fix(web): account for Google Calendar's exclusive all-day end-date

A single-day all-day event's End.Date is one calendar day past its own
day (Google Calendar convention, already documented by
TestParseEventTime_AllDayEvent). isMultiDayEvent/multiDayVariant didn't
adjust for this, so every all-day event -- including single-day ones --
was misclassified as multi-day and duplicated across Today and
Tomorrow.

1 files changed, 46 insertions, 0 deletions

diff --git a/internal/handlers/timeline_multiday_test.go b/internal/handlers/timeline_multiday_test.go
index 3dc2005..7af2cbe 100644
--- a/internal/handlers/timeline_multiday_test.go
+++ b/internal/handlers/timeline_multiday_test.go
@@ -81,3 +81,49 @@ func TestMultiDayVariant_DayOutsideSpan_ReturnsEmpty(t *testing.T) {
 		t.Errorf("variant = %q, want empty", got)
 	}
 }
+
+func TestIsMultiDayEvent_SingleDayAllDayEvent_False(t *testing.T) {
+	// Exclusive end-date convention: a single-day all-day event on July 13
+	// has Start=Jul13 00:00, End=Jul14 00:00 (one day past its own day).
+	start, _ := time.Parse(time.RFC3339, "2026-07-13T00:00:00Z")
+	end, _ := time.Parse(time.RFC3339, "2026-07-14T00:00:00Z")
+	item := models.TimelineItem{
+		ID: "allday-1", Type: models.TimelineItemTypeEvent,
+		Time: start, EndTime: &end, IsAllDay: true,
+	}
+	if isMultiDayEvent(item) {
+		t.Error("expected a single-day all-day event (exclusive end-date) to not be multi-day")
+	}
+}
+
+func TestIsMultiDayEvent_MultiDayAllDayEvent_True(t *testing.T) {
+	// A 3-day all-day event (Jul 13, 14, 15) has End=Jul16 00:00 (exclusive).
+	start, _ := time.Parse(time.RFC3339, "2026-07-13T00:00:00Z")
+	end, _ := time.Parse(time.RFC3339, "2026-07-16T00:00:00Z")
+	item := models.TimelineItem{
+		ID: "allday-2", Type: models.TimelineItemTypeEvent,
+		Time: start, EndTime: &end, IsAllDay: true,
+	}
+	if !isMultiDayEvent(item) {
+		t.Error("expected a 3-day all-day event to be multi-day")
+	}
+}
+
+func TestMultiDayVariant_MultiDayAllDayEvent_LastRealDayIsEnds(t *testing.T) {
+	// The 3-day all-day event above (Jul 13-15 inclusive, End=Jul16 exclusive)
+	// must report "ends" on Jul 15 (its real last day), not Jul 16.
+	start, _ := time.Parse(time.RFC3339, "2026-07-13T00:00:00Z")
+	end, _ := time.Parse(time.RFC3339, "2026-07-16T00:00:00Z")
+	item := models.TimelineItem{
+		ID: "allday-2", Type: models.TimelineItemTypeEvent,
+		Time: start, EndTime: &end, IsAllDay: true,
+	}
+	renderDay, _ := time.Parse(time.RFC3339, "2026-07-15T00:00:00Z")
+	if got := multiDayVariant(item, renderDay); got != "ends" {
+		t.Errorf("variant on last real day = %q, want %q", got, "ends")
+	}
+	exclusiveEndDay, _ := time.Parse(time.RFC3339, "2026-07-16T00:00:00Z")
+	if got := multiDayVariant(item, exclusiveEndDay); got != "" {
+		t.Errorf("variant on the exclusive (non-real) end day = %q, want empty", got)
+	}
+}