feat(events): a searchable source's chosen note is found when the page lacks it

A searchable source answers the editor a bounded first page, so the value an
author picked (or a template filled in) may not be on it, and its note with it.
useChosenNote asks the source for that value as a search term, once per value,
and shows the exact match's note. Found building the Rust kit warning
(PLAN_REDESIGNS §2.6), whose source - rust.options.grouppermissions - is
searchable.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

client/src/routes/admin/views/EventEditor.jsx

@@ -220,6 +220,46 @@ function SearchableOptions({ sourceId, label, disabled, onPick }) {
   )
 }
 
+/**
+ * The chosen option's note (MODULE_API 1.13.0), found even when the list the
+ * form holds does not reach it.
+ *
+ * A searchable source answers the form a bounded first page, so the value an
+ * author picked — or a template filled in — may not be in it, and its note with
+ * it. Then the source is asked for that value as a search term, once per value,
+ * and the row whose value matches exactly is the one whose note is shown. A
+ * failure is no note: advice never breaks the field it advises.
+ */
+function useChosenNote(sourceId, value, entry) {
+  const [asked, setAsked] = useState({ key: null, note: null })
+  const text = value === undefined || value === null ? '' : String(value)
+  const known = noteFor(entry, value)
+  const needAsk = Boolean(sourceId && entry?.state === 'ok' && entry.searchable && text && !known &&
+    !entry.options.some((o) => o.value === text))
+  const key = needAsk ? `${sourceId}\u0000${text}` : null
+
+  useEffect(() => {
+    if (!key || asked.key === key) return undefined
+    let alive = true
+    const timer = setTimeout(async () => {
+      try {
+        const answer = await api.admin.eventOptions(sourceId, text)
+        const row = answer?.ok ? (answer.options || []).find((o) => o.value === text) : null
+        if (alive) setAsked({ key, note: row?.note || null })
+      } catch {
+        if (alive) setAsked({ key, note: null })
+      }
+    }, 300)
+    return () => {
+      alive = false
+      clearTimeout(timer)
+    }
+  }, [key, asked.key, sourceId, text])
+
+  if (known) return known
+  return key && asked.key === key ? asked.note : null
+}
+
 /**
  * A row of buttons for a choice of two or three (Rust PLAN_REDESIGNS §2.4).
  *
@@ -366,7 +406,7 @@ function ParamField({ param, value, sourceEntry, disabled, onChange, missing, la
   // editable rather than look unset.
   const segmented = param.source && param.type !== 'boolean' && !values && isSegmentable(sourceEntry)
   const offList = segmented && asText !== '' && !sourceEntry.options.some((o) => o.value === asText)
-  const note = param.source ? noteFor(sourceEntry, value) : null
+  const note = useChosenNote(param.source, value, sourceEntry)
 
   return (
     <div style={{ marginBottom: 12 }}>