fix: fix minor bugs

src/plugins/built-in/timetable/CalendarSyncControl.svelte

@@ -669,22 +669,27 @@
 </div>
 
 {#snippet googleIcon()}
-  <svg viewBox="0 0 24 24">
+  <svg
+    xmlns="http://www.w3.org/2000/svg"
+    viewBox="-3 0 262 262"
+    preserveAspectRatio="xMidYMid"
+    aria-hidden="true"
+  >
     <path
+      d="M255.878 133.451c0-10.734-.871-18.567-2.756-26.69H130.55v48.448h71.947c-1.45 12.04-9.283 30.172-26.69 42.356l-.244 1.622 38.755 30.023 2.685.268c24.659-22.774 38.875-56.282 38.875-96.027"
       fill="#4285F4"
-      d="M22 12c0-.96-.08-1.88-.24-2.76H12v5.22h5.68c-.24 1.28-.96 2.44-2.04 3.18v2.64h3.3c1.92-1.76 3.06-4.36 3.06-7.28z"
     />
     <path
+      d="M130.55 261.1c35.248 0 64.839-11.605 86.453-31.622l-41.196-31.913c-11.024 7.688-25.82 13.055-45.257 13.055-34.523 0-63.824-22.773-74.269-54.25l-1.531.13-40.298 31.187-.527 1.465C35.393 231.798 79.49 261.1 130.55 261.1"
       fill="#34A853"
-      d="M12 22c2.76 0 5.08-.92 6.78-2.5l-3.3-2.64c-.92.62-2.1.98-3.48.98-2.68 0-4.96-1.8-5.78-4.22H2.18v2.72A10 10 0 0 0 12 22z"
     />
     <path
+      d="M56.281 156.37c-2.756-8.123-4.351-16.827-4.351-25.82 0-8.994 1.595-17.697 4.206-25.82l-.073-1.73L15.26 71.312l-1.335.635C5.077 89.644 0 109.517 0 130.55s5.077 40.905 13.925 58.602l42.356-32.782"
       fill="#FBBC05"
-      d="M6.22 13.62A5.98 5.98 0 0 1 5.82 12c0-.56.1-1.1.28-1.62V7.66H2.18A10 10 0 0 0 2 12c0 1.62.38 3.16 1.06 4.52l3.16-2.9z"
     />
     <path
-      fill="#EA4335"
-      d="M12 5.38c1.5 0 2.84.52 3.9 1.54l2.92-2.92C17.08 2.34 14.76 1.2 12 1.2 7.54 1.2 3.72 3.94 2.18 7.66l4.04 3.14c.82-2.42 3.1-4.22 5.78-4.22z"
+      d="M130.55 50.479c24.514 0 41.05 10.589 50.479 19.438l36.844-35.974C195.245 12.91 165.798 0 130.55 0 79.49 0 35.393 29.301 13.925 71.947l42.211 32.783c10.59-31.477 39.891-54.251 74.414-54.251"
+      fill="#EB4335"
     />
   </svg>
 {/snippet}

src/seqta/utils/calendarSync/lessonSyncShared.test.ts

@@ -11,8 +11,10 @@ import {
 } from "./eventFingerprint";
 import {
   buildLessonSyncResult,
+  collectOriginDeleteEntries,
   entriesToPrune,
   formatLessonSyncResultMessage,
+  mapPool,
   mergeRemoteEventsIntoMap,
   reportSyncProgress,
   upsertLessonEvents,
@@ -166,6 +168,45 @@ describe("mergeRemoteEventsIntoMap", () => {
   });
 });
 
+describe("collectOriginDeleteEntries", () => {
+  const origin = "https://school.seqta.com.au";
+  const mapKey = (o: string, seqtaKey: string) => `${o}::${seqtaKey}`;
+
+  it("includes local map entries and matching remote events", () => {
+    const eventMap = {
+      [`${origin}::${origin}:cal:1`]: { id: "local-1", date: "2026-07-13" },
+    };
+    const entries = collectOriginDeleteEntries(
+      eventMap,
+      origin,
+      [
+        {
+          seqtaKey: `${origin}:cal:2`,
+          id: "remote-2",
+          date: "2026-07-14",
+          fingerprint: "fp",
+        },
+        {
+          seqtaKey: "",
+          id: "orphan-3",
+          date: "2026-07-15",
+          fingerprint: "fp",
+        },
+        {
+          seqtaKey: "https://other.seqta.com.au:cal:9",
+          id: "other",
+          date: "2026-07-15",
+          fingerprint: "fp",
+        },
+      ],
+      mapKey,
+    );
+
+    const ids = entries.map(([, id]) => id).sort();
+    expect(ids).toEqual(["local-1", "orphan-3", "remote-2"]);
+  });
+});
+
 describe("formatLessonSyncResultMessage", () => {
   it("includes unchanged counts", () => {
     expect(
@@ -222,4 +263,61 @@ describe("upsertLessonEvents skip unchanged", () => {
     expect(upsert).not.toHaveBeenCalled();
     expect(result).toMatchObject({ created: 0, updated: 0, skipped: 1, failed: 0 });
   });
+
+  it("runs upserts concurrently", async () => {
+    const origin = "https://school.seqta.com.au";
+    let inFlight = 0;
+    let maxInFlight = 0;
+    const events = Array.from({ length: 6 }, (_, i) => ({
+      seqtaKey: `${origin}:cal:${i}`,
+      summary: `Class ${i}`,
+      description: "Synced by BetterSEQTA+",
+      startDateTime: "2026-07-13T09:00:00",
+      endDateTime: "2026-07-13T10:00:00",
+      timeZone: "UTC",
+    }));
+
+    const upsert = jest.fn(async () => {
+      inFlight += 1;
+      maxInFlight = Math.max(maxInFlight, inFlight);
+      await new Promise((resolve) => setTimeout(resolve, 30));
+      inFlight -= 1;
+      return `id-${Math.random()}`;
+    });
+
+    const result = await upsertLessonEvents({
+      events,
+      eventMap: {},
+      origin,
+      staleEntryCount: 0,
+      totalSteps: events.length,
+      lastSyncAt: Date.now(),
+      initialFailed: 0,
+      getAccessToken: async () => "token",
+      mapKey: (o, k) => `${o}::${k}`,
+      upsert,
+      writeState: async () => undefined,
+      logLabel: "Test",
+      concurrency: 2,
+    });
+
+    expect(result.created).toBe(6);
+    expect(upsert).toHaveBeenCalledTimes(6);
+    expect(maxInFlight).toBeGreaterThan(1);
+    expect(maxInFlight).toBeLessThanOrEqual(2);
+  });
+});
+
+describe("mapPool", () => {
+  it("limits concurrency", async () => {
+    let inFlight = 0;
+    let maxInFlight = 0;
+    await mapPool([1, 2, 3, 4, 5], 2, async () => {
+      inFlight += 1;
+      maxInFlight = Math.max(maxInFlight, inFlight);
+      await new Promise((resolve) => setTimeout(resolve, 20));
+      inFlight -= 1;
+    });
+    expect(maxInFlight).toBe(2);
+  });
 });

src/seqta/utils/calendarSync/lessonSyncShared.ts

@@ -22,6 +22,34 @@ import type {
 
 export const EVENT_MAP_PERSIST_EVERY = 10;
 
+/** Max concurrent Google/Outlook create/update/delete requests during sync. */
+export const SYNC_CONCURRENCY = 2;
+
+/** Same cap for deletes to avoid provider rate limits. */
+export const SYNC_DELETE_CONCURRENCY = 2;
+
+/** Run async work over items with a fixed concurrency pool. */
+export async function mapPool<T>(
+  items: readonly T[],
+  concurrency: number,
+  worker: (item: T, index: number) => Promise<void>,
+): Promise<void> {
+  if (items.length === 0) return;
+  const limit = Math.max(1, Math.min(concurrency, items.length));
+  let nextIndex = 0;
+
+  async function runWorker(): Promise<void> {
+    while (true) {
+      const index = nextIndex;
+      nextIndex += 1;
+      if (index >= items.length) return;
+      await worker(items[index], index);
+    }
+  }
+
+  await Promise.all(Array.from({ length: limit }, () => runWorker()));
+}
+
 export type MappedLessonEvent = {
   seqtaKey: string;
   summary: string;
@@ -104,6 +132,41 @@ export function mergeRemoteEventsIntoMap(
   }
 }
 
+/**
+ * Build a deduped delete list from local map + remote events for an origin.
+ * Unkeyed remote events (empty seqtaKey) are included as orphan removals.
+ */
+export function collectOriginDeleteEntries(
+  eventMap: EventMapRecord,
+  origin: string,
+  remoteEvents: RemoteSyncedEvent[],
+  mapKey: (origin: string, seqtaKey: string) => string,
+): Array<[string, string]> {
+  const byId = new Map<string, string>();
+
+  for (const [key, id] of originEventMapEntries(eventMap, origin)) {
+    byId.set(id, key);
+  }
+
+  for (const remote of remoteEvents) {
+    if (remote.seqtaKey && !remote.seqtaKey.startsWith(origin)) continue;
+    if (byId.has(remote.id)) continue;
+    const key = remote.seqtaKey
+      ? mapKey(origin, remote.seqtaKey)
+      : `${origin}::__orphan__:${remote.id}`;
+    byId.set(remote.id, key);
+  }
+
+  return Array.from(byId.entries()).map(([id, key]) => [key, id]);
+}
+
+export function clearOriginEventMapEntries(eventMap: EventMapRecord, origin: string): void {
+  const prefix = `${origin}::`;
+  for (const key of Object.keys(eventMap)) {
+    if (key.startsWith(prefix)) delete eventMap[key];
+  }
+}
+
 export function reconcileRangeForMode(
   mode: "full" | "incremental",
   weeksAhead: number,
@@ -184,6 +247,7 @@ export async function deleteTrackedLessonEvents(
     progressOffset?: number;
     progressTotal?: number;
     logLabel: string;
+    concurrency?: number;
   },
 ): Promise<{ deleted: number; failed: number }> {
   if (entries.length === 0) return { deleted: 0, failed: 0 };
@@ -194,18 +258,22 @@ export async function deleteTrackedLessonEvents(
     progressOffset = 0,
     progressTotal = 0,
     logLabel,
+    concurrency = SYNC_DELETE_CONCURRENCY,
   } = options;
 
   let accessToken = await getAccessToken();
-  let deleted = 0;
-  let failed = 0;
-
-  for (const [mapKey, eventId] of entries) {
-    try {
-      await deleteEvent(accessToken, eventId, async () => {
+  const refreshAccessToken = async () => {
     accessToken = await getAccessToken();
     return accessToken;
-      });
+  };
+  let deleted = 0;
+  let failed = 0;
+  let completed = 0;
+  let persistChain: Promise<unknown> = Promise.resolve();
+
+  await mapPool(entries, concurrency, async ([mapKey, eventId]) => {
+    try {
+      await deleteEvent(accessToken, eventId, refreshAccessToken);
       delete eventMap[mapKey];
       deleted += 1;
     } catch (err) {
@@ -213,16 +281,22 @@ export async function deleteTrackedLessonEvents(
       failed += 1;
     }
 
+    completed += 1;
     reportSyncProgress(onProgress, {
       phase: "deleting",
-      current: progressOffset + deleted + failed,
+      current: progressOffset + completed,
       total: progressTotal,
-      message: `Removing old events (${deleted + failed}/${entries.length})…`,
+      message: `Removing old events (${completed}/${entries.length})…`,
     });
 
-    if (persistProgress && (deleted + failed) % EVENT_MAP_PERSIST_EVERY === 0) {
-      await writeState({ eventMap });
+    if (persistProgress && completed % EVENT_MAP_PERSIST_EVERY === 0) {
+      persistChain = persistChain.then(() => writeState({ eventMap }));
+      await persistChain;
     }
+  });
+
+  if (persistProgress) {
+    await persistChain;
   }
 
   return { deleted, failed };
@@ -276,6 +350,7 @@ type UpsertLessonEventsParams<TEvent extends MappedLessonEvent> = {
   }) => Promise<unknown>;
   onProgress?: GoogleCalendarSyncOptions["onProgress"];
   logLabel: string;
+  concurrency?: number;
 };
 
 export async function upsertLessonEvents<TEvent extends MappedLessonEvent>(
@@ -301,38 +376,38 @@ export async function upsertLessonEvents<TEvent extends MappedLessonEvent>(
     writeState,
     onProgress,
     logLabel,
+    concurrency = SYNC_CONCURRENCY,
   } = params;
 
   let accessToken = await getAccessToken();
+  const refreshAccessToken = async () => {
+    accessToken = await getAccessToken();
+    return accessToken;
+  };
   let created = 0;
   let updated = 0;
   let skipped = 0;
   let failed = initialFailed;
+  let completed = 0;
+  let persistChain: Promise<unknown> = Promise.resolve();
 
-  for (let i = 0; i < events.length; i++) {
-    const event = events[i];
+  const persistState = () => {
+    persistChain = persistChain.then(() =>
+      writeState({ eventMap, lastSyncAt, lastSyncOrigin: origin }),
+    );
+    return persistChain;
+  };
+
+  await mapPool(events, concurrency, async (event) => {
     const key = mapKey(origin, event.seqtaKey);
     const existingId = getStoredEventId(eventMap[key]);
     const desiredFingerprint = eventFingerprint(event);
-    const progressCurrent = staleEntryCount + i + 1;
-    const progressMessage = `Syncing events (${i + 1}/${events.length})…`;
 
     try {
       if (existingId && getStoredFingerprint(eventMap[key]) === desiredFingerprint) {
         skipped += 1;
-        reportSyncProgress(onProgress, {
-          phase: "upserting",
-          current: progressCurrent,
-          total: totalSteps,
-          message: progressMessage,
-        });
-        continue;
-      }
-
-      const remoteId = await upsert(accessToken, existingId, event, async () => {
-        accessToken = await getAccessToken();
-        return accessToken;
-      });
+      } else {
+        const remoteId = await upsert(accessToken, existingId, event, refreshAccessToken);
         if (existingId) updated += 1;
         else created += 1;
         eventMap[key] = {
@@ -340,21 +415,27 @@ export async function upsertLessonEvents<TEvent extends MappedLessonEvent>(
           date: lessonDateForEvent(event.startDateTime, event.seqtaKey),
           fingerprint: desiredFingerprint,
         };
-
-      if ((i + 1) % EVENT_MAP_PERSIST_EVERY === 0 || i === events.length - 1) {
-        await writeState({ eventMap, lastSyncAt, lastSyncOrigin: origin });
       }
     } catch (err) {
       verboseLog(`[BetterSEQTA+] ${logLabel} event sync failed:`, err);
       failed += 1;
     }
 
+    completed += 1;
     reportSyncProgress(onProgress, {
       phase: "upserting",
-      current: progressCurrent,
+      current: staleEntryCount + completed,
       total: totalSteps,
-      message: progressMessage,
+      message: `Syncing events (${completed}/${events.length})…`,
     });
+
+    if (completed % EVENT_MAP_PERSIST_EVERY === 0) {
+      await persistState();
+    }
+  });
+
+  if (events.length > 0) {
+    await persistState();
   }
 
   return { created, updated, skipped, failed, accessToken };

src/seqta/utils/calendarSync/remoteEvents.ts

@@ -16,20 +16,47 @@ export type RemoteSyncedEvent = {
   date: string;
 };
 
+export type ListSyncedEventsOptions = {
+  /** Include category/calendar events that are missing a seqta key (legacy orphans). */
+  includeUnkeyed?: boolean;
+};
+
+const MAX_RETRIES = 4;
+
+function sleep(ms: number): Promise<void> {
+  return new Promise((resolve) => setTimeout(resolve, ms));
+}
+
+function isRetryableStatus(status: number): boolean {
+  return status === 429 || status === 500 || status === 502 || status === 503 || status === 403;
+}
+
 async function authorizedFetch(
   accessToken: string,
   url: string,
   init: RequestInit,
   refreshAccessToken?: () => Promise<string>,
 ): Promise<Response> {
+  let token = accessToken;
+  for (let attempt = 0; attempt < MAX_RETRIES; attempt++) {
     const res = await fetch(url, {
       ...init,
-    headers: { Authorization: `Bearer ${accessToken}`, ...init.headers },
+      headers: { Authorization: `Bearer ${token}`, ...init.headers },
     });
     if (res.status === 401 && refreshAccessToken) {
-    return authorizedFetch(await refreshAccessToken(), url, init);
+      token = await refreshAccessToken();
+      continue;
+    }
+    if (isRetryableStatus(res.status) && attempt < MAX_RETRIES - 1) {
+      await sleep(250 * 2 ** attempt + Math.floor(Math.random() * 100));
+      continue;
     }
     return res;
+  }
+  return fetch(url, {
+    ...init,
+    headers: { Authorization: `Bearer ${token}`, ...init.headers },
+  });
 }
 
 async function upsertRemoteEvent(
@@ -182,9 +209,13 @@ type GoogleListItem = {
   extendedProperties?: { private?: Record<string, string> };
 };
 
-function googleItemToRemote(item: GoogleListItem): RemoteSyncedEvent | null {
-  const seqtaKey = item.extendedProperties?.private?.[BSPLUS_GOOGLE_CALENDAR_EVENT_PROP];
-  if (!item.id || !seqtaKey) return null;
+function googleItemToRemote(
+  item: GoogleListItem,
+  includeUnkeyed: boolean,
+): RemoteSyncedEvent | null {
+  if (!item.id) return null;
+  const seqtaKey = item.extendedProperties?.private?.[BSPLUS_GOOGLE_CALENDAR_EVENT_PROP] ?? "";
+  if (!seqtaKey && !includeUnkeyed) return null;
   const startDateTime = item.start?.dateTime ?? (item.start?.date ? `${item.start.date}T00:00:00` : "");
   const endDateTime = item.end?.dateTime ?? (item.end?.date ? `${item.end.date}T00:00:00` : "");
   const timeZone = item.start?.timeZone ?? item.end?.timeZone ?? "UTC";
@@ -208,7 +239,9 @@ export async function listGoogleSyncedEvents(
   calendarId: string,
   range: SyncDateRange,
   refreshAccessToken?: () => Promise<string>,
+  options: ListSyncedEventsOptions = {},
 ): Promise<RemoteSyncedEvent[]> {
+  const includeUnkeyed = options.includeUnkeyed === true;
   const encodedCalendar = encodeURIComponent(calendarId);
   const out: RemoteSyncedEvent[] = [];
   let pageToken: string | undefined;
@@ -241,7 +274,7 @@ export async function listGoogleSyncedEvents(
     }
 
     for (const item of json.items ?? []) {
-      const mapped = googleItemToRemote(item);
+      const mapped = googleItemToRemote(item, includeUnkeyed);
       if (mapped) out.push(mapped);
     }
     pageToken = json.nextPageToken;
@@ -260,13 +293,16 @@ type OutlookListItem = {
   categories?: string[];
 };
 
-function outlookItemToRemote(item: OutlookListItem): RemoteSyncedEvent | null {
+function outlookItemToRemote(
+  item: OutlookListItem,
+  includeUnkeyed: boolean,
+): RemoteSyncedEvent | null {
   if (!item.id) return null;
   const categories = item.categories ?? [];
   if (!categories.includes(BSPLUS_OUTLOOK_CALENDAR_EVENT_CATEGORY)) return null;
   const bodyContent = item.body?.content ?? "";
-  const seqtaKey = parseOutlookSeqtaKey(bodyContent);
-  if (!seqtaKey) return null;
+  const seqtaKey = parseOutlookSeqtaKey(bodyContent) ?? "";
+  if (!seqtaKey && !includeUnkeyed) return null;
 
   const startDateTime = (item.start?.dateTime ?? "").replace(/\.\d+$/, "");
   const endDateTime = (item.end?.dateTime ?? "").replace(/\.\d+$/, "");
@@ -300,7 +336,9 @@ export async function listOutlookSyncedEvents(
   accessToken: string,
   range: SyncDateRange,
   refreshAccessToken?: () => Promise<string>,
+  options: ListSyncedEventsOptions = {},
 ): Promise<RemoteSyncedEvent[]> {
+  const includeUnkeyed = options.includeUnkeyed === true;
   const out: RemoteSyncedEvent[] = [];
   const params = new URLSearchParams({
     startDateTime: toRfc3339Start(range.from),
@@ -332,7 +370,7 @@ export async function listOutlookSyncedEvents(
     }
 
     for (const item of json.value ?? []) {
-      const mapped = outlookItemToRemote(item);
+      const mapped = outlookItemToRemote(item, includeUnkeyed);
       if (mapped) out.push(mapped);
     }
     nextUrl = json["@odata.nextLink"];

src/seqta/utils/calendarSync/syncEngine.ts

@@ -6,33 +6,18 @@ import type { EventMapRecord } from "@/seqta/utils/calendarSync/eventMap";
 import {
   buildDeleteSyncResult,
   buildLessonSyncResult,
+  clearOriginEventMapEntries,
+  collectOriginDeleteEntries,
   deleteTrackedLessonEvents,
   emptyLessonsSyncResult,
   entriesToPrune,
   mergeRemoteEventsIntoMap,
   notConfiguredSyncResult,
   notConnectedSyncResult,
-  originEventMapEntries,
   reconcileRangeForMode,
   reportSyncProgress,
   upsertLessonEvents,
 } from "@/seqta/utils/calendarSync/lessonSyncShared";
-import {
-  googleApiEventBody,
-  mapLessonsToGoogleEvents,
-  outlookGraphEventBody,
-} from "@/seqta/utils/googleCalendar/eventMapper";
-import {
-  readGoogleCalendarState,
-  writeGoogleCalendarState,
-} from "@/seqta/utils/googleCalendar/storage";
-import type {
-  GoogleCalendarDeleteResult,
-  GoogleCalendarEventInput,
-  GoogleCalendarSyncOptions,
-  GoogleCalendarSyncRequest,
-  GoogleCalendarSyncResult,
-} from "@/seqta/utils/googleCalendar/types";
 import {
   deleteGoogleCalendarEvent,
   deleteOutlookCalendarEvent,
@@ -40,14 +25,32 @@ import {
   listOutlookSyncedEvents,
   upsertGoogleCalendarEvent,
   upsertOutlookCalendarEvent,
+  type ListSyncedEventsOptions,
   type RemoteSyncedEvent,
 } from "@/seqta/utils/calendarSync/remoteEvents";
+import {
+  googleApiEventBody,
+  mapLessonsToGoogleEvents,
+  outlookGraphEventBody,
+} from "@/seqta/utils/googleCalendar/eventMapper";
 import { ensureGoogleAppCalendar } from "@/seqta/utils/googleCalendar/calendarProvisioning";
+import {
+  readGoogleCalendarState,
+  writeGoogleCalendarState,
+} from "@/seqta/utils/googleCalendar/storage";
 import {
   syncWindowRange,
   trailingWeekRange,
+  wideCleanupRange,
   type SyncDateRange,
 } from "@/seqta/utils/googleCalendar/syncDateRange";
+import type {
+  GoogleCalendarDeleteResult,
+  GoogleCalendarEventInput,
+  GoogleCalendarSyncOptions,
+  GoogleCalendarSyncRequest,
+  GoogleCalendarSyncResult,
+} from "@/seqta/utils/googleCalendar/types";
 import {
   readOutlookCalendarState,
   writeOutlookCalendarState,
@@ -86,6 +89,7 @@ export type CalendarLessonSyncProvider = {
     accessToken: string,
     range: SyncDateRange,
     refreshAccessToken: () => Promise<string>,
+    options?: ListSyncedEventsOptions,
   ) => Promise<RemoteSyncedEvent[]>;
   toApiBody: (event: GoogleCalendarEventInput) => Record<string, unknown>;
 };
@@ -121,12 +125,13 @@ export const googleLessonSyncProvider: CalendarLessonSyncProvider = {
       body,
       refreshAccessToken,
     ),
-  listSyncedEvents: async (accessToken, range, refreshAccessToken) =>
+  listSyncedEvents: async (accessToken, range, refreshAccessToken, options) =>
     listGoogleSyncedEvents(
       accessToken,
       await getOrProvisionGoogleCalendarId(accessToken),
       range,
       refreshAccessToken,
+      options,
     ),
   toApiBody: googleApiEventBody,
 };
@@ -142,8 +147,8 @@ export const outlookLessonSyncProvider: CalendarLessonSyncProvider = {
     deleteOutlookCalendarEvent(accessToken, eventId, refreshAccessToken),
   upsertEvent: (accessToken, existingId, body, refreshAccessToken) =>
     upsertOutlookCalendarEvent(accessToken, existingId, body, refreshAccessToken),
-  listSyncedEvents: (accessToken, range, refreshAccessToken) =>
-    listOutlookSyncedEvents(accessToken, range, refreshAccessToken),
+  listSyncedEvents: (accessToken, range, refreshAccessToken, options) =>
+    listOutlookSyncedEvents(accessToken, range, refreshAccessToken, options),
   toApiBody: outlookGraphEventBody,
 };
 
@@ -168,10 +173,6 @@ export async function syncLessonsToCalendar(
   const timeZone = Intl.DateTimeFormat().resolvedOptions().timeZone || "UTC";
   const events = mapLessonsToGoogleEvents(request.origin, request.lessons, timeZone);
 
-  if (events.length === 0 && mode === "full") {
-    return emptyLessonsSyncResult();
-  }
-
   reportSyncProgress(options.onProgress, {
     phase: "preparing",
     current: 0,
@@ -204,7 +205,7 @@ export async function syncLessonsToCalendar(
 
   const currentMapKeys = new Set(events.map((event) => eventMapKey(request.origin, event.seqtaKey)));
   const staleEntries = entriesToPrune(eventMap, request.origin, mode, weeksAhead, currentMapKeys);
-  const totalSteps = staleEntries.length + events.length;
+  const totalSteps = Math.max(staleEntries.length + events.length, 1);
   const lastSyncAt = Date.now();
 
   const staleResult = await deleteTrackedLessonEvents(
@@ -220,6 +221,24 @@ export async function syncLessonsToCalendar(
     },
   );
 
+  if (events.length === 0 && mode === "full") {
+    await provider.writeState({
+      eventMap,
+      lastSyncAt,
+      lastSyncOrigin: request.origin,
+    });
+    reportSyncProgress(options.onProgress, {
+      phase: "done",
+      current: totalSteps,
+      total: totalSteps,
+      message: "Sync complete",
+    });
+    if (staleResult.deleted > 0) {
+      return buildLessonSyncResult(0, 0, staleResult.deleted, 0, staleResult.failed, lastSyncAt);
+    }
+    return emptyLessonsSyncResult();
+  }
+
   const upsertResult = await upsertLessonEvents({
     events,
     eventMap,
@@ -282,19 +301,40 @@ export async function deleteSyncedEventsFromCalendar(
     return { success: false, configured: true, connected: false, error: provider.notConnectedError };
   }
 
-  const entries = originEventMapEntries(state.eventMap ?? {}, origin);
-  if (entries.length === 0) {
-    return { success: true, configured: true, connected: true, deleted: 0, failed: 0 };
-  }
-
   reportSyncProgress(options.onProgress, {
     phase: "preparing",
     current: 0,
-    total: entries.length,
+    total: 1,
     message: "Preparing removal…",
   });
 
   const eventMap = { ...(state.eventMap ?? {}) };
+  let accessToken = await getAccessToken();
+  const refreshAccessToken = async () => {
+    accessToken = await getAccessToken();
+    return accessToken;
+  };
+
+  let remoteEvents: RemoteSyncedEvent[] = [];
+  try {
+    remoteEvents = await provider.listSyncedEvents(
+      accessToken,
+      wideCleanupRange(),
+      refreshAccessToken,
+      { includeUnkeyed: true },
+    );
+    mergeRemoteEventsIntoMap(eventMap, origin, remoteEvents, eventMapKey);
+  } catch (err) {
+    verboseLog(`[BetterSEQTA+] ${provider.label} cleanup list failed:`, err);
+  }
+
+  const entries = collectOriginDeleteEntries(eventMap, origin, remoteEvents, eventMapKey);
+  if (entries.length === 0) {
+    clearOriginEventMapEntries(eventMap, origin);
+    await provider.writeState({ eventMap });
+    return { success: true, configured: true, connected: true, deleted: 0, failed: 0 };
+  }
+
   const { deleted, failed } = await deleteTrackedLessonEvents(
     entries,
     eventMap,
@@ -309,6 +349,10 @@ export async function deleteSyncedEventsFromCalendar(
     },
   );
 
+  // Only wipe remaining origin keys when every delete succeeded — keep failed IDs for retry.
+  if (failed === 0) {
+    clearOriginEventMapEntries(eventMap, origin);
+  }
   await provider.writeState({ eventMap });
 
   reportSyncProgress(options.onProgress, {

src/seqta/utils/googleCalendar/syncDateRange.ts

@@ -40,3 +40,13 @@ export function droppedWeekRange(weeksAhead = GOOGLE_CALENDAR_SYNC_WEEKS): SyncD
 export function isDateInRange(date: string, range: SyncDateRange): boolean {
   return date >= range.from && date <= range.until;
 }
+
+/** Wide range used when removing all synced events (covers past + future terms). */
+export function wideCleanupRange(years = 3): SyncDateRange {
+  const now = new Date();
+  const from = new Date(now);
+  from.setFullYear(from.getFullYear() - years);
+  const until = new Date(now);
+  until.setFullYear(until.getFullYear() + years);
+  return { from: toISODate(from), until: toISODate(until) };
+}

src/seqta/utils/googleCalendar/syncEngine.test.ts

@@ -222,6 +222,7 @@ describe("deleteSyncedEventsFromGoogleCalendar", () => {
   it("deletes only events for the requested origin", async () => {
     const result = await deleteSyncedEventsFromGoogleCalendar(ORIGIN, getAccessToken);
 
+    expect(listGoogleSyncedEvents).toHaveBeenCalled();
     expect(deleteGoogleCalendarEvent).toHaveBeenCalledTimes(2);
     expect(result).toMatchObject({
       success: true,
@@ -229,4 +230,31 @@ describe("deleteSyncedEventsFromGoogleCalendar", () => {
       failed: 0,
     });
   });
+
+  it("also deletes remote orphans found by list", async () => {
+    jest.mocked(readGoogleCalendarState).mockResolvedValue({
+      refreshToken: "refresh",
+      calendarId: "app-calendar-id",
+      eventMap: {},
+    });
+    jest.mocked(listGoogleSyncedEvents).mockResolvedValue([
+      {
+        seqtaKey: `${ORIGIN}:cal:1`,
+        id: "remote-a",
+        date: "2026-06-27",
+        fingerprint: "fp",
+      },
+      {
+        seqtaKey: "",
+        id: "orphan-b",
+        date: "2026-06-28",
+        fingerprint: "fp",
+      },
+    ]);
+
+    const result = await deleteSyncedEventsFromGoogleCalendar(ORIGIN, getAccessToken);
+
+    expect(deleteGoogleCalendarEvent).toHaveBeenCalledTimes(2);
+    expect(result).toMatchObject({ success: true, deleted: 2, failed: 0 });
+  });
 });