fix: move EXDATE with the series when its times change (#248)

Dropping a single occurrence on a calendar with no _sync_id records it in
the master row's EXDATE (the #47 fix; synced calendars use a cancelled
exception instead and are unaffected). An EXDATE stamp is an absolute
instant — it excludes an occurrence only while the series keeps generating
one at exactly that instant — and nothing ever rewrote it when the anchor
moved.

buildEventUpdateValues shifts DTSTART on any time change and rewrites
RRULE/DURATION/zone/all-day, so every occurrence regenerates elsewhere
while the stamps stay behind matching nothing: the occurrence the user
deleted comes back. updateEventFromOccurrence is worse — it splits the
series by inserting a fresh event built from the form, which carries no
EXDATE at all, so every exclusion in the tail is lost.

Shift each stamp by the same wall-clock delta the anchor takes, re-resolved
in the event's (possibly new) zone. Reusing the anchor's rule is what keeps
an exclusion pinned to its occurrence when a DST boundary sits between the
two, or the zone itself changed; a millisecond delta would bake in the
offset that happened to apply at the edited occurrence. Parsing reads
all-day-ness from the old form and writing takes it from the new one, so
the VALUE=DATE and date-time forms convert into each other when the event
switches — the wrong form matches no occurrence and loses the exclusion
just as surely as the wrong instant.

Stamps in a shape Calendula never writes (a TZID-parameterised or floating
one from a sync adapter) are left exactly as they are, whole list included:
a stale stamp excludes nothing, but a mangled one could exclude the wrong
occurrence.

For the split, the parent's stamps past the cutoff are re-timed onto the
new series. The one *at* the split point is dropped: it names the
occurrence being edited, which exists by definition, and honouring a stale
exclusion for it would swallow the edit whole. The parent keeps its full
list — stamps past the truncation are inert once it stops generating those
occurrences. The write repeats the whole time/recurrence set for the reason
#47 documents (an EXDATE-only update is not read as a recurrence change),
and a failure rolls the new series back before the parent is truncated, so
the split fails whole rather than landing with the exclusions dropped.

Dropping the recurrence now clears EXDATE with the RRULE. Dormant rather
than harmless: adding a recurrence back later would punch the old holes
into the new one.

This reaches every calendar type through the "all events" path, including
synced ones, where an upstream EXDATE must move with the series for the
same reason — and reaches a calendar move too, which copies EXDATE verbatim
and then applies the field edits as a normal series update.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- **A deleted occurrence no longer comes back when the series is re-timed.**
+  Delete a single occurrence of a repeating event, then change the time of the
+  whole series, and the occurrence you had removed reappeared. Doing it the
+  other way round — "This and all following events" — lost every removal in the
+  part of the series being changed. Removals now travel with the event: they
+  keep their place in the series across a time change, a move to a different
+  day, a timezone change and a switch to or from an all-day event, and they
+  carry over when a series is split. Repeating events on your device's own
+  calendars are affected, including the birthday and anniversary calendars
+  Calendula creates from your contacts ([#248]).
+
 ## [2.19.3] — 2026-08-22
 
 ### Added
@@ -1471,3 +1483,4 @@ automatically, with zero telemetry and no internet permission.
 [#192]: https://codeberg.org/jlmakiola/calendula/issues/192
 [#196]: https://codeberg.org/jlmakiola/calendula/issues/196
 [#214]: https://codeberg.org/jlmakiola/calendula/issues/214
+[#248]: https://codeberg.org/jlmakiola/calendula/issues/248

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

@@ -976,10 +976,12 @@ class AndroidCalendarDataSource @Inject constructor(
         updated: EventForm,
         allDayReminderTimeMinutes: Int,
     ) {
+        val row = querySeriesRow(eventId)
         val values = buildEventUpdateValues(
             original = original,
             updated = updated,
-            seriesDtStartMillis = querySeriesRow(eventId).dtStartMillis,
+            seriesDtStartMillis = row.dtStartMillis,
+            seriesExdate = row.exdate,
             zone = ZoneId.systemDefault(),
         )
         if (values.isNotEmpty()) {
@@ -1228,10 +1230,66 @@ class AndroidCalendarDataSource @Inject constructor(
         }
         // Insert the new series first: if it fails, the original is untouched.
         val newEventId = insertEvent(updated, allDayReminderTimeMinutes)
+        carrySplitExdate(newEventId, row, beginMillis, original, updated)
         truncateSeries(eventId, row, beginMillis)
         return newEventId
     }
 
+    /**
+     * Carry the [parent]'s exclusions for occurrences past [beginMillis] onto the
+     * series [newEventId] that now owns them, re-timed by the shift the split
+     * applied ([shiftedExdate]/[exdateAfter]). [insertEvent] builds the new row
+     * from the form, which knows nothing about them, so without this every
+     * occurrence the user had deleted from the tail of the series comes back.
+     *
+     * The whole time/recurrence set rides along with EXDATE for the reason
+     * [buildOccurrenceExdateValues] documents: on its own the provider does not
+     * read an EXDATE write as a recurrence change, and leaves the instances it
+     * expanded on insert standing.
+     *
+     * A failure rolls the new series back and throws, so the split fails whole
+     * rather than landing with the exclusions quietly dropped — the parent is
+     * still untruncated at this point, so the event is left exactly as it was.
+     */
+    private fun carrySplitExdate(
+        newEventId: Long,
+        parent: SeriesRow,
+        beginMillis: Long,
+        original: EventForm,
+        updated: EventForm,
+    ) {
+        // Dropping the recurrence in the same save leaves a one-off tail, and an
+        // exclusion means nothing on a row that doesn't recur.
+        if (updated.rrule.isNullOrBlank()) return
+        val carried = shiftedExdate(
+            existingExdate = exdateAfter(parent.exdate, beginMillis, original.isAllDay),
+            original = original,
+            updated = updated,
+            zone = ZoneId.systemDefault(),
+        ) ?: return
+        val row = querySeriesRow(newEventId)
+        val values = ContentValues().apply {
+            put(CalendarContract.Events.EXDATE, carried)
+            put(CalendarContract.Events.DTSTART, row.dtStartMillis)
+            put(CalendarContract.Events.RRULE, row.rrule)
+            put(CalendarContract.Events.DURATION, row.duration)
+            put(CalendarContract.Events.EVENT_TIMEZONE, row.timezone)
+            put(CalendarContract.Events.ALL_DAY, row.allDay)
+        }
+        try {
+            val rows = resolver.update(
+                ContentUris.withAppendedId(CalendarContract.Events.CONTENT_URI, newEventId),
+                values, null, null,
+            )
+            if (rows == 0) {
+                throw WriteFailedException("carry exdate onto split series id=$newEventId")
+            }
+        } catch (t: Throwable) {
+            runCatching { deleteEvent(newEventId) }
+            throw t
+        }
+    }
+
     override fun deleteEventFromOccurrence(eventId: Long, beginMillis: Long) {
         val row = querySeriesRow(eventId)
         // From the first occurrence on = the whole series; also the fallback

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

@@ -10,6 +10,9 @@ import java.time.Duration
 import java.time.Instant
 import java.time.ZoneId
 import java.time.ZoneOffset
+import java.time.format.DateTimeFormatter
+import java.time.format.ResolverStyle
+import java.time.LocalDate as JavaLocalDate
 import java.time.LocalDateTime as JavaLocalDateTime
 
 /** Provider-ready DTSTART / DTEND / EVENT_TIMEZONE for an event write. */
@@ -134,18 +137,21 @@ internal fun buildEventInsertValues(
  *
  * Time fields travel together (the provider validates them as a unit):
  * - unchanged times, all-day flag and rrule → no time columns at all;
- * - non-recurring result → DTSTART/DTEND, DURATION and RRULE cleared;
+ * - non-recurring result → DTSTART/DTEND, DURATION, RRULE and EXDATE cleared;
  * - recurring result → the *series* DTSTART moves by the same **wall-clock**
  *   shift the user applied to the displayed occurrence and is re-resolved in the
  *   event's zone ([seriesDtStartMillis] is the row's current DTSTART), DURATION
- *   replaces DTEND, RRULE is written. This keeps past occurrences intact when
+ *   replaces DTEND, RRULE is written, and the row's exclusions
- *   someone edits a later occurrence's time, and keeps the anchor's time-of-day
+ *   ([seriesExdate], the current EXDATE) travel with the anchor. This keeps past
- *   stable across a DST boundary or a zone change between the two.
+ *   occurrences intact when someone edits a later occurrence's time, and keeps
+ *   the anchor's time-of-day stable across a DST boundary or a zone change
+ *   between the two.
  */
 internal fun buildEventUpdateValues(
     original: EventForm,
     updated: EventForm,
     seriesDtStartMillis: Long,
+    seriesExdate: String?,
     zone: ZoneId,
 ): Map<String, Any?> = buildMap {
     if (updated.title.trim() != original.title.trim()) {
@@ -185,6 +191,10 @@ internal fun buildEventUpdateValues(
         put(CalendarContract.Events.DTEND, newTimes.dtEndMillis)
         put(CalendarContract.Events.RRULE, null)
         put(CalendarContract.Events.DURATION, null)
+        // The exclusions named occurrences of a series that no longer exists.
+        // Left behind they are dormant rather than harmless: adding a recurrence
+        // back later would punch the old holes into the new one.
+        put(CalendarContract.Events.EXDATE, null)
     } else {
         // Move the series anchor by the *wall-clock* shift the user applied to the
         // displayed occurrence, then re-resolve it in the event's (possibly new)
@@ -206,6 +216,14 @@ internal fun buildEventUpdateValues(
         put(CalendarContract.Events.DTEND, null)
         put(CalendarContract.Events.RRULE, updated.rrule)
         put(CalendarContract.Events.DURATION, newTimes.toRfc2445Duration(updated.isAllDay))
+        // An EXDATE stamp is an absolute instant, so it excludes an occurrence
+        // only while the series keeps generating one at exactly that instant. The
+        // anchor has just moved, so every occurrence regenerates elsewhere and a
+        // stamp left behind matches none of them — the occurrence the user deleted
+        // comes back. Move the stamps the same way the anchor moved.
+        shiftedExdate(seriesExdate, original, updated, zone)
+            ?.takeIf { it != seriesExdate }
+            ?.let { put(CalendarContract.Events.EXDATE, it) }
     }
 }
 
@@ -420,11 +438,7 @@ internal fun buildOccurrenceExdateValues(
     allDay: Int,
 ): Map<String, Any?> {
     val stamp = formatExdateStamp(occurrenceMillis, isAllDay = allDay != 0)
-    val existing = existingExdate?.split(',')
+    val merged = (exdateStamps(existingExdate) + stamp).distinct().joinToString(",")
-        ?.map { it.trim() }
-        ?.filter { it.isNotEmpty() }
-        .orEmpty()
-    val merged = (existing + stamp).distinct().joinToString(",")
     return mapOf(
         CalendarContract.Events.EXDATE to merged,
         CalendarContract.Events.DTSTART to dtStartMillis,
@@ -435,22 +449,122 @@ internal fun buildOccurrenceExdateValues(
     )
 }
 
+/**
+ * [existingExdate] with every stamp re-timed by the same **wall-clock** shift the
+ * series anchor takes from [original] to [updated] — the exclusions' half of the
+ * anchor move [buildEventUpdateValues] performs, and what carries them onto the
+ * new series when "this and following" splits one.
+ *
+ * A stamp is an absolute instant, so it keeps naming its occurrence only if it
+ * moves exactly as the occurrence does: shifted in wall clock and re-resolved in
+ * the event's (possibly new) zone. A millisecond delta would instead bake in the
+ * offset that happened to apply at the edited occurrence — an hour off for any
+ * exclusion on the far side of a DST boundary. All-day-ness is read from
+ * [original] and written from [updated], so the `VALUE=DATE` and date-time forms
+ * convert into each other when the event switches.
+ *
+ * Null when there is nothing to carry: no stamps, or a stamp in a form Calendula
+ * never writes (a `TZID=`-parameterised or floating one from a sync adapter). Those
+ * are left exactly as they are rather than guessed at — a stale stamp excludes
+ * nothing, but a mangled one could exclude the wrong occurrence.
+ */
+internal fun shiftedExdate(
+    existingExdate: String?,
+    original: EventForm,
+    updated: EventForm,
+    zone: ZoneId,
+): String? {
+    val stamps = exdateStamps(existingExdate)
+    if (stamps.isEmpty()) return null
+    val fromZone = original.writeZone(zone)
+    val toZone = updated.writeZone(zone)
+    val wallClockShift = Duration.between(original.anchorLocal(), updated.anchorLocal())
+    return stamps
+        .map { stamp ->
+            val local = parseExdateStamp(stamp, original.isAllDay, fromZone) ?: return null
+            formatExdateStamp(local.plus(wallClockShift), updated.isAllDay, toZone)
+        }
+        .distinct()
+        .joinToString(",")
+}
+
+/**
+ * The stamps of [existingExdate] naming occurrences after [beginMillis] — the ones
+ * that belong to the *new* series once "this and following" splits a recurring
+ * event there. The parent keeps the full list; its stamps past the split point are
+ * simply inert once it stops generating those occurrences.
+ *
+ * The occurrence at [beginMillis] itself is never carried. It is the one the user
+ * is editing, so it exists by definition, and honouring a stale exclusion for it
+ * would swallow the edit whole.
+ *
+ * Null when nothing qualifies, or when a stamp can't be read (see [shiftedExdate]).
+ */
+internal fun exdateAfter(existingExdate: String?, beginMillis: Long, isAllDay: Boolean): String? {
+    val stamps = exdateStamps(existingExdate)
+    if (stamps.isEmpty()) return null
+    return stamps
+        .filter { stamp ->
+            val utc = parseExdateStamp(stamp, isAllDay, ZoneOffset.UTC) ?: return null
+            utc.toInstant(ZoneOffset.UTC).toEpochMilli() > beginMillis
+        }
+        .takeIf { it.isNotEmpty() }
+        ?.joinToString(",")
+}
+
+/** The individual stamps of an EXDATE column value; it is a comma-separated list. */
+private fun exdateStamps(exdate: String?): List<String> = exdate
+    ?.split(',')
+    ?.map { it.trim() }
+    ?.filter { it.isNotEmpty() }
+    .orEmpty()
+
 /**
  * One EXDATE entry for the occurrence starting at [occurrenceMillis]. Both forms
  * are UTC: the provider stores an all-day DTSTART at UTC midnight, so its date
  * reads off the UTC calendar day.
  */
-private fun formatExdateStamp(occurrenceMillis: Long, isAllDay: Boolean): String {
+private fun formatExdateStamp(occurrenceMillis: Long, isAllDay: Boolean): String =
-    val utc = Instant.ofEpochMilli(occurrenceMillis).atZone(ZoneOffset.UTC)
+    formatExdateStamp(
-    return if (isAllDay) {
+        local = Instant.ofEpochMilli(occurrenceMillis).atZone(ZoneOffset.UTC).toLocalDateTime(),
-        "%04d%02d%02d".format(utc.year, utc.monthValue, utc.dayOfMonth)
+        isAllDay = isAllDay,
-    } else {
+        zone = ZoneOffset.UTC,
-        "%04d%02d%02dT%02d%02d%02dZ".format(
-            utc.year, utc.monthValue, utc.dayOfMonth,
-            utc.hour, utc.minute, utc.second,
     )
+
+/**
+ * One EXDATE entry for the occurrence whose wall clock in [zone] is [local]. An
+ * all-day entry keeps only the date (its time-of-day is the anchor's, not the
+ * occurrence's); a timed one is resolved in [zone] and written as a UTC instant.
+ */
+private fun formatExdateStamp(local: JavaLocalDateTime, isAllDay: Boolean, zone: ZoneId): String =
+    if (isAllDay) {
+        local.toLocalDate().format(ALL_DAY_EXDATE)
+    } else {
+        local.atZone(zone).withZoneSameInstant(ZoneOffset.UTC).format(TIMED_EXDATE)
     }
-}
+
+/**
+ * [stamp] as the wall clock it names in [zone] — the inverse of
+ * [formatExdateStamp]. Null for anything but the two forms Calendula writes, so a
+ * caller can tell "not ours, leave it alone" from a value it may safely re-time.
+ */
+private fun parseExdateStamp(stamp: String, isAllDay: Boolean, zone: ZoneId): JavaLocalDateTime? =
+    runCatching {
+        if (isAllDay) {
+            JavaLocalDate.parse(stamp, ALL_DAY_EXDATE).atStartOfDay()
+        } else {
+            JavaLocalDateTime.parse(stamp, TIMED_EXDATE)
+                .atZone(ZoneOffset.UTC).withZoneSameInstant(zone).toLocalDateTime()
+        }
+    }.getOrNull()
+
+/** `VALUE=DATE` EXDATE form, for an all-day series. */
+private val ALL_DAY_EXDATE: DateTimeFormatter =
+    DateTimeFormatter.ofPattern("uuuuMMdd").withResolverStyle(ResolverStyle.STRICT)
+
+/** UTC date-time EXDATE form, for a timed series. */
+private val TIMED_EXDATE: DateTimeFormatter =
+    DateTimeFormatter.ofPattern("uuuuMMdd'T'HHmmss'Z'").withResolverStyle(ResolverStyle.STRICT)
 
 /**
  * The `EVENT_COLOR` / `EVENT_COLOR_KEY` columns for a colour selection. A

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

@@ -128,7 +128,8 @@ class EventWriteMapperTest {
         original: EventForm,
         updated: EventForm,
         series: Long = seriesStart,
-    ): Map<String, Any?> = buildEventUpdateValues(original, updated, series, berlin)
+        exdate: String? = null,
+    ): Map<String, Any?> = buildEventUpdateValues(original, updated, series, exdate, berlin)
 
     /** The instant [local] names in [zoneId], as the provider would store it. */
     private fun instantAt(local: String, zoneId: String): Long =
@@ -558,6 +559,239 @@ class EventWriteMapperTest {
         assertThat(values[CalendarContract.Events.ALL_DAY]).isEqualTo(1)
     }
 
+    // --- EXDATE follows the series when its times change (Codeberg #248) ---
+
+    /** A weekly series whose displayed occurrence runs 15 July 2026, 09:00–10:00. */
+    private fun julySeries(): EventForm = form(
+        start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(9, 0)),
+        end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(10, 0)),
+    ).copy(rrule = "FREQ=WEEKLY")
+
+    /** [julySeries] pushed to [hour]:00, the shift an "all events" time edit makes. */
+    private fun EventForm.atHour(hour: Int): EventForm = copy(
+        start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(hour, 0)),
+        end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(hour + 1, 0)),
+    )
+
+    @Test
+    fun `a series time edit moves its exclusions with the anchor`() {
+        // The bug: the stamp stayed at the old instant, which the moved series no
+        // longer generates, so the occurrence the user deleted came back.
+        val series = instantAt("2026-07-01T09:00", "Europe/Berlin")
+        val original = julySeries()
+        // 8 July 09:00 Berlin (CEST, +2) == 07:00Z; at 10:00 it must read 08:00Z.
+        val values = update(original, original.atHour(10), series, "20260708T070000Z")
+        assertThat(values[CalendarContract.Events.EXDATE]).isEqualTo("20260708T080000Z")
+    }
+
+    @Test
+    fun `an exclusion keeps its wall clock across a DST boundary`() {
+        // Anchor and edited occurrence are in July (CEST, +2); the excluded
+        // occurrence sits in January (CET, +1). Shifting by the millisecond delta
+        // measured at the edited occurrence would leave it an hour off.
+        val series = instantAt("2026-01-07T09:00", "Europe/Berlin")
+        val original = julySeries()
+        // 14 January 09:00 Berlin == 08:00Z; at 10:00 it must read 09:00Z.
+        val values = update(original, original.atHour(10), series, "20260114T080000Z")
+        assertThat(values[CalendarContract.Events.EXDATE]).isEqualTo("20260114T090000Z")
+    }
+
+    @Test
+    fun `pinning a series to another zone re-resolves its exclusions there`() {
+        val series = instantAt("2026-07-01T09:00", "Europe/Berlin")
+        val original = julySeries()
+        val values = update(
+            original,
+            original.copy(timezone = "Asia/Tokyo"),
+            series,
+            "20260716T070000Z",
+        )
+        // The exclusion still reads 09:00 — now 09:00 in Tokyo (+9) == 00:00Z.
+        assertThat(values[CalendarContract.Events.EXDATE]).isEqualTo("20260716T000000Z")
+    }
+
+    @Test
+    fun `an all-day series move shifts its exclusions by whole days`() {
+        val series = instantAt("2026-07-01T00:00", "UTC")
+        val original = form(
+            isAllDay = true,
+            start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(0, 0)),
+            end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(0, 0)),
+        ).copy(rrule = "FREQ=WEEKLY")
+        val moved = original.copy(
+            start = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(0, 0)),
+            end = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(0, 0)),
+        )
+
+        assertThat(update(original, moved, series, "20260722")[CalendarContract.Events.EXDATE])
+            .isEqualTo("20260724")
+    }
+
+    @Test
+    fun `switching a series to all-day rewrites its exclusions as dates`() {
+        // The two forms aren't interchangeable: a date-time stamp on an all-day
+        // series matches no occurrence, so the exclusion would be lost.
+        val series = instantAt("2026-07-01T09:00", "Europe/Berlin")
+        val original = julySeries()
+        val values = update(original, original.copy(isAllDay = true), series, "20260722T070000Z")
+        assertThat(values[CalendarContract.Events.EXDATE]).isEqualTo("20260722")
+    }
+
+    @Test
+    fun `switching a series back to timed rewrites its exclusions as instants`() {
+        val series = instantAt("2026-07-01T00:00", "UTC")
+        val original = form(
+            isAllDay = true,
+            start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(0, 0)),
+            end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(0, 0)),
+        ).copy(rrule = "FREQ=WEEKLY")
+        val timed = original.copy(
+            isAllDay = false,
+            start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(9, 0)),
+            end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(10, 0)),
+        )
+        // The excluded day gains the new 09:00 Berlin time-of-day == 07:00Z.
+        assertThat(update(original, timed, series, "20260722")[CalendarContract.Events.EXDATE])
+            .isEqualTo("20260722T070000Z")
+    }
+
+    @Test
+    fun `a text-only edit leaves the exclusions alone`() {
+        val original = julySeries()
+        val values = update(original, original.copy(title = "Renamed"), exdate = "20260722T070000Z")
+        assertThat(values).doesNotContainKey(CalendarContract.Events.EXDATE)
+    }
+
+    @Test
+    fun `changing only the rule rewrites no exclusions`() {
+        // The times are untouched, so every surviving occurrence keeps its instant
+        // and the stamps still name the right ones.
+        val original = julySeries()
+        val values = update(original, original.copy(rrule = "FREQ=DAILY"), exdate = "20260722T070000Z")
+        assertThat(values[CalendarContract.Events.RRULE]).isEqualTo("FREQ=DAILY")
+        assertThat(values).doesNotContainKey(CalendarContract.Events.EXDATE)
+    }
+
+    @Test
+    fun `an exdate form we do not write is left untouched`() {
+        // A sync adapter may store a TZID-parameterised or floating stamp. A stale
+        // stamp excludes nothing; a mangled one could exclude the wrong occurrence.
+        val original = julySeries()
+        val values = update(
+            original,
+            original.atHour(10),
+            instantAt("2026-07-01T09:00", "Europe/Berlin"),
+            "TZID=Europe/Berlin;20260722T090000",
+        )
+        assertThat(values).doesNotContainKey(CalendarContract.Events.EXDATE)
+    }
+
+    @Test
+    fun `removing the recurrence clears the exclusions with it`() {
+        // Dormant, not harmless: adding a recurrence back later would punch the old
+        // holes into the new one.
+        val original = julySeries()
+        val values = update(original, original.copy(rrule = null), exdate = "20260722T070000Z")
+        assertThat(values).containsEntry(CalendarContract.Events.EXDATE, null)
+    }
+
+    @Test
+    fun `undoing a series move lands the exclusions back where they started`() {
+        val series = instantAt("2026-01-07T09:00", "Europe/Berlin")
+        val original = julySeries()
+        val moved = original.copy(
+            start = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(14, 30)),
+            end = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(15, 30)),
+        )
+        val exdate = "20260722T070000Z"
+
+        val forward = update(original, moved, series, exdate)
+        val movedExdate = forward[CalendarContract.Events.EXDATE] as String
+        assertThat(movedExdate).isNotEqualTo(exdate)
+
+        val back = update(
+            moved,
+            original,
+            forward[CalendarContract.Events.DTSTART] as Long,
+            movedExdate,
+        )
+        assertThat(back[CalendarContract.Events.EXDATE]).isEqualTo(exdate)
+    }
+
+    @Test
+    fun `a series with no exclusions writes no exdate column`() {
+        val series = instantAt("2026-07-01T09:00", "Europe/Berlin")
+        val original = julySeries()
+        assertThat(update(original, original.atHour(10), series, exdate = null))
+            .doesNotContainKey(CalendarContract.Events.EXDATE)
+    }
+
+    // --- exdateAfter (the exclusions a "this and following" split inherits) ---
+
+    @Test
+    fun `a split carries only the exclusions past the split point`() {
+        // The occurrence at the split point is the one being edited, so it exists
+        // by definition — a stale exclusion for it would swallow the edit whole.
+        assertThat(
+            exdateAfter(
+                existingExdate = "20260708T080000Z,20260715T080000Z,20260722T080000Z",
+                beginMillis = instantAt("2026-07-15T08:00", "UTC"),
+                isAllDay = false,
+            ),
+        ).isEqualTo("20260722T080000Z")
+    }
+
+    @Test
+    fun `a split carries nothing when every exclusion is behind it`() {
+        assertThat(
+            exdateAfter("20260708T080000Z", instantAt("2026-07-15T08:00", "UTC"), isAllDay = false),
+        ).isNull()
+        assertThat(exdateAfter(null, 0L, isAllDay = false)).isNull()
+    }
+
+    @Test
+    fun `all-day exclusions split on their UTC date`() {
+        assertThat(
+            exdateAfter("20260708,20260722", instantAt("2026-07-15T00:00", "UTC"), isAllDay = true),
+        ).isEqualTo("20260722")
+    }
+
+    @Test
+    fun `an unreadable exclusion carries nothing across a split`() {
+        assertThat(
+            exdateAfter(
+                "20260722T080000Z,TZID=Europe/Berlin;20260729T100000",
+                instantAt("2026-07-15T08:00", "UTC"),
+                isAllDay = false,
+            ),
+        ).isNull()
+    }
+
+    @Test
+    fun `split exclusions move by the same shift as the new series start`() {
+        // What the split path composes: filter to the tail, then re-time it by the
+        // shift the user applied to the occurrence they split at.
+        val original = julySeries()
+        val carried = shiftedExdate(
+            existingExdate = exdateAfter(
+                "20260716T070000Z",
+                instantAt("2026-07-15T07:00", "UTC"),
+                isAllDay = false,
+            ),
+            original = original,
+            updated = original.atHour(11),
+            zone = berlin,
+        )
+        // 16 July 09:00 Berlin, pushed two hours, is 11:00 Berlin == 09:00Z.
+        assertThat(carried).isEqualTo("20260716T090000Z")
+    }
+
+    @Test
+    fun `nothing to shift yields no exdate`() {
+        assertThat(shiftedExdate(null, julySeries(), julySeries().atHour(10), berlin)).isNull()
+        assertThat(shiftedExdate("  ", julySeries(), julySeries().atHour(10), berlin)).isNull()
+    }
+
     // --- per-event colour ---
 
     @Test