tweak: update rolling perofrmance

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

@@ -341,13 +341,13 @@
     aria-haspopup="menu"
     aria-expanded={menuOpen}
     aria-busy={isBusy}
-    aria-label={status.connected ? "Google Calendar sync options" : "Connect Google Calendar"}
+    aria-label={status.connected ? "Google Calendar sync options" : "Sync with Calendar"}
     onclick={() => {
       if (!isBusy) toggleMenu();
     }}
   >
     <span class="bsplus-cal-trigger-icon" aria-hidden="true">&#xe9cd;</span>
-    <span class="bsplus-cal-trigger-text">Calendar</span>
+    <span class="bsplus-cal-trigger-text">Sync with Calendar</span>
     {#if status.connected}
       <span class="bsplus-cal-status-dot" aria-hidden="true"></span>
     {/if}
@@ -433,7 +433,7 @@
               />
             </label>
             <p class="bsplus-cal-setting-hint">
-              Keeps a rolling {syncWeeksAhead}-week window. Each week adds the next week and removes the oldest.
+              Syncs {syncWeeksAhead} weeks ahead on connect and manual sync. Weekly auto-sync adds each new week forward.
             </p>
           </div>
         {/if}

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

@@ -97,6 +97,19 @@ describe("syncLessonsToGoogleCalendar", () => {
     });
   });
 
+  it("does not delete events during incremental sync", async () => {
+    const result = await syncLessonsToGoogleCalendar(
+      { origin: ORIGIN, lessons: [baseLesson], mode: "incremental" },
+      getAccessToken,
+    );
+
+    expect(deleteGoogleCalendarEvent).not.toHaveBeenCalled();
+    expect(result).toMatchObject({
+      success: true,
+      deleted: 0,
+    });
+  });
+
   it("reports progress while syncing", async () => {
     const progress: Array<{ phase: string; current: number; total: number }> = [];
     await syncLessonsToGoogleCalendar(

src/seqta/utils/googleCalendar/syncEngine.ts

@@ -7,7 +7,6 @@ import {
   normalizeEventMapEntry,
 } from "@/seqta/utils/googleCalendar/eventMapEntry";
 import {
-  droppedWeekRange,
   isDateInRange,
   syncWindowRange,
 } from "@/seqta/utils/googleCalendar/syncDateRange";
@@ -120,7 +119,6 @@ function entriesToPrune(
   currentMapKeys: Set<string>,
 ): Array<[string, string]> {
   const window = syncWindowRange(weeksAhead);
-  const dropped = droppedWeekRange(weeksAhead);
   const prefix = `${origin}::`;
   const entries: Array<[string, string]> = [];
 
@@ -131,7 +129,7 @@ function entriesToPrune(
 
     let shouldDelete = false;
     if (mode === "incremental") {
-      shouldDelete = !!entry.date && isDateInRange(entry.date, dropped);
+      shouldDelete = false;
     } else if (entry.date) {
       shouldDelete = !isDateInRange(entry.date, window);
     } else {