "section against 1.9.0 found that the seeded body a module ships is the one",
+    "thing registerEngagementSeeds does not validate - it checks that `blocks` is a",
+    "non-empty array and stops - so the template's own example body had a heading",
+    "level of 2 where the block registry takes 'h2', and no block ids at all. It",
+    "would have registered, seeded, and failed the first time an operator opened it.",
+    "Caught by running the template's register() through core's real registry at",
+    "this ref, which is what a re-read is for; both the fix and the gap are now in",
+    "the chapter and beside the code.",
+    "",
+    "That gap is also why this file's own instruction is not enough on its own. The",
+    "template job builds and tests the template against fakes and checks this",
+    "number; it does not load the module into core. A declaration a fake accepts",
+    "and core refuses would ship green, so a pin move is a run against a real core,",
+    "not just an edit here.",
     "",
     "The branch said `edge` until 2026-08-12, when the module system cut over and",
-    "that branch was deleted (MODULE_SYSTEM.md 2.9). Teams cut a second `edge` and",
-    "this pin skipped it entirely: the kit is written against what shipped, never",
-    "against what is in flight. Nothing in CI reads the branch field - it clones",
-    "the repo and checks out the sha - which is why a wrong label here would sit",
-    "unnoticed. It is for the person deciding whether a newer core is worth",
-    "re-reading the book for.",
+    "that branch was deleted (MODULE_SYSTEM.md 2.9). Two later workstreams cut an",
+    "`edge` of their own and this pin skipped both: the kit is written against what",
+    "shipped, never against what is in flight. Nothing in CI reads the branch field",
+    "- it clones the repo and checks out the sha - which is why a wrong label here",
+    "would sit unnoticed. It is for the person deciding whether a newer core is",
+    "worth re-reading the book for.",
     "",
     "Same convention as Module-uo's ci/core-ref.json, deliberately - one file, one",
     "sha, reviewable in a diff."

scripts/checkLinks.js

@@ -24,8 +24,14 @@ const { stripFences } = require('./lib/markdown')
 const ROOT = path.resolve(__dirname, '..')
 const QUIET = process.argv.includes('--quiet')
 
-// Directories that hold no prose we own.
-const SKIP_DIRS = new Set(['.git', 'node_modules', 'dist'])
+// Directories that hold no prose we own. `.core` and `core` are core's own
+// checkout: .gitignore reserves both because moving `ci/core-ref.json` means
+// cloning core in here first, and without this that clone hands the reader nine
+// broken links in somebody else's README the moment they follow the pin-bump
+// instructions. CI never saw it — the clone happens in the `template` job and
+// this check runs in `prose` — which is exactly the kind of failure that only
+// ever meets a person.
+const SKIP_DIRS = new Set(['.git', 'node_modules', 'dist', '.core', 'core'])
 
 /** Every markdown file in the repo, repo-relative, sorted. */
 function markdownFiles(dir = ROOT, out = []) {

template/README.md

@@ -112,6 +112,7 @@ backticking table names**.
 | `.gitea/workflows/release.yml` | `GITEA_HOST` and `REPO`, under the `# CHANGE THESE` banner — the only two, and they are wrong until you do. (The `.github/` flavour needs nothing: GitHub supplies `GITHUB_REPOSITORY` and friends.) |
 | `server/package.json` | package `name` and `description` |
 | `server/core.js` | the message every accessor throws |
+| `server/index.js` | the trigger, audience, template and rule-group ids — all four are namespaced with your module id, and core refuses them otherwise |
 | `server/boot.js` | the placeholder world name |
 | `server/db/schema.sql` | every table name — the prefix must be your id |
 | `server/db/purge.sql` | the same table names |
@@ -123,6 +124,7 @@ backticking table names**.
 | `server/swagger/doc.js` | the tag, and the `Examplegame…` schema prefix |
 | `server/scripts/swaggerFragment.js` | the generated fragment's `info.title` |
 | `server/test/_fakes.js` | `ctx.moduleId` |
+| `server/test/entry.test.js` | the trigger id the world-status test asserts |
 | `server/test/worldStatus.test.js` | the fixture's world name |
 | `server/test/clanProvider.test.js` | the fixture's world name |
 | `server/package-lock.json` | **regenerated** — `npm install --prefix server` |

template/module.json

@@ -2,7 +2,7 @@
   "id": "examplegame",
   "name": "Example Game",
   "version": "0.1.0",
-  "coreApi": "^1.6.0",
+  "coreApi": "^1.9.0",
   "server": "server/index.js",
   "client": { "entry": "client/dist/entry.js" },
   "schema": "server/db/schema.sql",

template/server/boot.js

@@ -52,7 +52,45 @@ async function refresh() {
   try {
     // A real module calls its sidecar's REST API here. Two hardcoded values
     // stand in, so that the page renders and the seam is visible.
-    await worldStatusDb.setStatus({ online: true, players: 0, worldName: 'Example World' })
+    const next = { online: true, players: 0, worldName: 'Example World' }
+
+    // ── Emitting a declared event ──────────────────────────────────────────
+    //
+    // **Emit on the TRANSITION, not on the poll.** This function runs every
+    // thirty seconds; a rule on an event fired every thirty seconds is a rule
+    // that mails somebody every thirty seconds. Core has a cooldown and an
+    // hourly cap and they would both hold, but leaning on them means the module
+    // is emitting "the world is still up" and calling it news. Read the previous
+    // state, compare, and emit only when the answer changed.
+    //
+    // The read is BEFORE the write for the same reason, and getting that
+    // backwards is the easy version of this bug: after `setStatus` the previous
+    // value is gone and every poll looks like no change at all — an emitter that
+    // never fires and never errors.
+    const previous = await worldStatusDb.getStatus()
+    await worldStatusDb.setStatus(next)
+
+    // `previous === null` is the first boot on a fresh install, not a change.
+    // Treating it as one would announce the world coming online to everyone the
+    // first time an operator started the site.
+    if (previous && Boolean(previous.online) !== next.online) {
+      // Fire-and-forget: no await, no return value, nothing to handle. Core
+      // validates the payload against what `index.js` declared, and what a
+      // mismatch does depends on where you are running. **In production it is
+      // dropped and logged** against this module, because a notification must
+      // never be able to break the thing it is about. **Anywhere else it throws**,
+      // at this line, so the stack points at your own call instead of at a
+      // warning nobody reads. Neither is a condition to catch: a payload that
+      // does not match the contract you declared is a bug to fix.
+      core.emit('examplegame.world.status_changed', {
+        data: {
+          worldName: next.worldName,
+          status: next.online ? 'online' : 'offline',
+          players: next.players,
+          url: '/world',
+        },
+      })
+    }
   } catch (err) {
     log.warn('could not refresh world status', { error: err.message })
   }

template/server/core.js

@@ -91,6 +91,21 @@ module.exports = {
   // stack. Routers are built inside `register()`, so `ctx` is set by then.
   get middleware() { return need().middleware },
 
+  // Firing a declared event (MODULE_API.md §2.3). Wrapped as a call rather than
+  // exposed as `get events()`, so that `require('../core').emit` taken at file
+  // scope still resolves `ctx` at call time like everything else here.
+  //
+  // **It returns nothing, and in production it never throws at the caller.** The
+  // emit is the end of this module's involvement: core validates the payload
+  // against the declared contract, decides which rules match, resolves who they
+  // reach and sends. A module cannot address a person, choose a channel or write
+  // a subject line, and this seam is deliberately too narrow to try (§2.7).
+  //
+  // Outside production a bad payload throws here rather than being logged, which
+  // is the point: you meet the mismatch in your own tests instead of in an
+  // operator's log six weeks later.
+  emit: (triggerId, envelope) => need().events.emit(triggerId, envelope),
+
   // Deployment facts. `moduleRoot` is the absolute path to `modules/<id>/` — the
   // only correct way to find a file you shipped, because the working directory is
   // core's and the module's location is the loader's business.

template/server/index.js

@@ -103,6 +103,165 @@ module.exports = function register(ctx, api) {
   // optional ones is an edit to the provider and not to this file.
   api.registerTeamProvider(clanProvider)
 
+  // ── Engagement: declaring what your game can announce ────────────────────
+  //
+  // The three calls below are one seam, and it is the one where a module is most
+  // tempted to reach past the boundary. **You declare what CAN happen; core
+  // decides who is told.** A module never names a person, a channel or an
+  // address, and never sends anything (MODULE_API 1.7.0 and 1.9.0; §2.7).
+  //
+  // A TRIGGER is not a notification stream, and the two are easy to confuse
+  // because both are catalogs of things that happen. A stream is a subscribe
+  // toggle you publish to yourself. A trigger is a PAYLOAD CONTRACT an operator
+  // writes rules against — it says what variables the event carries and how wide
+  // an audience it may ever be given, and core does the sending. Their ids share
+  // one namespace, so declaring both for one id is legal and is one event with a
+  // toggle and a contract; taking an id another module owns is not.
+  api.registerEventTriggers([
+    {
+      id: 'examplegame.world.status_changed',
+      label: 'World came up or went down',
+      description: 'The game server changed between online and offline.',
+      kind: 'event',
+      // The cooldown subject: "once per world", not "once per user". It must
+      // NAME one of the variables below — core refuses the registration
+      // otherwise, with this trigger's id in the message, and the module does not
+      // load. That check exists because the failure it prevents is silent: a
+      // subjectKey naming nothing keys every subject on `undefined`, which looks
+      // exactly like the feature working right up until two worlds share it.
+      subjectKey: 'worldName',
+      audience: 'authenticated',   // what a rule is CREATED with
+      // ...and the widest it may EVER be given. Required, with no default,
+      // because there is no safe value to guess: `owner` would silently break a
+      // broadcast and `authenticated` would silently widen a staff-only event.
+      // The values are ordered by CONTAINMENT, not by size — see chapter 2.
+      ceiling: 'authenticated',
+      version: 1,
+      variables: [
+        // Every variable needs an `example`, and it is not decoration: it is what
+        // lets an operator preview and test-send a template without waiting for a
+        // real game event, which is the reason template systems ship untested.
+        { name: 'worldName', type: 'string', required: true, example: 'Example World' },
+        { name: 'status', type: 'string', required: true, example: 'online' },
+        { name: 'players', type: 'int', required: false, example: 42 },
+        // A `url` is validated SITE-RELATIVE, because it ends up in an href in a
+        // mail somebody opens days later. Never a full URL of your own.
+        { name: 'url', type: 'url', required: false, example: '/world' },
+      ],
+    },
+  ])
+
+  // An AUDIENCE is a named set of PEOPLE this module can resolve over its own
+  // data, for an operator to point a rule at. "This clan's members" is one;
+  // "everyone who opened the last mail" is not, and nothing here builds it.
+  //
+  // **The resolver returns user ids and nothing else.** It is not handed a
+  // template, a channel or an address and it cannot enumerate them — core maps
+  // ids to addresses on its own side, after preferences, suppression and the
+  // verification gate. That is what stops this becoming the back door §2.7 spends
+  // a section closing.
+  //
+  // Audiences are their OWN id space, unlike triggers and streams: an audience
+  // names a set of people and a trigger names an event, so the two may share a
+  // name without colliding.
+  api.registerAudiences([
+    {
+      id: 'examplegame.clan.members',
+      label: 'Members of a clan',
+      // `int` or `string` only, and CONSTANT — an operator fills these in when
+      // they save the rule. There is no way to say "the clan this event was
+      // about"; if a rule needs that, the EVENT carries its own recipients
+      // instead. Finding that out late is a phase's worth of rework.
+      params: [{ id: 'clanId', type: 'string', required: true }],
+      ceiling: 'members',
+      resolve: async ({ clanId }) => clanProvider.listClanMemberUserIds({ clanId }),
+    },
+  ])
+
+  // Finally the CONTENT: the bodies your messages use, and the rules that decide
+  // when one is sent. Both arrive **switched off** — `enabled` is not a parameter
+  // and there is no call that sets it. An operator turns a module's mail on;
+  // installing a module never does.
+  //
+  // The two halves have different lifetimes, and the asymmetry is the contract:
+  //
+  //   • **Templates are re-ensured on every boot**, under `seedVersion`, so
+  //     improving a default body reaches deployments that never edited it — and
+  //     one an operator HAS edited is marked customized and left alone. Bump
+  //     `seedVersion` when the body changes; never for a comment.
+  //   • **Rule groups are offered ONCE, per named group key.** Re-offering would
+  //     resurrect a rule an operator deleted and reset one they enabled. So a rule
+  //     appended to an existing group reaches FRESH INSTALLS ONLY. That is the
+  //     guarantee rather than a limitation to work around: a rule that has to
+  //     reach existing deployments takes a NEW group key, and you choose that
+  //     knowingly because you name the groups.
+  //
+  // Core's generic bodies are a first-class answer, not a fallback: point a
+  // channel at `notify.event` / `inapp.event` / `notify.digest` and author
+  // nothing. Ship a body of your own when the message has something to say that a
+  // structural projection of the payload cannot. Below, the mail does — a world
+  // coming back deserves a sentence — and the in-app item does not, so it uses
+  // core's.
+  //
+  // Note the two casings, which are not a slip: a TEMPLATE is an object this call
+  // shapes (`triggerId`), and a RULE is a row (`trigger_id`). Copy them as they
+  // are.
+  api.registerEngagementSeeds({
+    templates: [
+      {
+        // MUST be namespaced `<moduleId>.` — the key column is unique across the
+        // whole table, and an unprefixed `notify.event` from a module would
+        // collide with core's own body and win.
+        key: 'examplegame.world-status-changed',
+        name: 'World — status changed',
+        channel: 'email',
+        subject: '{{worldName}} is {{status}}',
+        triggerId: 'examplegame.world.status_changed',
+        triggerVersion: 1,
+        seedVersion: 1,
+        // The same block objects the template editor writes, so an operator can
+        // open this in the admin panel and keep editing from here.
+        //
+        // **This is the one thing in this file core does not check for you.**
+        // `registerEngagementSeeds` asserts that `blocks` is a non-empty array and
+        // stops; the BODY is validated by the block registry, which runs in the
+        // editor and in the renderer. So a malformed block registers, seeds, and
+        // first shows itself when an operator opens the body or a rule fires.
+        // Two that are easy to get wrong: every block carries its own `id`, and
+        // `email.heading`'s `level` is 'h1' | 'h2' | 'h3' — not a number.
+        blocks: [
+          { id: 'h', type: 'email.heading', props: { level: 'h2', text: '{{worldName}} is {{status}}' } },
+          { id: 'intro', type: 'email.text', props: { text: 'There are {{players}} players online right now.' } },
+          { id: 'cta', type: 'email.button', props: { label: 'Open the world page', url: '{{url}}' } },
+        ],
+      },
+    ],
+    ruleGroups: [
+      {
+        key: 'world-v1',
+        note: 'the world status rule, seeded once',
+        rules: [
+          {
+            trigger_id: 'examplegame.world.status_changed',
+            name: 'World status changes',
+            audience: 'authenticated',
+            channels: ['email', 'inapp'],
+            template_keys: {
+              email: 'examplegame.world-status-changed',
+              inapp: 'inapp.event',
+            },
+            // Two ceilings on volume, and they answer different questions. The
+            // cooldown is per SUBJECT — one mail per world per hour, however many
+            // times it flaps. The hourly cap is per RULE, and is the thing that
+            // keeps a misconfiguration from becoming a mail storm.
+            cooldown_seconds: 3600,
+            max_sends_per_hour: 200,
+          },
+        ],
+      },
+    ],
+  })
+
   // The lifecycle hooks (§2.5). `onBoot` runs after core's schema, after this
   // module's schema fragment, and BEFORE the HTTP listener binds — so a module
   // that must not serve traffic until it has warmed a cache gets that for free.

template/server/model/clans/clanProvider.db.js

@@ -82,4 +82,25 @@ async function replaceClan({ externalId, name, abbr, memberCount, members }) {
   }
 }
 
-module.exports = { listClans, findClan, listMembers, replaceClan, CLANS, MEMBERS }
+/**
+ * The site accounts behind one clan's roster — the whole of an audience resolver.
+ *
+ * `user_id` is NULL for most characters, and the filter is the point: an audience
+ * resolves to PEOPLE WITH ACCOUNTS, and a character nobody has linked is not one.
+ * Returning its NULL would hand core a hole in an array it is about to mail.
+ *
+ * DISTINCT because one person may hold several characters in the same clan, and
+ * the resolver's contract is a set of users rather than a list of characters.
+ * Without it a three-character player is told three times.
+ */
+async function listMemberUserIds(clanId) {
+  const rows = await core.query(
+    `SELECT DISTINCT user_id AS userId
+       FROM ${MEMBERS}
+      WHERE clan_id = ? AND user_id IS NOT NULL`,
+    [clanId],
+  )
+  return rows.map((r) => r.userId)
+}
+
+module.exports = { listClans, findClan, listMembers, listMemberUserIds, replaceClan, CLANS, MEMBERS }

template/server/model/clans/clanProvider.model.js

@@ -292,6 +292,36 @@ async function projectRoster(externalId, members, viewer) {
 // a page that does not exist, which is worse.
 const pageUrlTemplate = '/examplegame/clans/{externalId}'
 
+// ── The audience resolver ─────────────────────────────────────────────────
+//
+// Registered in `index.js` as `examplegame.clan.members` and called by core when
+// a rule pointed at that audience fires. It lives beside the provider because it
+// answers a question about the same rows, and it is NOT part of the provider —
+// core calls it through the audience registry, not through the five members
+// above.
+//
+// **Three rules, and every one of them protects somebody's mailbox rather than
+// this module's correctness.**
+//
+//  1. Return user ids and nothing else. You are not handed a template, a channel
+//     or an address, and you may not enumerate them; core maps ids to addresses
+//     on its own side, after preferences, suppression and the verification gate.
+//  2. Never widen on failure. A resolver that cannot answer returns the EMPTY set
+//     — never "everyone", never the last good answer. Core treats a throw the
+//     same way, but doing it here is what lets the log say which clan.
+//  3. It is a SET of people, not a list of characters. The `DISTINCT` is in the
+//     query for that reason (see `clanProvider.db.js`).
+async function listClanMemberUserIds({ clanId }) {
+  try {
+    return await db.listMemberUserIds(clanId)
+  } catch (err) {
+    log.warn('could not resolve clan members; resolving to nobody', {
+      clanId, message: err.message,
+    })
+    return []
+  }
+}
+
 module.exports = {
   getTeams,
   getTeamMembers,
@@ -300,4 +330,5 @@ module.exports = {
   rosterVisibleTo,
   pageUrlTemplate,
   gameIsReachable,
+  listClanMemberUserIds,
 }

template/server/test/_fakes.js

@@ -49,6 +49,11 @@ function fakeCtx(overrides = {}) {
       return log
     },
     auth: { getUserFromRequest: spy(null) },
+    // The engagement seam (§2.3). One method, recording, because that is the
+    // whole of what a module may do with it: fire a declared event and stop.
+    // Core's own emit is fire-and-forget and returns nothing, so this does too —
+    // a fake that returned a receipt would invite a module to wait on one.
+    events: { emit: spy(undefined) },
     middleware: {
       requireAuth: (req, res, next) => next(),
       requireRole: () => (req, res, next) => next(),
@@ -85,7 +90,10 @@ function fakeCtx(overrides = {}) {
  * an operator's install.
  */
 function fakeApi() {
-  const record = { routes: null, extensions: [], streams: null, legs: [], hooks: {}, teamProvider: null }
+  const record = {
+    routes: null, extensions: [], streams: null, legs: [], hooks: {}, teamProvider: null,
+    triggers: null, audiences: null, engagementSeeds: null,
+  }
   const called = new Set()
   const once = (name) => {
     if (called.has(name)) throw new Error(`${name}() called twice`)
@@ -103,6 +111,9 @@ function fakeApi() {
     // module registering a provider collides with the first. A fake cannot see
     // the second module, and asserting the half it can see is still worth doing.
     registerTeamProvider(provider) { once('registerTeamProvider'); record.teamProvider = provider },
+    registerEventTriggers(triggers) { once('registerEventTriggers'); record.triggers = triggers },
+    registerAudiences(audiences) { once('registerAudiences'); record.audiences = audiences },
+    registerEngagementSeeds(seeds) { once('registerEngagementSeeds'); record.engagementSeeds = seeds },
     onBoot(fn) { once('onBoot'); record.hooks.onBoot = fn },
     onShutdown(fn) { once('onShutdown'); record.hooks.onShutdown = fn },
   }

template/server/test/entry.test.js

@@ -130,3 +130,163 @@ test('the manifest declares what the loader requires', () => {
   // serves, so an entry in the module root would publish the whole module.
   if (manifest.client) assert.ok(manifest.client.entry.includes('/'), 'client.entry must be in a subdirectory')
 })
+
+// ── The engagement seam ───────────────────────────────────────────────────
+//
+// Core validates most of what is declared here at registration, and a module
+// that gets it wrong does not load. These tests are mostly NOT that validator
+// restated: they are the rules a module can satisfy at boot and still have got
+// WRONG in a way whose only symptom is mail somebody received. Where one does
+// overlap core — the namespacing and subjectKey assertions below — it is because
+// `npm test` is a cheaper place to meet the failure than a first boot, and the
+// message here names the field.
+
+test('every declared trigger is namespaced, ceilinged, and carries examples', () => {
+  const { api } = register()
+  const triggers = api.record.triggers
+  assert.ok(Array.isArray(triggers) && triggers.length, 'no triggers were declared')
+
+  for (const t of triggers) {
+    // Trigger ids and notification-stream ids are ONE namespace, so an id must
+    // carry this module's own prefix or it is a claim on somebody else's.
+    assert.ok(t.id.startsWith(`${manifest.id}.`), `${t.id} is not namespaced`)
+
+    // `ceiling` is required and has no default: there is no safe value to guess.
+    assert.ok(t.ceiling, `${t.id} declares no ceiling`)
+
+    // Core refuses this one too; failing it here just costs less. What the rule
+    // protects is the cooldown key — "once per world", not "once per user" — and
+    // a subjectKey naming nothing would key every subject on `undefined`.
+    const names = t.variables.map((v) => v.name)
+    assert.ok(names.includes(t.subjectKey), `${t.id}: subjectKey "${t.subjectKey}" is not a variable`)
+
+    for (const v of t.variables) {
+      // Not decoration: the example is what makes a template previewable and
+      // test-sendable without waiting for a real game event.
+      assert.ok('example' in v, `${t.id}.${v.name} has no example`)
+      // The type set is closed. A payload that needs a structure has outgrown
+      // interpolation, and a template cannot walk one.
+      assert.ok(
+        ['string', 'int', 'float', 'boolean', 'datetime', 'url'].includes(v.type),
+        `${t.id}.${v.name} has type "${v.type}"`,
+      )
+      // A url is site-relative, because it ends up in an href in a mail somebody
+      // opens days later.
+      if (v.type === 'url') assert.match(v.example, /^\/[^/]/, `${t.id}.${v.name} must be site-relative`)
+    }
+  }
+})
+
+test('an audience resolves to nobody rather than to everybody when it fails', async () => {
+  const ctx = fakeCtx({ db: { query: () => Promise.reject(new Error('database is down')), pool: {} } })
+  const { api } = register(ctx)
+  const audience = api.record.audiences[0]
+
+  // The one behaviour worth a test of its own. Core treats a throw the same way,
+  // so this is not core's guard restated — it is the module choosing the same
+  // answer deliberately, and the reason is that the alternatives are both worse:
+  // "everyone" mails the wrong people and a stale answer mails yesterday's.
+  assert.deepStrictEqual(await audience.resolve({ clanId: 'clan-1' }), [])
+})
+
+test('a seeded rule names only this module’s triggers, and its own or core’s templates', () => {
+  const { api } = register()
+  const seeds = api.record.engagementSeeds
+  const ownKeys = new Set(seeds.templates.map((t) => t.key))
+  const coreKeys = new Set(['notify.event', 'inapp.event', 'notify.digest'])
+
+  for (const t of seeds.templates) {
+    // The key column is UNIQUE across the whole table, so an unprefixed
+    // `notify.event` from a module would collide with core's body and win.
+    assert.ok(t.key.startsWith(`${manifest.id}.`), `template ${t.key} is not namespaced`)
+    // `protected` means "the system breaks without this body" — true of a
+    // password reset and of nothing a module ships. Core refuses a module
+    // template that sets it, because it would take an operator's delete button
+    // away.
+    assert.ok(!('protected' in t), `template ${t.key} may not mark itself protected`)
+  }
+
+  for (const group of seeds.ruleGroups) {
+    for (const rule of group.rules) {
+      assert.ok(
+        api.record.triggers.some((t) => t.id === rule.trigger_id),
+        `${rule.name} names a trigger this module does not declare`,
+      )
+      for (const key of Object.values(rule.template_keys)) {
+        assert.ok(ownKeys.has(key) || coreKeys.has(key), `${rule.name} names an unknown template ${key}`)
+      }
+      // `enabled` is not a parameter, and a value passed for it is ignored
+      // rather than refused. Passing one anyway states an intention the platform
+      // will not honour, so the honest thing is not to write it.
+      assert.ok(!('enabled' in rule), `${rule.name} may not seed itself enabled`)
+    }
+  }
+})
+
+test('every seeded body is a shape the block registry will accept', () => {
+  const { api } = register()
+
+  // The gap this exists for: `registerEngagementSeeds` checks that `blocks` is a
+  // non-empty array and stops. The BODY is validated by core's block registry,
+  // which runs in the template editor and in the renderer — so a malformed block
+  // registers, seeds, and first shows itself when an operator opens the body or a
+  // rule fires. Core is not here to ask, so assert the two rules that are easy to
+  // get wrong and impossible to notice.
+  const HEADING_LEVELS = ['h1', 'h2', 'h3']
+
+  for (const t of api.record.engagementSeeds.templates) {
+    const ids = new Set()
+    for (const block of t.blocks) {
+      // Every block carries its own id, unique within the body: it is how the
+      // editor addresses one block, and how `inapp.event`'s renderer maps blocks
+      // onto the inbox row's columns by role.
+      assert.ok(block.id && typeof block.id === 'string', `${t.key}: a block has no id`)
+      assert.ok(!ids.has(block.id), `${t.key}: two blocks share the id "${block.id}"`)
+      ids.add(block.id)
+      assert.ok(block.type.startsWith('email.'), `${t.key}: ${block.type} is not an email block`)
+
+      // A heading's `level` is a SIZE token, not a number. `{ level: 2 }` reads
+      // perfectly and is refused, and it renders at the default size in any
+      // preview that skips validation — which is the whole trap.
+      if (block.type === 'email.heading') {
+        assert.ok(
+          HEADING_LEVELS.includes(block.props.level),
+          `${t.key}: heading level "${block.props.level}" must be one of ${HEADING_LEVELS.join(', ')}`,
+        )
+      }
+    }
+  }
+})
+
+test('the world event fires on the transition and not on the poll', async () => {
+  const boot = require('../boot')
+
+  // Online already, and reporting online again. The refresh writes, and nothing
+  // is announced: this runs every thirty seconds, and a rule on an event fired
+  // every thirty seconds mails somebody every thirty seconds. Core's cooldown
+  // would hold — but leaning on it means emitting "still up" and calling it news.
+  const steady = fakeCtx({ db: { query: () => Promise.resolve([{ online: 1 }]), pool: {} } })
+  require('../core')._reset()
+  require('../core').init(steady)
+  await boot.refresh()
+  assert.deepStrictEqual(steady.events.emit.calls, [])
+
+  // Offline before, online now. One emit, with the declared payload.
+  const flipped = fakeCtx({ db: { query: () => Promise.resolve([{ online: 0 }]), pool: {} } })
+  require('../core')._reset()
+  require('../core').init(flipped)
+  await boot.refresh()
+  assert.strictEqual(flipped.events.emit.calls.length, 1)
+  const [triggerId, envelope] = flipped.events.emit.calls[0]
+  assert.strictEqual(triggerId, 'examplegame.world.status_changed')
+  assert.strictEqual(envelope.data.status, 'online')
+
+  // A fresh install, where there is no previous row at all. Not a change — and
+  // announcing it would tell everyone the world came online the first time an
+  // operator started the site.
+  const fresh = fakeCtx({ db: { query: () => Promise.resolve([]), pool: {} } })
+  require('../core')._reset()
+  require('../core').init(fresh)
+  await boot.refresh()
+  assert.deepStrictEqual(fresh.events.emit.calls, [])
+})