server/src/model/events/eventPublic.model.js

@@ -103,9 +103,18 @@ function phaseLabel(spec, phaseId) {
   return (phase && (phase.label || phase.id)) || null
 }
 
-/** One calendar entry, from a materialised run. */
+/**
+ * One calendar entry, from a materialised run.
+ *
+ * **`runId` is published because the event page already publishes it** on every
+ * occurrence, and `?run=` takes it. The calendar was the one public shape that
+ * named a run without saying which, so a client holding a run id from elsewhere
+ * (a module's map marker) had no way to find its event but to fetch every event
+ * page. A projection has none: nothing is committed to it.
+ */
 const publicRunEntry = (run) => ({
   kind: 'run',
+  runId: run.id,
   title: run.definition_title,
   slug: run.definition_slug,
   seriesName: run.series_name || null,

server/swagger/swagger-output.json

@@ -26295,6 +26295,23 @@
                   }
                 }
               },
+              "runId": {
+                "type": "object",
+                "properties": {
+                  "type": {
+                    "type": "string",
+                    "example": "integer"
+                  },
+                  "example": {
+                    "type": "number",
+                    "example": 3692
+                  },
+                  "description": {
+                    "type": "string",
+                    "example": "Runs only: the run this entry is, the same id `PublicEventOccurrence.runId` carries and `/events/{slug}?run=` takes. A projected entry has none, because nothing is committed to it."
+                  }
+                }
+              },
               "title": {
                 "type": "object",
                 "properties": {

server/swagger/swagger.js

@@ -1247,6 +1247,12 @@ const doc = {
           'One calendar entry. `kind` says which of two things it is: a `run` is a materialised occurrence, a `projected` entry is arithmetic past the materialisation horizon — a forecast with nothing committed to it, which a client should draw as such.',
         properties: {
           kind: { type: 'string', enum: ['run', 'projected'], example: 'run' },
+          runId: {
+            type: 'integer',
+            example: 3692,
+            description:
+              'Runs only: the run this entry is, the same id `PublicEventOccurrence.runId` carries and `/events/{slug}?run=` takes. A projected entry has none, because nothing is committed to it.',
+          },
           title: { type: 'string', example: 'The Yew Invasion' },
           slug: { type: 'string', example: 'the-yew-invasion' },
           seriesName: { type: 'string', nullable: true, example: 'The Yew Campaign' },

server/test/eventPublic.test.js

@@ -164,10 +164,32 @@ test('a calendar entry carries no operational field at all', async () => {
   // The whole security property of this file, asserted positively: the entry has
   // exactly these keys and gaining one is a deliberate act.
   assert.deepEqual(Object.keys(entry).sort(), [
-    'kind', 'live', 'scheduledFor', 'seriesName', 'seriesSlug', 'slug', 'status', 'timezone', 'title',
+    'kind', 'live', 'runId', 'scheduledFor', 'seriesName', 'seriesSlug', 'slug', 'status', 'timezone',
+    'title',
   ])
 })
 
+test('a run entry names its run, and a projection names none', async () => {
+  // Rust phase 15, D125: a map marker carries core's run id, and the app finds
+  // the event it belongs to from this calendar. The id is the one the event page
+  // already publishes on each occurrence.
+  store.definitions[0].spec = {
+    ...SPEC,
+    schedule: { kind: 'weekly', days: ['saturday'], time: '00:00' },
+  }
+  const result = await publicModel.calendar({ from: '2026-08-28', to: '2026-09-15', now: NOW })
+  const runs = result.entries.filter((e) => e.kind === 'run')
+  const projected = result.entries.filter((e) => e.kind === 'projected')
+  assert.equal(runs.length, 1)
+  assert.equal(runs[0].runId, store.runs[0].id)
+  assert.ok(projected.length > 0, 'the weekly schedule must forecast past the one run')
+  for (const entry of projected) assert.equal('runId' in entry, false)
+
+  const page = await publicModel.event('the-yew-invasion')
+  const occurrences = [page.event.current, page.event.next, ...page.event.upcoming, ...page.event.past]
+  assert.ok(occurrences.some((o) => o && o.runId === runs[0].runId))
+})
+
 test('the default window reaches back as well as forward', async () => {
   // §I: this route is "upcoming, live and recent". The default used to start at
   // `now`, which left no room for the third word — an event that finished an hour