calendar: enforce two-phase zoom-in morph before view switch

frontend/app.vue

@@ -2281,6 +2281,7 @@ type CalendarZoomGhost = {
 };
 
 const calendarContentWrapRef = ref<HTMLElement | null>(null);
+const calendarZoomOverlayRef = ref<HTMLElement | null>(null);
 const calendarHoveredMonthIndex = ref<number | null>(null);
 const calendarHoveredWeekStartKey = ref("");
 const calendarHoveredDayKey = ref("");
@@ -2400,13 +2401,29 @@ function getElementRectInCalendar(element: HTMLElement | null): CalendarRect | n
   const wrapRect = calendarContentWrapRef.value?.getBoundingClientRect();
   if (!wrapRect) return null;
   const rect = element.getBoundingClientRect();
-  const left = Math.max(0, rect.left - wrapRect.left);
-  const top = Math.max(0, rect.top - wrapRect.top);
-  const width = Math.max(24, Math.min(rect.width, wrapRect.width - left));
-  const height = Math.max(24, Math.min(rect.height, wrapRect.height - top));
+  const left = Math.max(0, Math.min(rect.left - wrapRect.left, wrapRect.width));
+  const top = Math.max(0, Math.min(rect.top - wrapRect.top, wrapRect.height));
+  const right = Math.max(0, Math.min(rect.right - wrapRect.left, wrapRect.width));
+  const bottom = Math.max(0, Math.min(rect.bottom - wrapRect.top, wrapRect.height));
+  const visibleWidth = right - left;
+  const visibleHeight = bottom - top;
+  if (visibleWidth < 2 || visibleHeight < 2) return null;
+  const width = Math.min(Math.max(24, visibleWidth), wrapRect.width - left);
+  const height = Math.min(Math.max(24, visibleHeight), wrapRect.height - top);
   return { left, top, width, height };
 }
 
+function fallbackZoomOriginRect(viewportRect: CalendarRect): CalendarRect {
+  const width = Math.max(96, Math.round(viewportRect.width * 0.28));
+  const height = Math.max(64, Math.round(viewportRect.height * 0.24));
+  return {
+    left: Math.max(0, Math.round((viewportRect.width - width) / 2)),
+    top: Math.max(0, Math.round((viewportRect.height - height) / 2)),
+    width: Math.min(width, viewportRect.width),
+    height: Math.min(height, viewportRect.height),
+  };
+}
+
 function weekRowStartForDate(key: string) {
   const date = new Date(`${key}T00:00:00`);
   date.setDate(date.getDate() - date.getDay());
@@ -2490,30 +2507,61 @@ function primeCalendarRect(rect: CalendarRect) {
 }
 
 function morphCalendarRect(toRect: CalendarRect) {
-  requestAnimationFrame(() => {
-    calendarZoomOverlay.value = {
-      active: true,
-      left: toRect.left,
-      top: toRect.top,
-      width: toRect.width,
-      height: toRect.height,
-    };
+  calendarZoomOverlay.value = {
+    active: true,
+    left: toRect.left,
+    top: toRect.top,
+    width: toRect.width,
+    height: toRect.height,
+  };
+}
+
+function nextAnimationFrame() {
+  return new Promise<void>((resolve) => {
+    requestAnimationFrame(() => resolve());
   });
 }
 
-function waitCalendarZoom() {
+async function flushCalendarZoomStartFrame() {
+  await nextTick();
+  await nextAnimationFrame();
+  calendarZoomOverlayRef.value?.getBoundingClientRect();
+  await nextAnimationFrame();
+}
+
+function waitCalendarZoomTransition() {
+  const overlay = calendarZoomOverlayRef.value;
+  if (!overlay) {
+    return new Promise<void>((resolve) => {
+      setTimeout(() => resolve(), CALENDAR_ZOOM_DURATION_MS);
+    });
+  }
   return new Promise<void>((resolve) => {
-    setTimeout(() => resolve(), CALENDAR_ZOOM_DURATION_MS);
+    let settled = false;
+    const finish = () => {
+      if (settled) return;
+      settled = true;
+      overlay.removeEventListener("transitionend", onTransitionEnd);
+      clearTimeout(fallbackTimer);
+      resolve();
+    };
+    const onTransitionEnd = (event: TransitionEvent) => {
+      if (event.target !== overlay) return;
+      if (!["left", "top", "width", "height"].includes(event.propertyName)) return;
+      finish();
+    };
+    const fallbackTimer = setTimeout(() => finish(), CALENDAR_ZOOM_DURATION_MS + 140);
+    overlay.addEventListener("transitionend", onTransitionEnd);
   });
 }
 
 async function animateCalendarZoomIn(sourceElement: HTMLElement | null, ghost: CalendarZoomGhost, apply: () => void) {
-  const fromRect = getElementRectInCalendar(sourceElement);
   const viewportRect = getCalendarViewportRect();
-  if (!fromRect || !viewportRect) {
+  if (!viewportRect) {
     apply();
     return;
   }
+  const fromRect = getElementRectInCalendar(sourceElement) ?? fallbackZoomOriginRect(viewportRect);
 
   clearCalendarZoomPrime();
   calendarZoomBusy.value = true;
@@ -2521,9 +2569,9 @@ async function animateCalendarZoomIn(sourceElement: HTMLElement | null, ghost: C
     primeCalendarRect(fromRect);
     calendarZoomGhost.value = ghost;
     calendarSceneMasked.value = true;
-    await nextTick();
+    await flushCalendarZoomStartFrame();
     morphCalendarRect(viewportRect);
-    await waitCalendarZoom();
+    await waitCalendarZoomTransition();
     apply();
     await nextTick();
   } finally {
@@ -2546,7 +2594,7 @@ async function animateCalendarZoomOut(apply: () => void, resolveTarget: () => HT
     primeCalendarRect(viewportRect);
     calendarZoomGhost.value = zoomGhostForCurrentView();
     calendarSceneMasked.value = true;
-    await nextTick();
+    await flushCalendarZoomStartFrame();
     apply();
     await nextTick();
     const targetRect = getElementRectInCalendar(resolveTarget());
@@ -2558,7 +2606,7 @@ async function animateCalendarZoomOut(apply: () => void, resolveTarget: () => HT
       return;
     }
     morphCalendarRect(targetRect);
-    await waitCalendarZoom();
+    await waitCalendarZoomTransition();
   } finally {
     clearCalendarZoomOverlay();
     calendarSceneMasked.value = false;
@@ -4964,6 +5012,7 @@ async function decideFeedCard(card: FeedCard, decision: "accepted" | "rejected")
 		            </div>
               <div
                 v-if="calendarZoomOverlay.active"
+                ref="calendarZoomOverlayRef"
                 class="calendar-zoom-overlay"
                 :style="calendarZoomOverlayStyle"
               >