fix(detail): clamp a backwards DTEND instead of dropping the event (#34)

toEventDetailCore returned null when a present DTEND preceded DTSTART, the
only remaining false-drop that surfaces as the generic "Something went
wrong." error screen — the same un-openable trap as the pre-1970 DTSTART
bug, and worse because the user can't even open the malformed event to fix
it. Clamp the end to DTSTART (a zero-length event) instead, matching how
SearchMapper already coerces its end. After this the detail mapper drops a
row only when DTSTART is genuinely absent (unrenderable).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapper.kt

@@ -37,16 +37,15 @@ internal fun ColumnReader.toEventDetailCore(
     // Recurring events store DURATION instead of DTEND, so the series row's
     // DTEND is null. Keep the event (end == begin); callers that opened a
     // specific occurrence supply the real per-occurrence times from
-    // CalendarContract.Instances. Only a present-but-backwards DTEND is malformed.
+    // CalendarContract.Instances. A present-but-backwards DTEND is malformed,
+    // but dropping the row would make the event un-openable — the same trap as
+    // the pre-1970 DTSTART bug above (issue #34): it would surface as the
+    // generic error screen with no way to open the event and fix it. Clamp to a
+    // zero-length event instead (matching SearchMapper's coerceAtLeast).
     val end = if (isNull(EventDetailProjection.IDX_DTEND)) {
         begin
     } else {
-        val rawEnd = getLong(EventDetailProjection.IDX_DTEND)
-        if (rawEnd < begin) {
-            Log.w(TAG, "Dropping event with dtend=$rawEnd < dtstart=$begin")
-            return null
-        }
-        rawEnd
+        getLong(EventDetailProjection.IDX_DTEND).coerceAtLeast(begin)
     }
 
     // Kept raw (no untitled fallback): the detail screen substitutes its own

app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapperTest.kt

@@ -120,9 +120,14 @@ class EventDetailMapperTest {
     }
 
     @Test
-    fun `dtend before dtstart drops detail`() {
+    fun `dtend before dtstart is clamped to a zero-length event, not dropped`() {
+        // A backwards DTEND is malformed, but dropping it would make the event
+        // un-openable (the "Something went wrong" trap, same as issue #34); keep
+        // it as a zero-length event so the user can still open and fix it.
         val detail = detailReader(dtstart = 2000L, dtend = 1000L).toDetail()
-        assertThat(detail).isNull()
+        assertThat(detail).isNotNull()
+        assertThat(detail!!.instance.start.toEpochMilliseconds()).isEqualTo(2000L)
+        assertThat(detail.instance.end.toEpochMilliseconds()).isEqualTo(2000L)
     }
 
     @Test