feat: support safe recurrence additions

Parse, persist, expand, and round-trip compatible RDATE values while preserving whole-series TUI behavior and conservative rewrite guards.

Verified: normal, warning-as-error, and ASan/UBSan builds pass all 9 suites; storage failure paths preserve calendar and backup bytes; live PTY restores terminal state.

README.md

@@ -75,8 +75,10 @@ source that fails event validation or that Nocal cannot safely round-trip.
 
 Nocal expands and safely round-trips a focused iCalendar recurrence subset:
 daily, weekly, monthly, and yearly rules with interval, count or until, common
-weekly/monthly/yearly selectors, `EXDATE`, floating times, UTC, and system IANA
-`TZID` names. Recurring instances are individually navigable; edit and delete
+weekly/monthly/yearly selectors, compatible DATE or DATE-TIME `RDATE` additions,
+`EXDATE`, floating times, UTC, and system IANA `TZID` names. Occurrences merge
+`DTSTART`, rule expansion, and `RDATE`, remove duplicate starts, and then apply
+`EXDATE`. Recurring instances are individually navigable; edit and delete
 clearly operate on the entire series.
 
 Search expands recurring matches within five years on either side of the
@@ -88,8 +90,9 @@ agenda, appointment focus, and search. Visibility and agenda position are
 session-only presentation state; saves always retain events from hidden
 calendars.
 
-Calendars containing features this version cannot preserve—such as `RDATE`,
-detached recurrence overrides, ordinal `BYDAY`, embedded `VTIMEZONE`
+Calendars containing features this version cannot preserve—such as `RDATE`
+periods or values incompatible with the event's `DTSTART` time basis or `TZID`,
+detached `RECURRENCE-ID` overrides, ordinal `BYDAY`, embedded `VTIMEZONE`
 definitions, alarms, or attendees—remain browsable but read-only. This guard
 prevents a local edit from silently discarding unknown data.
 

docs/ARCHITECTURE.md

@@ -36,8 +36,11 @@ requested time window and return values that point back to their source series,
 preserving series-level storage and mutation semantics. The supported rule
 surface is deliberately bounded to daily/weekly/monthly/yearly frequency,
 interval, count or until, weekly `BYDAY`, monthly `BYMONTHDAY`, yearly
-`BYMONTH`, and `EXDATE`. Invalid metadata retains at most the base event rather
-than crashing a render.
+`BYMONTH`, compatible DATE or DATE-TIME `RDATE`, and `EXDATE`. An occurrence set
+merges `DTSTART`, rule expansion, and additional `RDATE` starts, deduplicates by
+start, and then subtracts exclusions. Mutations continue to address the source
+series as a whole. Invalid metadata retains at most the base event rather than
+crashing a render.
 
 Search matching is a pure domain predicate over normalized event text; the TUI
 owns result presentation and occurrence identity. Recurring searches expand a
@@ -107,12 +110,13 @@ combined with any of the other modes.
 
 The current writer deliberately refuses to mutate an existing file when the
 loader encounters information it cannot round-trip, including recurrence
-overrides, `RDATE`, custom `VTIMEZONE` definitions, alarms, attendees, unknown
-properties, or malformed components. Supported recurrence rules, exclusions,
-and system IANA time-zone identifiers round-trip semantically. Browsing remains
-available for unsupported files. This conservative boundary is more important
-than partial editing because a successful-looking edit must not erase unrelated
-calendar data.
+overrides, `RDATE` periods or values incompatible with `DTSTART`'s time basis or
+`TZID`, custom `VTIMEZONE` definitions, alarms, attendees, unknown properties,
+or malformed components. Supported recurrence rules, compatible additional
+starts, exclusions, and system IANA time-zone identifiers round-trip
+semantically. Browsing remains available for unsupported files. This
+conservative boundary is more important than partial editing because a
+successful-looking edit must not erase unrelated calendar data.
 
 Provider synchronization will not write directly into this UI file. It will use
 a transaction-capable local cache and preserve remote ETags/sync tokens in a

docs/PRODUCT.md

@@ -89,22 +89,28 @@ read-only instead of being discarded. Saves reject external changes, retain a
 last-known-good backup, and feed bounded session undo/redo history. Supported
 recurring instances appear throughout the month, preserve civil time across
 daylight-saving changes, and expose their source zone and whole-series mutation
-semantics in the reader. `/` searches occurrence-aware title, description,
-location, and calendar-ID matches in a finite ten-year window centered on the
-selected date. `c` toggles session-only calendar visibility consistently across
-the grid, appointment focus, and search without filtering the model supplied to
-persistence. `g` opens an occurrence-aware agenda at the selected month date;
-navigation is bounded to consecutive 42-day windows and `Enter` returns to the
-exact occurrence in the month grid. `Esc` or `g` closes the agenda without
-changing the month selection unless an occurrence was chosen. Hidden calendars
-remain filtered there, while calendar selection and search can overlay the
-agenda. Agenda navigation never persists state, and add/edit/delete remain in
-the month workflow. Week-start selection rotates only the month grid, header,
-and the visible range used by its month queries; storage, agenda windows, and
+semantics in the reader. A supported recurrence set combines `DTSTART`, rule
+expansion, and compatible DATE or DATE-TIME `RDATE` starts, deduplicates starts,
+and then removes `EXDATE` exclusions. `/` searches occurrence-aware title,
+description, location, and calendar-ID matches in a finite ten-year window
+centered on the selected date. `c` toggles session-only calendar visibility
+consistently across the grid, appointment focus, and search without filtering
+the model supplied to persistence. `g` opens an occurrence-aware agenda at the
+selected month date; navigation is bounded to consecutive 42-day windows and
+`Enter` returns to the exact occurrence in the month grid. `Esc` or `g` closes
+the agenda without changing the month selection unless an occurrence was
+chosen. Hidden calendars remain filtered there, while calendar selection and
+search can overlay the agenda. Agenda navigation never persists state, and
+add/edit/delete remain in the month workflow. Week-start selection rotates only
+the month grid, header, and the visible range used by its month queries;
+storage, agenda windows, and
 recurrence rules are unchanged. The default remains Monday for backward
 compatibility. The CLI accepts the exact lowercase values `monday`, `tuesday`,
-`wednesday`, `thursday`, `friday`, `saturday`, and `sunday`. The next local-data
-work adds advanced recurrence overrides and rule editing.
+`wednesday`, `thursday`, `friday`, `saturday`, and `sunday`. `RDATE` periods,
+values incompatible with the event's `DTSTART` time basis or `TZID`, detached
+`RECURRENCE-ID` overrides, and embedded `VTIMEZONE` definitions remain
+read-only. Remaining local-data work includes detached overrides and rule
+editing.
 
 ## Local file interchange
 

docs/ROADMAP.md

@@ -8,7 +8,8 @@
 - Validated add/edit/delete forms with confirmation and failure rollback
 - Guarded atomic `.ics` persistence, advisory locking, and round-trip tests
 - Bounded session undo/redo, exact external-change detection, and backup recovery
-- Windowed recurrence expansion, EXDATE, IANA TZID, and multi-day segment cues
+- Windowed recurrence expansion, compatible RDATE, EXDATE, IANA TZID, and
+  multi-day segment cues
 - Occurrence-aware appointment search with exact result-to-grid navigation
 - Session calendar toggles shared by month rendering, focus, and search
 - Read-only 42-day agenda with bounded recurrence and exact return navigation
@@ -19,7 +20,8 @@
 
 ## 0.1 — complete local calendar
 
-- Advanced recurrence editing, RDATE/overrides, and embedded VTIMEZONE support
+- Advanced recurrence rule editing and detached RECURRENCE-ID overrides
+- Embedded VTIMEZONE support
 - Screen-reader-friendly linear view and full Unicode display-width handling
 
 ## 0.2 — durable cache and provider boundary

include/nocal/domain/event.hpp

@@ -39,6 +39,7 @@ struct Event {
     TimeBasis time_basis{TimeBasis::utc};
     std::string time_zone;
     std::optional<RecurrenceRule> recurrence;
+    std::vector<TimePoint> recurrence_additions;
     std::vector<TimePoint> recurrence_exceptions;
 };
 
@@ -55,4 +56,9 @@ struct Calendar {
     return event.end >= event.start;
 }
 
+[[nodiscard]] constexpr bool is_recurring(const Event& event) noexcept
+{
+    return event.recurrence.has_value() || !event.recurrence_additions.empty();
+}
+
 } // namespace nocal

src/domain/calendar_transfer.cpp

@@ -20,6 +20,7 @@ namespace {
            left.time_basis == right.time_basis &&
            left.time_zone == right.time_zone &&
            left.recurrence == right.recurrence &&
+           left.recurrence_additions == right.recurrence_additions &&
            left.recurrence_exceptions == right.recurrence_exceptions;
 }
 

src/domain/event_query.cpp

@@ -86,6 +86,24 @@ template <class TimePointType>
            event.recurrence_exceptions.end();
 }
 
+void append_occurrence(EventOccurrences& result, const Event& event,
+                       TimePoint start, TimePoint finish, std::size_t ordinal,
+                       TimePoint begin, TimePoint end,
+                       bool apply_exception = true)
+{
+    if ((apply_exception && is_exception(event, start)) ||
+        !overlaps(start, finish, begin, end)) {
+        return;
+    }
+    const auto duplicate = std::find_if(
+        result.begin(), result.end(), [&event, start](const EventOccurrence& value) {
+            return value.source == &event && value.start == start;
+        });
+    if (duplicate == result.end()) {
+        result.push_back({&event, start, finish, ordinal});
+    }
+}
+
 [[nodiscard]] std::tm process_local_tm(std::time_t time)
 {
     std::tm result{};
@@ -334,10 +352,8 @@ void append_candidate(EventOccurrences& result, const Event& event,
             candidate_end =
                 project_to_system(event, *civil_end, projection.zone);
         }
-        if (!is_exception(event, candidate_start) &&
-            overlaps(candidate_start, candidate_end, begin, end)) {
-            result.push_back({&event, candidate_start, candidate_end, ordinal});
-        }
+        append_occurrence(result, event, candidate_start, candidate_end, ordinal,
+                          begin, end);
     } catch (const std::exception&) {
         // A bad zone, an out-of-range conversion, or a nonexistent civil time
         // invalidates only this generated occurrence. Queries remain noexcept
@@ -345,6 +361,51 @@ void append_candidate(EventOccurrences& result, const Event& event,
     }
 }
 
+void append_recurrence_additions(EventOccurrences& result, const Event& event,
+                                 const Projection& projection, TimePoint begin,
+                                 TimePoint end)
+{
+    const auto duration =
+        event.time_basis == TimeBasis::utc
+            ? checked_difference(event.end.time_since_epoch(),
+                                 event.start.time_since_epoch())
+            : checked_difference(projection.end.time_since_epoch(),
+                                 projection.start.time_since_epoch());
+    if (!duration) {
+        return;
+    }
+
+    for (std::size_t index = 0; index < event.recurrence_additions.size();
+         ++index) {
+        try {
+            const auto candidate_start = event.recurrence_additions[index];
+            TimePoint candidate_end;
+            if (event.time_basis == TimeBasis::utc) {
+                const auto end_value = checked_add(candidate_start, *duration);
+                if (!end_value) {
+                    continue;
+                }
+                candidate_end = *end_value;
+            } else {
+                const auto candidate_civil =
+                    project_to_civil(event, candidate_start, projection.zone);
+                const auto civil_end = checked_add(candidate_civil, *duration);
+                if (!civil_end) {
+                    continue;
+                }
+                candidate_end =
+                    project_to_system(event, *civil_end, projection.zone);
+            }
+            const auto ordinal = index + 1U;
+            append_occurrence(result, event, candidate_start, candidate_end,
+                              ordinal, begin, end);
+        } catch (const std::exception&) {
+            // An invalid zone, nonexistent civil end, or out-of-range value
+            // invalidates only this addition.
+        }
+    }
+}
+
 [[nodiscard]] std::chrono::sys_days recurrence_scan_end(
     const Event& event, const RecurrenceRule& rule, TimePoint query_end,
     const Projection& projection)
@@ -564,12 +625,10 @@ void append_event_occurrences(EventOccurrences& result, const Event& event,
         return;
     }
 
-    const bool recurring = event.recurrence.has_value();
-    if ((!recurring || !is_exception(event, event.start)) &&
-        overlaps(event.start, event.end, begin, end)) {
-        result.push_back({&event, event.start, event.end, 0});
-    }
-    if (!recurring || !valid_rule_shape(event, *event.recurrence)) {
+    const bool recurring = is_recurring(event);
+    append_occurrence(result, event, event.start, event.end, 0U, begin, end,
+                      recurring);
+    if (!recurring) {
         return;
     }
 
@@ -578,20 +637,27 @@ void append_event_occurrences(EventOccurrences& result, const Event& event,
         if (projection.end < projection.start) {
             return;
         }
-        switch (event.recurrence->frequency) {
-        case RecurrenceFrequency::daily:
-            expand_daily(result, event, *event.recurrence, projection, begin, end);
-            break;
-        case RecurrenceFrequency::weekly:
-            expand_weekly(result, event, *event.recurrence, projection, begin, end);
-            break;
-        case RecurrenceFrequency::monthly:
-            expand_monthly(result, event, *event.recurrence, projection, begin, end);
-            break;
-        case RecurrenceFrequency::yearly:
-            expand_yearly(result, event, *event.recurrence, projection, begin, end);
-            break;
+        if (event.recurrence && valid_rule_shape(event, *event.recurrence)) {
+            switch (event.recurrence->frequency) {
+            case RecurrenceFrequency::daily:
+                expand_daily(result, event, *event.recurrence, projection, begin,
+                             end);
+                break;
+            case RecurrenceFrequency::weekly:
+                expand_weekly(result, event, *event.recurrence, projection, begin,
+                              end);
+                break;
+            case RecurrenceFrequency::monthly:
+                expand_monthly(result, event, *event.recurrence, projection,
+                               begin, end);
+                break;
+            case RecurrenceFrequency::yearly:
+                expand_yearly(result, event, *event.recurrence, projection, begin,
+                              end);
+                break;
+            }
         }
+        append_recurrence_additions(result, event, projection, begin, end);
     } catch (const std::exception&) {
         // Invalid zones and out-of-range civil projections retain DTSTART only.
     }

src/storage/ics_store.cpp

@@ -51,6 +51,7 @@ struct PendingEvent {
     std::optional<ParsedTime> start;
     std::optional<ParsedTime> end;
     std::vector<PendingProperty> recurrence_rules;
+    std::vector<PendingProperty> recurrence_dates;
     std::vector<PendingProperty> exception_dates;
 };
 
@@ -724,6 +725,15 @@ void serialize_calendar(std::ostream& output, std::span<const Event> events) {
         if (event.recurrence) {
             write_folded(output, "RRULE:" + serialize_recurrence_rule(event, *event.recurrence));
         }
+        if (!event.recurrence_additions.empty()) {
+            const std::string parameters = time_property_parameters(event);
+            const std::string values = join_values(event.recurrence_additions,
+                [&event](TimePoint addition) {
+                    return event.all_day ? format_date(addition)
+                        : format_event_time(event, addition);
+                });
+            write_folded(output, "RDATE" + parameters + ":" + values);
+        }
         if (!event.recurrence_exceptions.empty()) {
             const std::string parameters = time_property_parameters(event);
             const std::string values = join_values(event.recurrence_exceptions,
@@ -1056,9 +1066,17 @@ void validate_event_for_save(const Event& event) {
         throw std::invalid_argument(
             "cannot save event '" + event.uid + "' with an invalid interval");
     }
-    if (!event.recurrence && !event.recurrence_exceptions.empty()) {
+    if (!is_recurring(event) && !event.recurrence_exceptions.empty()) {
         throw std::invalid_argument(
-            "cannot save event '" + event.uid + "' with EXDATE values but no recurrence rule");
+            "cannot save event '" + event.uid
+            + "' with EXDATE values but no recurrence set");
+    }
+    std::vector<TimePoint> unique_additions = event.recurrence_additions;
+    std::sort(unique_additions.begin(), unique_additions.end());
+    if (std::adjacent_find(unique_additions.begin(), unique_additions.end())
+        != unique_additions.end()) {
+        throw std::invalid_argument(
+            "cannot save event '" + event.uid + "' with duplicate RDATE values");
     }
     std::vector<TimePoint> unique_exceptions = event.recurrence_exceptions;
     std::sort(unique_exceptions.begin(), unique_exceptions.end());
@@ -1221,6 +1239,29 @@ LoadResult IcsStore::load(const std::filesystem::path& path) {
                             }
                         }
                     }
+                    for (const PendingProperty& property : pending->recurrence_dates) {
+                        for (const std::string_view addition_value : split(property.value, ',')) {
+                            std::string warning;
+                            const auto parsed = parse_time(
+                                property.parameters, addition_value, warning);
+                            if (!parsed || !same_time_kind(*pending->start, *parsed)) {
+                                add_warning(result, property.line, parsed
+                                    ? "RDATE value type, time basis, or TZID does not match DTSTART"
+                                    : std::move(warning));
+                                mark_unsafe_to_rewrite(result);
+                                continue;
+                            }
+                            if (!warning.empty()) {
+                                add_warning(result, property.line, std::move(warning));
+                                mark_unsafe_to_rewrite(result);
+                            }
+                            if (std::find(event.recurrence_additions.begin(),
+                                    event.recurrence_additions.end(), parsed->value)
+                                == event.recurrence_additions.end()) {
+                                event.recurrence_additions.push_back(parsed->value);
+                            }
+                        }
+                    }
                     for (const PendingProperty& property : pending->exception_dates) {
                         for (const std::string_view exception_value : split(property.value, ',')) {
                             std::string warning;
@@ -1244,9 +1285,9 @@ LoadResult IcsStore::load(const std::filesystem::path& path) {
                             }
                         }
                     }
-                    if (!event.recurrence && !event.recurrence_exceptions.empty()) {
+                    if (!is_recurring(event) && !event.recurrence_exceptions.empty()) {
                         add_warning(result, event_start_line,
-                            "EXDATE without a supported RRULE cannot be edited safely");
+                            "EXDATE without a supported RRULE or RDATE cannot be edited safely");
                         mark_unsafe_to_rewrite(result);
                     }
                     result.events.push_back(std::move(event));
@@ -1275,7 +1316,7 @@ LoadResult IcsStore::load(const std::filesystem::path& path) {
             continue;
         }
         const bool time_property = name == "DTSTART" || name == "DTEND"
-            || name == "EXDATE";
+            || name == "RDATE" || name == "EXDATE";
         const bool recurrence_property = name == "RRULE";
         const bool text_property = name == "UID" || name == "SUMMARY" || name == "LOCATION"
             || name == "DESCRIPTION" || name == "X-NOCAL-CALENDAR-ID"
@@ -1305,6 +1346,9 @@ LoadResult IcsStore::load(const std::filesystem::path& path) {
         } else if (name == "RRULE") {
             pending->recurrence_rules.push_back(PendingProperty{
                 std::string(parameters), std::string(value), index + 1});
+        } else if (name == "RDATE") {
+            pending->recurrence_dates.push_back(PendingProperty{
+                std::string(parameters), std::string(value), index + 1});
         } else if (name == "EXDATE") {
             pending->exception_dates.push_back(PendingProperty{
                 std::string(parameters), std::string(value), index + 1});

src/tui/EventEditor.cpp

@@ -374,7 +374,7 @@ bool EventEditor::validate()
 
     Event candidate = original_;
     if (candidate.uid.empty()) candidate.uid = make_uid();
-    if (candidate.recurrence && all_day_ != candidate.all_day) {
+    if (is_recurring(candidate) && all_day_ != candidate.all_day) {
         return fail(EditorField::all_day,
                     "Timed/all-day conversion is unavailable for recurring series.");
     }
@@ -435,7 +435,7 @@ std::string EventEditor::render(const int requested_width, const int requested_h
     std::vector<std::string> lines;
     lines.reserve(16);
     lines.push_back(top);
-    const auto heading = editing_ && original_.recurrence
+    const auto heading = editing_ && is_recurring(original_)
                            ? "  NOCAL · EDIT ENTIRE RECURRING SERIES"
                            : editing_ ? "  NOCAL · EDIT APPOINTMENT"
                                       : "  NOCAL · NEW APPOINTMENT";

src/tui/Screen.cpp

@@ -802,7 +802,7 @@ std::string occurrence_focus_id(const std::span<const Event> events,
                                 const EventOccurrence& occurrence) {
     const auto index = event_source_index(events, occurrence.source);
     auto identity = source_focus_id(events, index);
-    if (occurrence.source->recurrence) {
+    if (is_recurring(*occurrence.source)) {
         const auto tick = occurrence.start.time_since_epoch().count();
         identity += "@occ:" + std::to_string(tick);
     }
@@ -1040,7 +1040,7 @@ std::string render_month(const std::span<const Event> events,
                                               ? std::nullopt
                                               : std::optional{local_start.time_of_day},
                 .segment = segment,
-                .recurring = event.recurrence.has_value(),
+                .recurring = is_recurring(event),
                 .recurrence_summary = event.recurrence
                                           ? recurrence_summary(*event.recurrence) : std::string{},
                 .source_time_zone = event.time_basis == TimeBasis::zoned

src/tui/TuiApp.cpp

@@ -233,7 +233,7 @@ void TuiApp::refresh_agenda() {
             .all_day = occurrence.source->all_day || continuation,
             .location = occurrence.source->location,
             .calendar_id = occurrence.source->calendar_id,
-            .recurring = occurrence.source->recurrence.has_value(),
+            .recurring = is_recurring(*occurrence.source),
         });
     }
     std::stable_sort(state_.agenda_items.begin(), state_.agenda_items.end(),
@@ -463,7 +463,7 @@ void TuiApp::submit_editor() {
                           std::span<const Calendar>{calendars_})) {
         state_.focused_event_id.reset();
         state_.show_event_details = false;
-        record_mutation(editing && events_[changed_index].recurrence
+        record_mutation(editing && is_recurring(events_[changed_index])
                             ? "edit recurring series"
                             : editing ? "edit appointment" : "add appointment");
         set_notification(std::move(success));
@@ -489,10 +489,10 @@ void TuiApp::submit_editor() {
                                     : std::optional{occurrence_focus_id(event_span, *first)};
     }
     state_.show_event_details = false;
-    record_mutation(editing && events_[changed_index].recurrence
+    record_mutation(editing && is_recurring(events_[changed_index])
                         ? "edit recurring series"
                         : editing ? "edit appointment" : "add appointment");
-    if (editing && events_[changed_index].recurrence) {
+    if (editing && is_recurring(events_[changed_index])) {
         success = "Recurring series updated.";
     }
     set_notification(std::move(success));
@@ -509,7 +509,7 @@ void TuiApp::confirm_delete() {
 
     auto original = events_;
     const auto original_focus = state_.focused_event_id;
-    const bool recurring = events_[*index].recurrence.has_value();
+    const bool recurring = is_recurring(events_[*index]);
     events_.erase(events_.begin() + static_cast<std::ptrdiff_t>(*index));
     if (!persist(std::span<const Event>{events_})) {
         events_.swap(original);
@@ -574,7 +574,7 @@ void TuiApp::submit_search() {
                                    : std::optional{local_time_of_day(occurrence.start)},
                 .all_day = occurrence.source->all_day,
                 .location = occurrence.source->location,
-                .recurring = occurrence.source->recurrence.has_value(),
+                .recurring = is_recurring(*occurrence.source),
             });
         }
         std::stable_sort(state_.search_results.begin(), state_.search_results.end(),

tests/calendar_transfer_tests.cpp

@@ -65,6 +65,7 @@ void check_invalid_argument(Function&& function, const std::string_view message)
     recurrence.by_month_day = {1, -1};
     recurrence.by_month = {1, 7};
     event.recurrence = std::move(recurrence);
+    event.recurrence_additions = {at(20)};
     event.recurrence_exceptions = {at(16), at(18)};
     return event;
 }
@@ -79,6 +80,7 @@ void check_invalid_argument(Function&& function, const std::string_view message)
            left.time_basis == right.time_basis &&
            left.time_zone == right.time_zone &&
            left.recurrence == right.recurrence &&
+           left.recurrence_additions == right.recurrence_additions &&
            left.recurrence_exceptions == right.recurrence_exceptions;
 }
 
@@ -163,6 +165,8 @@ void test_every_event_field_participates_in_collision_equality()
         {"time basis", [](auto& event) { event.time_basis = nocal::TimeBasis::utc; }},
         {"time zone", [](auto& event) { event.time_zone = "America/New_York"; }},
         {"recurrence", [](auto& event) { event.recurrence->interval += 1; }},
+        {"recurrence additions",
+         [](auto& event) { event.recurrence_additions.push_back(at(19)); }},
         {"recurrence exclusions",
          [](auto& event) { event.recurrence_exceptions.push_back(at(19)); }},
     };

tests/domain_tests.cpp

@@ -404,6 +404,90 @@ void test_weekly_count_and_exdates()
           "weekly BYDAY expansion is chronological across week boundaries");
 }
 
+void test_rdate_only_query_boundaries_and_duration()
+{
+    using namespace std::chrono;
+    const nocal::Date july_10{2026y / July / 10d};
+    const nocal::Date july_11{2026y / July / 11d};
+    nocal::Event added;
+    added.uid = "rdate-only";
+    added.title = added.uid;
+    added.start = utc_time(2026y / July / 1d, 9);
+    added.end = added.start + minutes{90};
+    added.recurrence_additions = {utc_time(july_10, 9),
+                                  utc_time(july_11, 9)};
+
+    check(nocal::is_recurring(added),
+          "an RDATE-only event is part of a recurrence set");
+    const std::vector<nocal::Event> events{added};
+    const auto occurrences = nocal::occurrences_overlapping(
+        events, utc_time(july_10, 10), utc_time(july_11, 9));
+    check(occurrences.size() == 1 &&
+              occurrences.front().start == utc_time(july_10, 9),
+          "RDATE overlap includes a carrying occurrence and excludes a start at the query end");
+    check(occurrences.size() == 1 &&
+              occurrences.front().end == utc_time(july_10, 10, 30),
+          "UTC RDATE occurrences preserve DTSTART's elapsed duration");
+}
+
+void test_rdate_merge_deduplication_and_exdates()
+{
+    using namespace std::chrono;
+    const nocal::Date july_1{2026y / July / 1d};
+    nocal::RecurrenceRule daily;
+    daily.frequency = nocal::RecurrenceFrequency::daily;
+    daily.count = 3U;
+    auto merged = utc_recurring("rdate-merge", july_1, 9, july_1, 10, daily);
+    merged.recurrence_additions = {
+        merged.start, utc_time(2026y / July / 2d, 9),
+        utc_time(2026y / July / 4d, 9), utc_time(2026y / July / 4d, 9)};
+
+    const auto all = nocal::occurrences_overlapping(
+        std::span<const nocal::Event>{&merged, 1}, utc_time(july_1, 0),
+        utc_time(2026y / July / 5d, 0));
+    check(all.size() == 4,
+          "DTSTART, RRULE, and RDATE form a set with duplicate starts collapsed");
+    check(all.size() == 4 && all[0].ordinal == 0U && all[1].ordinal == 1U &&
+              all[2].ordinal == 2U &&
+              all[3].start == utc_time(2026y / July / 4d, 9),
+          "RDATE merging preserves existing RRULE ordinals");
+
+    merged.recurrence_exceptions = {merged.start,
+                                    utc_time(2026y / July / 4d, 9)};
+    const auto filtered = nocal::occurrences_overlapping(
+        std::span<const nocal::Event>{&merged, 1}, utc_time(july_1, 0),
+        utc_time(2026y / July / 5d, 0));
+    check(filtered.size() == 2 &&
+              filtered[0].start == utc_time(2026y / July / 2d, 9) &&
+              filtered[1].start == utc_time(2026y / July / 3d, 9),
+          "EXDATE subtracts both DTSTART and RDATE-only starts from the recurrence set");
+}
+
+void test_zoned_rdate_wall_duration()
+{
+    using namespace std::chrono;
+    nocal::Event added;
+    added.uid = "zoned-rdate";
+    added.title = added.uid;
+    added.time_basis = nocal::TimeBasis::zoned;
+    added.time_zone = "Europe/London";
+    added.start = zoned_time(added.time_zone, 2026y / March / 28d, 0, 30);
+    added.end = zoned_time(added.time_zone, 2026y / March / 28d, 2, 30);
+    added.recurrence_additions = {
+        zoned_time(added.time_zone, 2026y / March / 29d, 0, 30)};
+
+    const auto occurrences = nocal::occurrences_overlapping(
+        std::span<const nocal::Event>{&added, 1},
+        utc_time(2026y / March / 29d, 0), utc_time(2026y / March / 30d, 0));
+    check(occurrences.size() == 1 &&
+              occurrences[0].start == utc_time(2026y / March / 29d, 0, 30) &&
+              occurrences[0].end == utc_time(2026y / March / 29d, 1, 30),
+          "zoned RDATE preserves a two-hour wall duration across the DST gap");
+    check(occurrences.size() == 1 &&
+              occurrences[0].end - occurrences[0].start == hours{1},
+          "zoned RDATE projects its wall-clock end through the DST transition");
+}
+
 void test_monthly_and_yearly_selectors()
 {
     using namespace std::chrono;
@@ -482,6 +566,14 @@ void test_occurrence_overlap_sorting_and_invalid_rules()
               occurrences[3].source->uid == "later",
           "equal occurrence times sort by title and UID");
 
+    invalid.recurrence_additions = {utc_time(day, 15)};
+    const auto invalid_rule_addition = nocal::occurrences_overlapping(
+        std::span<const nocal::Event>{&invalid, 1}, utc_time(day, 0),
+        utc_time(2026y / July / 18d, 0));
+    check(invalid_rule_addition.size() == 2 &&
+              invalid_rule_addition[1].start == utc_time(day, 15),
+          "a malformed RRULE does not suppress an independently valid RDATE");
+
     invalid.time_basis = nocal::TimeBasis::zoned;
     invalid.time_zone = "Not/A_Real_Zone";
     invalid.recurrence->interval = 1U;
@@ -504,6 +596,9 @@ int main()
     test_daily_dst_recurrence();
     test_floating_dst_and_until();
     test_weekly_count_and_exdates();
+    test_rdate_only_query_boundaries_and_duration();
+    test_rdate_merge_deduplication_and_exdates();
+    test_zoned_rdate_wall_duration();
     test_monthly_and_yearly_selectors();
     test_occurrence_overlap_sorting_and_invalid_rules();
     if (failures != 0) {

tests/editor_tests.cpp

@@ -246,6 +246,8 @@ void test_zoned_edit_preserves_series_and_rejects_dst_gap()
     };
     event.recurrence_exceptions.push_back(
         zoned_time(event.time_zone, nocal::Date{2026y / March / 9d}, 2, 30));
+    event.recurrence_additions.push_back(
+        zoned_time(event.time_zone, nocal::Date{2026y / March / 12d}, 2, 30));
 
     nocal::tui::EventEditor editor{event};
     check(editor.field_value(nocal::tui::EditorField::start_date) == "2026-03-07" &&
@@ -262,8 +264,9 @@ void test_zoned_edit_preserves_series_and_rejects_dst_gap()
     check(editor.result().time_basis == nocal::TimeBasis::zoned &&
               editor.result().time_zone == "America/New_York" &&
               editor.result().recurrence == event.recurrence &&
+              editor.result().recurrence_additions == event.recurrence_additions &&
               editor.result().recurrence_exceptions == event.recurrence_exceptions,
-          "editing preserves time basis, TZID, recurrence, and exceptions");
+          "editing preserves time basis, TZID, recurrence additions, and exceptions");
 
     nocal::tui::EventEditor series_kind_editor{event};
     focus(series_kind_editor, nocal::tui::EditorField::all_day);
@@ -273,8 +276,21 @@ void test_zoned_edit_preserves_series_and_rejects_dst_gap()
               series_kind_editor.error().find("recurring series") != std::string_view::npos,
           "a recurring series rejects timed/all-day conversion to preserve its exceptions");
 
+    auto rdate_only = event;
+    rdate_only.recurrence.reset();
+    nocal::tui::EventEditor rdate_editor{rdate_only};
+    check(rdate_editor.render(80, 18, false).find("EDIT ENTIRE RECURRING SERIES")
+              != std::string::npos,
+          "an RDATE-only event is presented as a recurring series");
+    focus(rdate_editor, nocal::tui::EditorField::all_day);
+    (void)rdate_editor.handle_key(" ");
+    check(rdate_editor.handle_key("\x13") == nocal::tui::EditorOutcome::active &&
+              rdate_editor.error().find("recurring series") != std::string_view::npos,
+          "an RDATE-only series rejects timed/all-day conversion");
+
     auto one_off = event;
     one_off.recurrence.reset();
+    one_off.recurrence_additions.clear();
     one_off.recurrence_exceptions.clear();
     nocal::tui::EventEditor all_day_editor{one_off};
     focus(all_day_editor, nocal::tui::EditorField::all_day);

tests/ics_tests.cpp

@@ -473,6 +473,8 @@ void test_time_basis_round_trips_and_dst(const std::filesystem::path& root) {
                 && reloaded.events[index].time_basis == loaded.events[index].time_basis
                 && reloaded.events[index].time_zone == loaded.events[index].time_zone
                 && reloaded.events[index].recurrence == loaded.events[index].recurrence
+                && reloaded.events[index].recurrence_additions
+                    == loaded.events[index].recurrence_additions
                 && reloaded.events[index].recurrence_exceptions
                     == loaded.events[index].recurrence_exceptions,
             "time-basis semantic round trip differs");
@@ -541,12 +543,115 @@ void test_supported_recurrence_and_exdates(const std::filesystem::path& root) {
         "recurrence semantic round-trip event count differs");
     for (std::size_t index = 0; index < loaded.events.size(); ++index) {
         require(reloaded.events[index].recurrence == loaded.events[index].recurrence
+                && reloaded.events[index].recurrence_additions
+                    == loaded.events[index].recurrence_additions
                 && reloaded.events[index].recurrence_exceptions
                     == loaded.events[index].recurrence_exceptions,
             "recurrence semantic round trip differs");
     }
 }
 
+void test_supported_rdates(const std::filesystem::path& root) {
+    const auto path = root / "rdates.ics";
+    write_fixture(path,
+        "BEGIN:VCALENDAR\r\nVERSION:2.0\r\n"
+        "BEGIN:VEVENT\r\nUID:utc-rdate\r\nSUMMARY:UTC additions\r\n"
+        "DTSTART:20260717T090000Z\r\nDTEND:20260717T100000Z\r\n"
+        "RDATE:20260718T090000Z,20260720T090000Z\r\n"
+        "RDATE:20260722T090000Z\r\nEXDATE:20260720T090000Z\r\nEND:VEVENT\r\n"
+        "BEGIN:VEVENT\r\nUID:floating-rdate\r\nSUMMARY:Floating additions\r\n"
+        "DTSTART:20260717T101500\r\nDTEND:20260717T111500\r\n"
+        "RDATE:20260718T101500,20260719T101500\r\nEND:VEVENT\r\n"
+        "BEGIN:VEVENT\r\nUID:zoned-rdate\r\nSUMMARY:Zoned additions\r\n"
+        "DTSTART;TZID=Europe/London:20260717T101500\r\n"
+        "DTEND;TZID=Europe/London:20260717T111500\r\n"
+        "RDATE;TZID=Europe/London:20260718T101500,20260719T101500\r\nEND:VEVENT\r\n"
+        "BEGIN:VEVENT\r\nUID:all-day-rdate\r\nSUMMARY:All-day additions\r\n"
+        "DTSTART;VALUE=DATE:20260717\r\nDTEND;VALUE=DATE:20260718\r\n"
+        "RDATE;VALUE=DATE:20260719,20260721\r\nEND:VEVENT\r\n"
+        "BEGIN:VEVENT\r\nUID:mixed-rdate\r\nSUMMARY:Rule and additions\r\n"
+        "DTSTART:20260717T090000Z\r\nDTEND:20260717T100000Z\r\n"
+        "RRULE:FREQ=DAILY;COUNT=3\r\nRDATE:20260725T090000Z,20260727T090000Z\r\n"
+        "EXDATE:20260718T090000Z,20260725T090000Z\r\nEND:VEVENT\r\n"
+        "END:VCALENDAR\r\n");
+
+    const auto loaded = nocal::storage::IcsStore::load(path);
+    require(loaded.safe_to_rewrite && loaded.warnings.empty(),
+        "supported RDATE values were not rewrite-safe");
+    require(loaded.events.size() == 5, "RDATE fixture event count differs");
+    require(!loaded.events[0].recurrence.has_value(),
+        "RDATE-only event acquired an RRULE");
+    require(loaded.events[0].recurrence_additions
+            == std::vector<nocal::TimePoint>{
+                sys_days{year{2026}/July/18} + 9h,
+                sys_days{year{2026}/July/20} + 9h,
+                sys_days{year{2026}/July/22} + 9h},
+        "multiple or comma-separated UTC RDATE values were not collected");
+    require(loaded.events[0].recurrence_exceptions
+            == std::vector<nocal::TimePoint>{sys_days{year{2026}/July/20} + 9h},
+        "RDATE-only EXDATE value was not retained");
+    require(loaded.events[1].time_basis == nocal::TimeBasis::floating
+            && loaded.events[1].recurrence_additions
+                == std::vector<nocal::TimePoint>{
+                    sys_days{year{2026}/July/18} + 10h + 15min,
+                    sys_days{year{2026}/July/19} + 10h + 15min},
+        "floating RDATE values did not preserve their time basis");
+    require(loaded.events[2].time_basis == nocal::TimeBasis::zoned
+            && loaded.events[2].time_zone == "Europe/London"
+            && loaded.events[2].recurrence_additions
+                == std::vector<nocal::TimePoint>{
+                    sys_days{year{2026}/July/18} + 9h + 15min,
+                    sys_days{year{2026}/July/19} + 9h + 15min},
+        "zoned RDATE values were not converted with DTSTART's TZID");
+    require(loaded.events[3].all_day
+            && loaded.events[3].recurrence_additions
+                == std::vector<nocal::TimePoint>{
+                    sys_days{year{2026}/July/19}, sys_days{year{2026}/July/21}},
+        "all-day RDATE values were not parsed as DATE values");
+    require(loaded.events[4].recurrence.has_value()
+            && loaded.events[4].recurrence_additions
+                == std::vector<nocal::TimePoint>{
+                    sys_days{year{2026}/July/25} + 9h,
+                    sys_days{year{2026}/July/27} + 9h}
+            && loaded.events[4].recurrence_exceptions
+                == std::vector<nocal::TimePoint>{
+                    sys_days{year{2026}/July/18} + 9h,
+                    sys_days{year{2026}/July/25} + 9h},
+        "mixed RRULE, RDATE, and EXDATE values differ");
+
+    const auto round_trip = root / "rdates-round-trip.ics";
+    nocal::storage::IcsStore::save(round_trip, loaded.events);
+    const std::string serialized = read_fixture(round_trip);
+    require(serialized.find(
+            "RDATE:20260718T090000Z,20260720T090000Z,20260722T090000Z")
+            != std::string::npos,
+        "UTC RDATE values were not grouped on serialization");
+    require(serialized.find("RDATE:20260718T101500,20260719T101500")
+            != std::string::npos,
+        "floating RDATE values were not serialized without a suffix");
+    require(serialized.find(
+            "RDATE;TZID=Europe/London:20260718T101500,20260719T101500")
+            != std::string::npos,
+        "zoned RDATE values were not serialized with TZID");
+    require(serialized.find("RDATE;VALUE=DATE:20260719,20260721")
+            != std::string::npos,
+        "all-day RDATE values were not serialized with VALUE=DATE");
+
+    const auto reloaded = nocal::storage::IcsStore::load(round_trip);
+    require(reloaded.safe_to_rewrite && reloaded.warnings.empty(),
+        "serialized RDATE calendar did not reload safely");
+    require(reloaded.events.size() == loaded.events.size(),
+        "RDATE semantic round-trip event count differs");
+    for (std::size_t index = 0; index < loaded.events.size(); ++index) {
+        require(reloaded.events[index].recurrence == loaded.events[index].recurrence
+                && reloaded.events[index].recurrence_additions
+                    == loaded.events[index].recurrence_additions
+                && reloaded.events[index].recurrence_exceptions
+                    == loaded.events[index].recurrence_exceptions,
+            "RDATE semantic round trip differs");
+    }
+}
+
 void test_unsupported_recurrence_and_zones_are_unsafe(const std::filesystem::path& root) {
     const std::vector<std::string> unsupported_properties{
         "RRULE:FREQ=WEEKLY;BYDAY=1MO",
@@ -554,7 +659,7 @@ void test_unsupported_recurrence_and_zones_are_unsafe(const std::filesystem::pat
         "RRULE:FREQ=DAILY;COUNT=2;UNTIL=20260720T090000Z",
         "RRULE:FREQ=HOURLY",
         "RRULE:FREQ=DAILY;WKST=MO",
-        "RDATE:20260718T090000Z",
+        "RDATE;VALUE=PERIOD:20260718T090000Z/PT1H",
         "RECURRENCE-ID:20260718T090000Z"};
     for (std::size_t index = 0; index < unsupported_properties.size(); ++index) {
         const auto path = root / ("unsupported-rule-" + std::to_string(index) + ".ics");
@@ -595,6 +700,37 @@ void test_unsupported_recurrence_and_zones_are_unsafe(const std::filesystem::pat
     require(!nocal::storage::IcsStore::load(custom_zone).safe_to_rewrite,
         "VTIMEZONE definition was considered rewrite-safe");
 
+    struct InvalidRdate {
+        std::string start;
+        std::string end;
+        std::string property;
+    };
+    const std::vector<InvalidRdate> invalid_rdates{
+        {"DTSTART:20260717T090000Z", "DTEND:20260717T100000Z",
+            "RDATE:20260718T090000"},
+        {"DTSTART;TZID=Europe/London:20260717T090000",
+            "DTEND;TZID=Europe/London:20260717T100000",
+            "RDATE;TZID=Europe/Paris:20260718T090000"},
+        {"DTSTART;VALUE=DATE:20260717", "DTEND;VALUE=DATE:20260718",
+            "RDATE:20260719T090000Z"},
+        {"DTSTART:20260717T090000Z", "DTEND:20260717T100000Z",
+            "RDATE;TZID=Custom/Mars:20260718T090000"},
+        {"DTSTART:20260717T090000Z", "DTEND:20260717T100000Z",
+            "RDATE:not-a-date"}};
+    for (std::size_t index = 0; index < invalid_rdates.size(); ++index) {
+        const auto path = root / ("invalid-rdate-" + std::to_string(index) + ".ics");
+        const auto& fixture = invalid_rdates[index];
+        write_fixture(path,
+            "BEGIN:VCALENDAR\r\nVERSION:2.0\r\nBEGIN:VEVENT\r\nUID:invalid-rdate\r\n"
+            + fixture.start + "\r\n" + fixture.end + "\r\n" + fixture.property
+            + "\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n");
+        const auto loaded = nocal::storage::IcsStore::load(path);
+        require(!loaded.safe_to_rewrite && !loaded.warnings.empty(),
+            "invalid RDATE was considered rewrite-safe");
+        require(loaded.events.size() == 1 && loaded.events[0].recurrence_additions.empty(),
+            "invalid RDATE prevented base-event browsing or became an occurrence");
+    }
+
     const std::vector<std::pair<std::string, std::string>> mismatched_ends{
         {"DTSTART:20260717T090000Z", "DTEND:20260717T100000"},
         {"DTSTART;TZID=Europe/London:20260717T090000",
@@ -660,7 +796,20 @@ void test_save_validation_preserves_existing_bytes(const std::filesystem::path&
     }
     require(exdate_failed && read_fixture(path) == original
             && read_fixture(backup) == original_backup,
-        "EXDATE-without-RRULE validation changed calendar or backup bytes");
+        "EXDATE-without-RRULE-or-RDATE validation changed calendar or backup bytes");
+
+    nocal::Event duplicate_rdate = event_named("rdate@example.test", "Duplicate RDATE");
+    duplicate_rdate.recurrence_additions = {
+        duplicate_rdate.start + 24h, duplicate_rdate.start + 24h};
+    bool rdate_failed = false;
+    try {
+        nocal::storage::IcsStore::save(path, std::vector<nocal::Event>{duplicate_rdate});
+    } catch (const std::invalid_argument&) {
+        rdate_failed = true;
+    }
+    require(rdate_failed && read_fixture(path) == original
+            && read_fixture(backup) == original_backup,
+        "duplicate RDATE validation changed calendar or backup bytes");
     require_no_temporary_files(path);
 }
 
@@ -691,6 +840,7 @@ int main() {
         test_unsupported_data_is_not_rewrite_safe(root);
         test_time_basis_round_trips_and_dst(root);
         test_supported_recurrence_and_exdates(root);
+        test_supported_rdates(root);
         test_unsupported_recurrence_and_zones_are_unsafe(root);
         test_save_validation_preserves_existing_bytes(root);
         std::filesystem::remove_all(root, ignored);

tests/tui_focus_tests.cpp

@@ -72,6 +72,7 @@ bool same_event(const nocal::Event& left, const nocal::Event& right)
            left.calendar_id == right.calendar_id && left.color == right.color &&
            left.time_basis == right.time_basis && left.time_zone == right.time_zone &&
            left.recurrence == right.recurrence &&
+           left.recurrence_additions == right.recurrence_additions &&
            left.recurrence_exceptions == right.recurrence_exceptions;
 }
 
@@ -819,6 +820,36 @@ void test_recurring_occurrence_navigation_and_whole_series_crud()
           "undo restores a deleted recurring series");
 }
 
+void test_rdate_only_occurrence_identity_and_whole_series_crud()
+{
+    using namespace std::chrono;
+    const auto selected = nocal::today();
+    const auto previous = nocal::from_sys_days(nocal::to_sys_days(selected) - days{1});
+    auto series = make_event("rdate-only", "Extra date", previous, 9, 0,
+                             previous, 10, 0);
+    series.recurrence_additions = {
+        nocal::make_local_time(selected, 9, 0),
+    };
+    std::vector<nocal::Event> events{series};
+    nocal::tui::TuiApp app{events, -1, -1};
+
+    app.dispatch(nocal::tui::Action::next_event);
+    check(focus_starts_with(app, "rdate-only@occ:"),
+          "an RDATE-only occurrence has a source-and-start focus identity");
+    app.dispatch(nocal::tui::Action::edit_event);
+    replace_editor_title(app, "Edited extra-date series");
+    app.handle_input("\x13");
+    check(events.front().title == "Edited extra-date series" &&
+              events.front().recurrence_additions == series.recurrence_additions &&
+              app.state().notification == "Recurring series updated.",
+          "editing an RDATE-only occurrence updates and preserves the whole series");
+
+    app.dispatch(nocal::tui::Action::delete_event);
+    app.handle_input("y");
+    check(events.empty() && app.state().notification == "Recurring series deleted.",
+          "deleting an RDATE-only occurrence removes its entire source series");
+}
+
 void test_recurrence_grid_expansion_and_source_zone_display()
 {
     using namespace std::chrono;
@@ -1241,6 +1272,7 @@ int main()
     test_narrow_detail_wrapping_without_ansi();
     test_multiday_segment_labels_and_series_messaging();
     test_recurring_occurrence_navigation_and_whole_series_crud();
+    test_rdate_only_occurrence_identity_and_whole_series_crud();
     test_recurrence_grid_expansion_and_source_zone_display();
     test_search_prompt_results_and_occurrence_jump();
     test_calendar_visibility_filters_without_partial_saves();