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.

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

@@ -1200,12 +1200,9 @@ class AndroidCalendarDataSource @Inject constructor(
         allDayReminderTimeMinutes: Int,
     ): Long {
         val row = querySeriesRow(eventId)
-        // Deliberately stricter than deleteOccurrence's bare _sync_id check: the
-        // detach path drops the occurrence with EXDATE, which only means anything
-        // on a row that actually recurs. Without an RRULE there is nothing to
-        // exclude from, so such a row keeps the existing path rather than getting
-        // a recurrence set written onto a one-off event. The UI only offers the
-        // scope choice for a recurring event, so neither case is reachable today.
+        // 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)
         }
@@ -1233,46 +1230,24 @@ class AndroidCalendarDataSource @Inject constructor(
      * 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: the insert either fails outright or lands
-     * an orphan row, and the parent's expansion collapses — which is why editing
-     * one occurrence of such a series did nothing at all, and occasionally left a
-     * stray copy behind (Codeberg #234). The reporter's calendar was a Google one
-     * that "shows as on-device", i.e. rows the sync adapter had not stamped yet;
-     * Calendula's own local and contact special-date calendars are permanently in
-     * this shape.
+     * 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.
      *
-     * EXDATE + a standalone row needs no parent link, and is what a detached
-     * instance degrades to when there is no `RECURRENCE-ID` to carry it: the user
-     * sees one edited event where the occurrence was, and the rest of the series
-     * untouched.
+     * 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].
      *
-     * What that costs, plainly, because none of it is recoverable later — the
-     * detached row has *no* stored link back to its series, which is the whole
-     * reason this path exists:
-     * - It stops travelling with the series. Moving the series to another
-     *   calendar leaves it behind ([moveEvent] copies the master and its
-     *   `ORIGINAL_ID` children; this is neither), and deleting the whole series
-     *   leaves it standing where an exception row would have gone with the parent.
-     * - Its EXDATE hole is an absolute instant. Editing the series' *time* for all
-     *   events moves the generated instances but not the hole, so the occurrence
-     *   comes back alongside the detached copy. That staleness predates this path
-     *   — a #47 delete resurrects the same way — but a duplicate is a louder
-     *   symptom than a resurrection, and it wants fixing at the series-update end.
-     * - It is built from the form, not cloned from the parent, so columns the form
-     *   doesn't model are dropped rather than inherited: `ORGANIZER`, `STATUS`,
-     *   and the organizer/resource attendee rows [reconcileAttendees] otherwise
-     *   preserves. Same limitation as [moveEvent]. Rare on the calendars that
-     *   reach this path, which are locally authored, but not impossible.
-     *
-     * Order is deliberate. The insert goes first, so a failure there leaves the
-     * series completely untouched (the same discipline as
-     * [updateEventFromOccurrence]). If the EXDATE update then fails, the new row
-     * is a visible duplicate of an occurrence that is still in the series, so it
-     * is rolled back before the failure surfaces — better a save the user can
-     * retry than a silent duplicate. The reverse order would risk the opposite:
-     * an occurrence excluded from the series with no replacement, i.e. an edit
-     * that quietly deletes.
+     * 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,
@@ -1281,17 +1256,15 @@ class AndroidCalendarDataSource @Inject constructor(
         form: EventForm,
         allDayReminderTimeMinutes: Int,
     ): Long {
-        // Already detached (or deleted): the series no longer contains this
-        // occurrence, so there is nothing here to edit. Reached from a stale
-        // screen still pointing at the parent — without this the EXDATE merge
-        // would fold the repeat away, the update would still report a changed
-        // row, and the save would quietly leave a *second* standalone copy.
+        // 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)
         }
-        // Carries the form's reminders, guests and colour like any new event —
-        // and a fresh UID, because the detached row really is a separate event
-        // now: sharing the parent's would collide with it in .ics restore dedup.
+        // 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,
@@ -1302,10 +1275,9 @@ class AndroidCalendarDataSource @Inject constructor(
             timezone = row.timezone,
             allDay = row.allDay,
         )
-        // Rows touched, not occurrences excluded: this is 1 whenever the series
-        // row still exists. It catches the row disappearing under us, not an
-        // EXDATE the provider's expansion fails to match — that would report
-        // success and leave the duplicate. Same rollback idiom as moveEvent.
+        // 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),
@@ -1326,10 +1298,8 @@ class AndroidCalendarDataSource @Inject constructor(
 
     /**
      * Undo the standalone row [detachOccurrence] inserted before its EXDATE
-     * update failed. Best effort: the caller is already throwing, and a rollback
-     * that itself fails must not replace the real failure with a confusing one.
-     * The worst case is the duplicate we were trying to avoid, which the user can
-     * see and delete — never a lost occurrence.
+     * 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 {

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

@@ -248,18 +248,13 @@ internal fun buildOccurrenceExceptionValues(
  * series rule dropped so [buildEventInsertValues] writes a standalone one-off
  * row (DTSTART + DTEND, no RRULE/DURATION) at the occurrence's own times.
  *
- * This is the "edit only this event" shape for a series with **no `_sync_id`**,
- * where an exception row can't be used at all — see [buildOccurrenceExdateValues]
- * for why the parent link never forms. The occurrence is dropped from the parent
- * with EXDATE and re-created as its own event, which is what a detached instance
- * degrades to without a `RECURRENCE-ID` to carry it.
+ * 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).
  *
- * Dropping the rule mirrors what the exception path gets for free: the provider
- * clears the RRULE it cloned from the parent when an exception carries
- * DTSTART + DURATION ([buildOccurrenceExceptionValues]). Here nothing is cloned,
- * so the rule has to be stripped by hand — leaving it on would insert a second
- * *series* overlapping the first, which is the duplication this path exists to
- * avoid.
+ * 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)
 
@@ -457,14 +452,11 @@ internal fun buildOccurrenceExdateValues(
 
 /**
  * Whether [existingExdate] already excludes the occurrence at [occurrenceMillis]
- * — i.e. this occurrence has already been dropped from the series (deleted, or
- * detached into its own event).
+ * — i.e. it has already been dropped from the series, deleted or detached.
  *
- * Guards the detach path against running twice for the same occurrence, which a
- * stale detail screen still pointing at the parent can otherwise reach. The
- * EXDATE merge folds the repeat away silently and the parent update still
- * reports one row changed, so without this check the second save would leave a
- * *second* standalone copy and call it a success.
+ * 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 exdateContains(
     existingExdate: String?,

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

@@ -265,10 +265,9 @@ fun EventEditScreen(
                 viewModel.reset()
                 onSaved()
             }
-            // A failed save leaves the user on a form that looks exactly as it
-            // did, so the snackbar is the only sign anything happened — it gets
-            // the long duration rather than the default flash (Codeberg #234:
-            // the failure read as "nothing happens at all").
+            // 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, duration = SnackbarDuration.Long)

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

@@ -755,14 +755,13 @@ class EventEditViewModel @Inject constructor(
             } catch (e: SecurityException) {
                 SaveUiState.NeedsPermission
             } catch (e: NoSuchEventException) {
-                // The write found the event (or the occurrence) already gone —
-                // the same answer the pre-check gives, and a far better one than
-                // a bare "couldn't save" for something that no longer exists.
+                // 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 no trace at all to report (Codeberg #234).
-                // Scope and event id only — never the form's content.
+                // 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

@@ -571,14 +571,11 @@ class EventWriteMapperTest {
             times = detached.toWriteTimes(berlin),
         )
         assertThat(values[CalendarContract.Events.TITLE]).isEqualTo("Moved")
-        // The rule must not survive: without a _sync_id nothing clears an
-        // inherited RRULE the way the exception path's DTSTART + DURATION does,
-        // so keeping it would insert a second *series* overlapping the first
+        // 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 — the invariant buildEventInsertValues
-        // holds for every non-recurring event.
+        // 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")
@@ -586,9 +583,8 @@ class EventWriteMapperTest {
 
     @Test
     fun `a detached occurrence carries every edited field onto the new row`() {
-        // The detached row is built from the form rather than cloned from the
-        // parent, so anything the user edited has to survive the trip — a field
-        // dropped here is an edit silently lost.
+        // 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",
@@ -612,12 +608,10 @@ class EventWriteMapperTest {
             .isEqualTo(CalendarContract.Events.AVAILABILITY_FREE)
         assertThat(values[CalendarContract.Events.ACCESS_LEVEL])
             .isEqualTo(CalendarContract.Events.ACCESS_PRIVATE)
-        // The pinned zone survives too — a detached occurrence must not be
-        // silently re-anchored to the device.
+        // 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 and guests aren't columns — the insert path seeds them from
-        // the form, so they only have to survive on the form itself.
+        // Reminders aren't columns; the insert path seeds them from the form.
         assertThat(detached.reminders).containsExactly(10)
     }
 
@@ -645,9 +639,8 @@ class EventWriteMapperTest {
 
     @Test
     fun `the detached row lands exactly where the parent's exdate removes it`() {
-        // The two halves of the no-_sync_id edit have to agree, or the user sees
-        // the occurrence twice or not at all. With the time left untouched, the
-        // EXDATE stamp and the detached row's DTSTART describe the same instant.
+        // 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
 
@@ -702,8 +695,7 @@ class EventWriteMapperTest {
 
     @Test
     fun `an occurrence already excluded is recognised, timed and all-day`() {
-        // Detaching twice would fold the repeated EXDATE away and still report a
-        // changed row, leaving a second standalone copy of one occurrence.
+        // Detaching twice would leave a second standalone copy.
         assertThat(
             exdateContains("20260611T080000Z", 1_781_164_800_000L, isAllDay = false),
         ).isTrue()
@@ -724,8 +716,7 @@ class EventWriteMapperTest {
 
     @Test
     fun `an exclusion is found anywhere in a multi-entry exdate list`() {
-        // Whitespace after a comma is legal in the stored column and must not
-        // hide an exclusion — that would let a duplicate through.
+        // Whitespace after a comma is legal in the stored column.
         assertThat(
             exdateContains(
                 "20260604T080000Z, 20260611T080000Z,20260618T080000Z",