docs: trim the #234 comments to the load-bearing facts

The detach path's KDoc and inline comments restated the bug narrative that
already lives in the commit message and the issue. Keep what a reader of
the code needs — why the branch exists, what the detached row loses, and
why the insert precedes the EXDATE update — and drop the rest.

CHANGELOG.md

@@ -8,16 +8,16 @@ 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]).
+- **"Only this event" now actually saves your edit.** On some calendars —
+  including Google ones that still show as on-device, and any local calendar —
+  editing a single occurrence of a repeating event did nothing at all: the scope
+  dialog closed, the edit screen stayed put, and saving again just repeated it.
+  Android can only attach a single-occurrence change to its series once the
+  calendar has been synced at least once, so on those calendars the change had
+  nowhere to go. Calendula now removes that one occurrence from the series and
+  saves the edit as its own event instead, which is what you see either way. A
+  save that does fail also says so for longer, rather than flashing past
+  ([#234]).
 
 ## [2.19.3] — 2026-08-22
 
@@ -1483,4 +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
+[#234]: https://codeberg.org/jlmakiola/calendula/issues/234

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

@@ -232,10 +232,15 @@ interface CalendarDataSource {
     ): Long
 
     /**
-     * Change a single occurrence of a recurring event by inserting a
-     * modified-occurrence exception at [beginMillis] (the occurrence's
-     * `Instances.BEGIN`) carrying [form]'s values; returns the exception
-     * row's `Events._ID`. [allDayReminderTimeMinutes]: see [insertEvent].
+     * Change a single occurrence of a recurring event at [beginMillis] (the
+     * occurrence's `Instances.BEGIN`) to [form]'s values; returns the
+     * `Events._ID` of the row now holding them.
+     *
+     * A series with a `_sync_id` gets a modified-occurrence exception. One
+     * without gets the occurrence excluded from the parent via EXDATE plus a
+     * standalone event carrying the edits — an exception cannot link to its
+     * parent there (Codeberg #234, the same constraint as [deleteOccurrence]).
+     * [allDayReminderTimeMinutes]: see [insertEvent].
      */
     fun updateOccurrence(
         eventId: Long,
@@ -976,12 +981,10 @@ class AndroidCalendarDataSource @Inject constructor(
         updated: EventForm,
         allDayReminderTimeMinutes: Int,
     ) {
-        val row = querySeriesRow(eventId)
         val values = buildEventUpdateValues(
             original = original,
             updated = updated,
-            seriesDtStartMillis = row.dtStartMillis,
-            seriesExdate = row.exdate,
+            seriesDtStartMillis = querySeriesRow(eventId).dtStartMillis,
             zone = ZoneId.systemDefault(),
         )
         if (values.isNotEmpty()) {
@@ -1196,6 +1199,13 @@ class AndroidCalendarDataSource @Inject constructor(
         form: EventForm,
         allDayReminderTimeMinutes: Int,
     ): Long {
+        val row = querySeriesRow(eventId)
+        // Stricter than deleteOccurrence's bare _sync_id check: EXDATE only means
+        // something on a row that recurs, so a non-recurring one keeps the
+        // exception path rather than getting a recurrence set written onto it.
+        if (row.syncId == null && !row.rrule.isNullOrBlank()) {
+            return detachOccurrence(eventId, beginMillis, row, form, allDayReminderTimeMinutes)
+        }
         // The provider clones the series row and applies these values on top.
         val values = buildOccurrenceExceptionValues(
             form = form,
@@ -1214,6 +1224,89 @@ class AndroidCalendarDataSource @Inject constructor(
         return exceptionId
     }
 
+    /**
+     * "Edit only this event" on a series with **no `_sync_id`**: drop the
+     * occurrence from the parent with EXDATE and insert the edited values as a
+     * standalone event on the same calendar.
+     *
+     * A modified exception attaches to its parent only through `ORIGINAL_SYNC_ID`,
+     * exactly like the cancelled one [deleteOccurrence] documents; with no
+     * `_sync_id` the link never forms and the edit is lost (Codeberg #234).
+     * EXDATE plus a standalone row needs no link — what a detached instance
+     * degrades to without a `RECURRENCE-ID` to carry it.
+     *
+     * The detached row keeps no stored link back to its series, so: it no longer
+     * travels with it ([moveEvent] copies the master and its `ORIGINAL_ID`
+     * children, and this is neither); its EXDATE hole is an absolute instant, so
+     * re-timing the whole series brings the occurrence back beside the copy (a
+     * #47 delete resurrects the same way); and it is built from the form, not
+     * cloned, so `ORGANIZER`, `STATUS` and the attendee rows [reconcileAttendees]
+     * preserves are dropped — the same limitation as [moveEvent].
+     *
+     * Insert first, so a failure leaves the series untouched
+     * ([updateEventFromOccurrence]'s discipline); roll the new row back if the
+     * EXDATE update then fails, since it would be a visible duplicate. The
+     * reverse order risks the worse outcome — an excluded occurrence with no
+     * replacement, i.e. an edit that quietly deletes.
+     */
+    private fun detachOccurrence(
+        eventId: Long,
+        beginMillis: Long,
+        row: SeriesRow,
+        form: EventForm,
+        allDayReminderTimeMinutes: Int,
+    ): Long {
+        // Already detached (or deleted) from a stale screen still pointing at the
+        // parent: the EXDATE merge would fold the repeat away and still report a
+        // changed row, quietly leaving a *second* standalone copy.
+        if (exdateContains(row.exdate, beginMillis, isAllDay = row.allDay != 0)) {
+            throw NoSuchEventException(eventId)
+        }
+        // Reminders, guests and colour come along like any new event, and so does
+        // a fresh UID — the detached row is a separate event now, and sharing the
+        // parent's would collide with it in .ics restore dedup.
+        val detachedId = insertEvent(form.toDetachedOccurrence(), allDayReminderTimeMinutes)
+        val values = buildOccurrenceExdateValues(
+            existingExdate = row.exdate,
+            occurrenceMillis = beginMillis,
+            dtStartMillis = row.dtStartMillis,
+            rrule = row.rrule,
+            duration = row.duration,
+            timezone = row.timezone,
+            allDay = row.allDay,
+        )
+        // Rows touched, not occurrences excluded — 1 whenever the series row still
+        // exists. It catches the row disappearing under us, not an EXDATE the
+        // provider's expansion fails to match.
+        val updatedRows = try {
+            resolver.update(
+                ContentUris.withAppendedId(CalendarContract.Events.CONTENT_URI, eventId),
+                values.toContentValues(), null, null,
+            )
+        } catch (t: Throwable) {
+            rollBackDetached(detachedId)
+            throw t
+        }
+        if (updatedRows == 0) {
+            rollBackDetached(detachedId)
+            throw WriteFailedException(
+                "exdate occurrence for edit, event id=$eventId begin=$beginMillis",
+            )
+        }
+        return detachedId
+    }
+
+    /**
+     * Undo the standalone row [detachOccurrence] inserted before its EXDATE
+     * update failed. Best effort: the caller is already throwing, and the worst
+     * case is the duplicate we were avoiding — never a lost occurrence.
+     */
+    private fun rollBackDetached(detachedId: Long) {
+        runCatching { deleteEvent(detachedId) }.onFailure {
+            Log.w(TAG, "Failed to roll back detached occurrence $detachedId", it)
+        }
+    }
+
     override fun updateEventFromOccurrence(
         eventId: Long,
         beginMillis: Long,
@@ -1230,66 +1323,10 @@ 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

@@ -10,9 +10,6 @@ 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. */
@@ -137,21 +134,18 @@ 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, RRULE and EXDATE cleared;
+ * - non-recurring result → DTSTART/DTEND, DURATION and RRULE 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, and the row's exclusions
- *   ([seriesExdate], the current EXDATE) travel with the anchor. This keeps past
- *   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.
+ *   replaces DTEND, RRULE is written. This keeps past 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()) {
@@ -191,10 +185,6 @@ 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)
@@ -216,14 +206,6 @@ 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) }
     }
 }
 
@@ -261,6 +243,21 @@ internal fun buildOccurrenceExceptionValues(
     putAll(eventColorColumns(form.colorKey, form.color))
 }
 
+/**
+ * The form as a **detached occurrence**: the same edited values, with the
+ * series rule dropped so [buildEventInsertValues] writes a standalone one-off
+ * row (DTSTART + DTEND, no RRULE/DURATION) at the occurrence's own times.
+ *
+ * The "edit only this event" shape for a series with **no `_sync_id`**, where an
+ * exception row can't attach to its parent at all (Codeberg #234).
+ *
+ * The exception path gets the rule dropped for free — the provider clears the
+ * RRULE it cloned when an exception carries DTSTART + DURATION
+ * ([buildOccurrenceExceptionValues]). Here nothing is cloned, so it is stripped
+ * by hand; leaving it on would insert a second *series* overlapping the first.
+ */
+internal fun EventForm.toDetachedOccurrence(): EventForm = copy(rrule = null)
+
 /**
  * Raw provider snapshot of a master/one-off Events row, enough to re-insert it
  * verbatim on another calendar (a calendar move is copy+delete — `CALENDAR_ID`
@@ -438,7 +435,11 @@ internal fun buildOccurrenceExdateValues(
     allDay: Int,
 ): Map<String, Any?> {
     val stamp = formatExdateStamp(occurrenceMillis, isAllDay = allDay != 0)
-    val merged = (exdateStamps(existingExdate) + stamp).distinct().joinToString(",")
+    val existing = existingExdate?.split(',')
+        ?.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,
@@ -450,121 +451,38 @@ 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.
+ * Whether [existingExdate] already excludes the occurrence at [occurrenceMillis]
+ * — i.e. it has already been dropped from the series, deleted or detached.
  *
- * 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.
+ * Guards the detach path against running twice from a stale screen: the EXDATE
+ * merge folds the repeat away silently and the update still reports one row
+ * changed, so a second save would leave a second standalone copy.
  */
-internal fun shiftedExdate(
+internal fun exdateContains(
     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(",")
+    occurrenceMillis: Long,
+    isAllDay: Boolean,
+): Boolean {
+    val stamp = formatExdateStamp(occurrenceMillis, isAllDay)
+    return existingExdate?.split(',')?.any { it.trim() == stamp } == true
 }
 
-/**
- * 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 =
-    formatExdateStamp(
-        local = Instant.ofEpochMilli(occurrenceMillis).atZone(ZoneOffset.UTC).toLocalDateTime(),
-        isAllDay = isAllDay,
-        zone = ZoneOffset.UTC,
-    )
-
-/**
- * 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)
+private fun formatExdateStamp(occurrenceMillis: Long, isAllDay: Boolean): String {
+    val utc = Instant.ofEpochMilli(occurrenceMillis).atZone(ZoneOffset.UTC)
+    return if (isAllDay) {
+        "%04d%02d%02d".format(utc.year, utc.monthValue, utc.dayOfMonth)
     } else {
-        local.atZone(zone).withZoneSameInstant(ZoneOffset.UTC).format(TIMED_EXDATE)
+        "%04d%02d%02dT%02d%02d%02dZ".format(
+            utc.year, utc.monthValue, utc.dayOfMonth,
+            utc.hour, utc.minute, utc.second,
+        )
     }
-
-/**
- * [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/main/java/de/jeanlucmakiola/calendula/ui/edit/EventEditScreen.kt

@@ -64,6 +64,7 @@ import androidx.compose.material3.Scaffold
 import androidx.compose.material3.SegmentedButton
 import androidx.compose.material3.SegmentedButtonDefaults
 import androidx.compose.material3.SingleChoiceSegmentedButtonRow
+import androidx.compose.material3.SnackbarDuration
 import androidx.compose.material3.SnackbarHost
 import androidx.compose.material3.SnackbarHostState
 import androidx.compose.material3.Surface
@@ -264,13 +265,16 @@ fun EventEditScreen(
                 viewModel.reset()
                 onSaved()
             }
+            // A failed save leaves the form looking unchanged, so the snackbar is
+            // the only sign anything happened — long rather than the default
+            // flash (Codeberg #234: it read as "nothing happens at all").
             SaveUiState.Failed -> {
                 viewModel.consumeSaveResult()
-                snackbarHostState.showSnackbar(saveFailedMessage)
+                snackbarHostState.showSnackbar(saveFailedMessage, duration = SnackbarDuration.Long)
             }
             SaveUiState.NeedsPermission -> {
                 viewModel.consumeSaveResult()
-                snackbarHostState.showSnackbar(writeDeniedMessage)
+                snackbarHostState.showSnackbar(writeDeniedMessage, duration = SnackbarDuration.Long)
             }
             // AwaitingScope/AwaitingConflict/Gone render as dialogs below.
             else -> Unit

app/src/main/java/de/jeanlucmakiola/calendula/ui/edit/EventEditViewModel.kt

@@ -1,5 +1,6 @@
 package de.jeanlucmakiola.calendula.ui.edit
 
+import android.util.Log
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
@@ -56,6 +57,8 @@ import kotlin.time.Duration.Companion.minutes
 import kotlin.time.Instant
 import javax.inject.Inject
 
+private const val TAG = "EventEdit"
+
 /**
  * Where a prefilled [EventEditViewModel.openImported] form came from. The sources
  * want different reminder handling (#49), and differ in whether they own the
@@ -751,7 +754,15 @@ class EventEditViewModel @Inject constructor(
                 throw e
             } catch (e: SecurityException) {
                 SaveUiState.NeedsPermission
+            } catch (e: NoSuchEventException) {
+                // The event or occurrence is already gone: the same answer the
+                // pre-check gives, and better than a bare "couldn't save".
+                SaveUiState.Gone
             } catch (e: Exception) {
+                // The user only gets a generic snackbar, so without this a failed
+                // write leaves nothing to report (Codeberg #234). Scope and event
+                // id only — never the form's content.
+                Log.w(TAG, "Save failed (scope=$scope, eventId=${target?.eventId})", e)
                 SaveUiState.Failed
             }
         }

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

@@ -128,8 +128,7 @@ class EventWriteMapperTest {
         original: EventForm,
         updated: EventForm,
         series: Long = seriesStart,
-        exdate: String? = null,
-    ): Map<String, Any?> = buildEventUpdateValues(original, updated, series, exdate, berlin)
+    ): Map<String, Any?> = buildEventUpdateValues(original, updated, series, berlin)
 
     /** The instant [local] names in [zoneId], as the provider would store it. */
     private fun instantAt(local: String, zoneId: String): Long =
@@ -559,237 +558,172 @@ 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)),
-    )
+    // --- toDetachedOccurrence ("edit only this event", no _sync_id) ---
 
     @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")
-    }
+    fun `a detached occurrence drops the series rule and becomes a one-off row`() {
+        val edited = form().copy(title = "Moved", rrule = "FREQ=WEEKLY;BYDAY=TH")
+        val detached = edited.toDetachedOccurrence()
 
-    @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",
+        val values = buildEventInsertValues(
+            form = detached,
+            uid = "uid@calendula",
+            times = detached.toWriteTimes(berlin),
         )
-        // The exclusion still reads 09:00 — now 09:00 in Tokyo (+9) == 00:00Z.
-        assertThat(values[CalendarContract.Events.EXDATE]).isEqualTo("20260716T000000Z")
+        assertThat(values[CalendarContract.Events.TITLE]).isEqualTo("Moved")
+        // A surviving rule would insert a second *series* overlapping the first
+        // (Codeberg #234's stray duplicate).
+        assertThat(values).doesNotContainKey(CalendarContract.Events.RRULE)
+        assertThat(values).doesNotContainKey(CalendarContract.Events.DURATION)
+        // A one-off row carries DTEND rather than a duration.
+        assertThat(values[CalendarContract.Events.DTSTART]).isEqualTo(1_781_164_800_000L)
+        assertThat(values[CalendarContract.Events.DTEND]).isEqualTo(1_781_170_200_000L)
+        assertThat(values[CalendarContract.Events.EVENT_TIMEZONE]).isEqualTo("Europe/Berlin")
     }
 
     @Test
-    fun `an all-day series move shifts its exclusions by whole days`() {
-        val series = instantAt("2026-07-01T00:00", "UTC")
-        val original = form(
+    fun `a detached occurrence carries every edited field onto the new row`() {
+        // Built from the form, not cloned from the parent: a field dropped here
+        // is an edit silently lost.
+        val edited = form(timezone = "America/New_York").copy(
+            title = "  Standup  ",
+            location = "Room 2",
+            description = "notes",
+            reminders = listOf(10),
+            availability = Availability.Free,
+            accessLevel = AccessLevel.Private,
+            rrule = "FREQ=DAILY",
+        )
+        val detached = edited.toDetachedOccurrence()
+
+        val values = buildEventInsertValues(
+            form = detached,
+            uid = "uid@calendula",
+            times = detached.toWriteTimes(berlin),
+        )
+        assertThat(values[CalendarContract.Events.TITLE]).isEqualTo("Standup")
+        assertThat(values[CalendarContract.Events.EVENT_LOCATION]).isEqualTo("Room 2")
+        assertThat(values[CalendarContract.Events.DESCRIPTION]).isEqualTo("notes")
+        assertThat(values[CalendarContract.Events.AVAILABILITY])
+            .isEqualTo(CalendarContract.Events.AVAILABILITY_FREE)
+        assertThat(values[CalendarContract.Events.ACCESS_LEVEL])
+            .isEqualTo(CalendarContract.Events.ACCESS_PRIVATE)
+        // The pinned zone survives — never re-anchored to the device.
+        assertThat(values[CalendarContract.Events.EVENT_TIMEZONE]).isEqualTo("America/New_York")
+        assertThat(values[CalendarContract.Events.UID_2445]).isEqualTo("uid@calendula")
+        // Reminders aren't columns; the insert path seeds them from the form.
+        assertThat(detached.reminders).containsExactly(10)
+    }
+
+    @Test
+    fun `a detached all-day occurrence stays on UTC midnights`() {
+        val edited = 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)),
+            start = LocalDateTime(LocalDate(2026, 6, 11), LocalTime(0, 0)),
+            end = LocalDateTime(LocalDate(2026, 6, 11), LocalTime(0, 0)),
+        ).copy(title = "Birthday", rrule = "FREQ=YEARLY")
+        val detached = edited.toDetachedOccurrence()
+
+        val values = buildEventInsertValues(
+            form = detached,
+            uid = "uid@calendula",
+            times = detached.toWriteTimes(berlin),
         )
-
-        assertThat(update(original, moved, series, "20260722")[CalendarContract.Events.EXDATE])
-            .isEqualTo("20260724")
+        assertThat(values[CalendarContract.Events.ALL_DAY]).isEqualTo(1)
+        assertThat(values[CalendarContract.Events.EVENT_TIMEZONE]).isEqualTo("UTC")
+        assertThat(values[CalendarContract.Events.DTSTART]).isEqualTo(1_781_136_000_000L)
+        // Exclusive DTEND — the next UTC midnight.
+        assertThat(values[CalendarContract.Events.DTEND]).isEqualTo(1_781_222_400_000L)
+        assertThat(values).doesNotContainKey(CalendarContract.Events.RRULE)
     }
 
     @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")
+    fun `the detached row lands exactly where the parent's exdate removes it`() {
+        // The two halves must agree on the instant, or the user sees the
+        // occurrence twice or not at all.
+        val edited = form().copy(title = "Renamed", rrule = "FREQ=WEEKLY")
+        val occurrenceMillis = 1_781_164_800_000L
+
+        val parent = buildOccurrenceExdateValues(
+            existingExdate = null,
+            occurrenceMillis = occurrenceMillis,
+            dtStartMillis = 1_780_560_000_000L,
+            rrule = "FREQ=WEEKLY",
+            duration = "P5400S",
+            timezone = "Europe/Berlin",
+            allDay = 0,
+        )
+        val detached = edited.toDetachedOccurrence()
+        val inserted = buildEventInsertValues(
+            form = detached,
+            uid = "uid@calendula",
+            times = detached.toWriteTimes(berlin),
+        )
+        assertThat(parent[CalendarContract.Events.EXDATE]).isEqualTo("20260611T080000Z")
+        assertThat(inserted[CalendarContract.Events.DTSTART]).isEqualTo(occurrenceMillis)
+        // The parent keeps its own anchor and rule — only this occurrence leaves.
+        assertThat(parent[CalendarContract.Events.DTSTART]).isEqualTo(1_780_560_000_000L)
+        assertThat(parent[CalendarContract.Events.RRULE]).isEqualTo("FREQ=WEEKLY")
     }
 
     @Test
-    fun `switching a series back to timed rewrites its exclusions as instants`() {
-        val series = instantAt("2026-07-01T00:00", "UTC")
-        val original = form(
+    fun `a detached all-day occurrence matches its date-only exdate stamp`() {
+        val parent = buildOccurrenceExdateValues(
+            existingExdate = null,
+            occurrenceMillis = 1_781_136_000_000L, // 2026-06-11T00:00:00Z
+            dtStartMillis = 1_749_600_000_000L,
+            rrule = "FREQ=YEARLY",
+            duration = "P1D",
+            timezone = "UTC",
+            allDay = 1,
+        )
+        val detached = 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)),
+            start = LocalDateTime(LocalDate(2026, 6, 11), LocalTime(0, 0)),
+            end = LocalDateTime(LocalDate(2026, 6, 11), LocalTime(0, 0)),
+        ).copy(rrule = "FREQ=YEARLY").toDetachedOccurrence()
+        val inserted = buildEventInsertValues(
+            form = detached,
+            uid = "uid@calendula",
+            times = detached.toWriteTimes(berlin),
         )
-        // 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")
+        assertThat(parent[CalendarContract.Events.EXDATE]).isEqualTo("20260611")
+        assertThat(inserted[CalendarContract.Events.DTSTART]).isEqualTo(1_781_136_000_000L)
     }
 
-    @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)
-    }
+    // --- exdateContains (guards a second detach of the same occurrence) ---
 
     @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.
+    fun `an occurrence already excluded is recognised, timed and all-day`() {
+        // Detaching twice would leave a second standalone copy.
         assertThat(
-            exdateAfter(
-                existingExdate = "20260708T080000Z,20260715T080000Z,20260722T080000Z",
-                beginMillis = instantAt("2026-07-15T08:00", "UTC"),
+            exdateContains("20260611T080000Z", 1_781_164_800_000L, isAllDay = false),
+        ).isTrue()
+        assertThat(
+            exdateContains("20260611", 1_781_136_000_000L, isAllDay = true),
+        ).isTrue()
+    }
+
+    @Test
+    fun `an occurrence not in the exdate list is not mistaken for an excluded one`() {
+        assertThat(exdateContains(null, 1_781_164_800_000L, isAllDay = false)).isFalse()
+        assertThat(exdateContains("", 1_781_164_800_000L, isAllDay = false)).isFalse()
+        // A neighbouring occurrence must not match — the guard is per-instant.
+        assertThat(
+            exdateContains("20260610T080000Z", 1_781_164_800_000L, isAllDay = false),
+        ).isFalse()
+    }
+
+    @Test
+    fun `an exclusion is found anywhere in a multi-entry exdate list`() {
+        // Whitespace after a comma is legal in the stored column.
+        assertThat(
+            exdateContains(
+                "20260604T080000Z, 20260611T080000Z,20260618T080000Z",
+                1_781_164_800_000L,
                 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()
+        ).isTrue()
     }
 
     // --- per-event colour ---