Stop calling every event a series

A one-time event opened for editing said "this is a recurring event —
changes apply to the whole series", and deleting one offered to delete
all occurrences of an event that has exactly one.

Three places asked whether an event had a baseEventId and took that for
recurrence. It isn't: the calendar loads its range with expandRecurrences,
and Stalwart puts a baseEventId on everything it returns that way, a
one-off pointing at itself included. The mock never sets the field at
all, which is why this only showed up against a real server.

They now share isRecurring(), which asks about recurrence rules, and
treats a base that is some other event as an occurrence of a series too
— so an expanded instance that travels without its rules is still
described honestly on the way to being deleted.

Fixes #25

web/src/store/__tests__/recurrence.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from "vitest";
+import { isRecurring } from "@/store/calendar";
+import type { CalendarEvent } from "@/jmap/types";
+
+/**
+ * `CalendarEvent/query` runs with `expandRecurrences`, and Stalwart puts a
+ * `baseEventId` on everything it returns that way — one-off events included.
+ * Treating that as proof of a series told people editing a plain event that
+ * their changes applied to the whole series, and offered to delete "all
+ * occurrences" of an event that has exactly one.
+ */
+const ev = (p: Partial<CalendarEvent>): CalendarEvent => ({ id: "ev1", "@type": "Event", uid: "u1", calendarIds: { c1: true }, start: "2026-08-25T09:00:00", duration: "PT30M", ...p } as CalendarEvent);
+
+describe("isRecurring", () => {
+  it("does not call a one-off event a series just because it has a baseEventId", () => {
+    expect(isRecurring(ev({ baseEventId: "ev1" }))).toBe(false);
+    expect(isRecurring(ev({}))).toBe(false);
+  });
+  it("still recognises an occurrence whose base is another event", () => {
+    expect(isRecurring(ev({ id: "ev1_2", baseEventId: "ev1" }))).toBe(true);
+  });
+  it("recognises a series by its recurrence rules", () => {
+    expect(isRecurring(ev({ recurrenceRules: [{ "@type": "RecurrenceRule", frequency: "weekly" }] }))).toBe(true);
+    expect(isRecurring(ev({ baseEventId: "ev1", recurrenceRules: [{ "@type": "RecurrenceRule", frequency: "daily" }] }))).toBe(true);
+    expect(isRecurring(ev({ excludedRecurrenceRules: [{ "@type": "RecurrenceRule", frequency: "monthly" }] }))).toBe(true);
+  });
+});

web/src/store/calendar.ts

@@ -297,6 +297,20 @@ export const useCalendar = create<CalendarState>((set, get) => ({
   },
 }));
 
+/**
+ * Whether an event is part of a series.
+ *
+ * Not the same question as "does it have a baseEventId": `CalendarEvent/query`
+ * runs with `expandRecurrences`, and Stalwart sets `baseEventId` on every event
+ * it returns that way — a one-off event included, pointing at itself. Recurrence
+ * rules are what make a series, so those are the question; a base that is some
+ * *other* event means this is one occurrence of one, whether or not the expanded
+ * instance carried the rules along with it.
+ */
+export function isRecurring(ev: CalendarEvent): boolean {
+  return Boolean(ev.recurrenceRules?.length || ev.excludedRecurrenceRules?.length || (ev.baseEventId && ev.baseEventId !== ev.id));
+}
+
 export function toInstance(e: CalendarEvent, calendars: Record<Id, Calendar>): EventInstance | null {
   const allDay = Boolean(e.showWithoutTime);
   let start: Date;

web/src/views/calendar/CalendarContextMenu.tsx

@@ -1,7 +1,7 @@
 import { Calendar as CalIcon, CalendarDays, Copy, ExternalLink, Palette, Pencil, Plus, Tag, Trash2, X } from "lucide-react";
 import { useLocation } from "wouter";
 import type { CalendarEvent } from "@/jmap/types";
-import { useCalendar, type EventInstance } from "@/store/calendar";
+import { useCalendar, isRecurring, type EventInstance } from "@/store/calendar";
 import { useSettings } from "@/store/settings";
 import { formatDayMonth } from "@/lib/datetime";
 import { MenuItem, MenuSep, MenuTitle, Popover, type Anchor } from "@/ui/popover";
@@ -89,7 +89,7 @@ export function CalendarContextMenu({ ctx, onClose, onOpen, onEdit, onCreate }:
   };
   const del = async () => {
     onClose();
-    const recurring = Boolean(ev.recurrenceRules?.length || ev.baseEventId);
+    const recurring = isRecurring(ev);
     if (!(await confirmDialog({ title: recurring ? "Delete all occurrences?" : "Delete this event?", confirmLabel: "Delete", danger: true }))) return;
     try {
       await cal.destroyEvent(baseId, participants > 1);

web/src/views/calendar/EventEditor.tsx

@@ -1,7 +1,7 @@
 import { useEffect, useMemo, useState } from "react";
 import { Plus, Trash2, Users } from "lucide-react";
 import type { BusyPeriod, CalendarEvent, EmailAddress, JSCalendarAlert, JSCalendarParticipant, JSCalendarRecurrenceRule, JSCalendarNDay } from "@/jmap/types";
-import { useCalendar, myParticipantKeys } from "@/store/calendar";
+import { useCalendar, myParticipantKeys, isRecurring } from "@/store/calendar";
 import { useSettings } from "@/store/settings";
 import { useSession } from "@/store/session";
 import { useContacts } from "@/store/contacts";
@@ -202,7 +202,7 @@ function EventForm({ init, base, editing, onClose, settingsTz, defaultAlert, myE
   return (
     <Dialog open onClose={onClose} title={editing ? "Edit event" : "New event"} size="lg" footer={<><button className="btn" onClick={onClose}>Cancel</button><button className="btn btn-primary" disabled={busy} onClick={() => void save()}>{busy ? "Saving…" : editing ? "Save" : attendees.length && sendInvites ? "Send invites" : "Create"}</button></>}>
       <div className="event-form">
-        {init.event?.baseEventId && <div className="info-box mb-16">This is a recurring event — changes apply to the whole series.</div>}
+        {ev && isRecurring(ev) && <div className="info-box mb-16">This is a recurring event — changes apply to the whole series.</div>}
         <div className="field"><input className="input" style={{ fontSize: "1.1em", height: 44 }} placeholder="Add title" autoFocus value={title} onChange={(e) => setTitle(e.target.value)} /></div>
         <div className="time-row mb-8">
           {allDay ? (

web/src/views/calendar/EventPopover.tsx

@@ -1,6 +1,6 @@
 import { useState } from "react";
 import { AlignLeft, Bell, Calendar as CalIcon, Check, Clock, HelpCircle, Link2, MapPin, Pencil, Repeat, Trash2, Users, X, Mail } from "lucide-react";
-import { useCalendar, myParticipantKeys, type EventInstance } from "@/store/calendar";
+import { useCalendar, myParticipantKeys, isRecurring, type EventInstance } from "@/store/calendar";
 import { Popover, type Anchor } from "@/ui/popover";
 import { confirmDialog } from "@/ui/dialog";
 import { toast } from "@/ui/toast";
@@ -29,7 +29,7 @@ export function EventPopover({ inst, anchor, onClose, onEdit }: { inst: EventIns
   const openCompose = useCompose((s) => s.open);
 
   const del = async () => {
-    const recurring = Boolean(ev.recurrenceRules?.length || ev.baseEventId);
+    const recurring = isRecurring(ev);
     const ok = await confirmDialog({ title: recurring ? "Delete all occurrences?" : "Delete this event?", message: recurring ? "This will delete the entire series." : undefined, confirmLabel: "Delete", danger: true });
     if (!ok) return;
     setBusy(true);