Pin the behaviour of an aggregate with no sink

An aggregate without a default_sink leaves events created in it alone, which is
how a target calendar keeps events of its own. The reconciler unit tests cover
the decision; this covers it surviving the round trip, and specifically that it
holds on every subsequent cycle — an event that survived the first cycle and
was swept up by the second would be worse than never having worked.

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

tests/caldav.rs

@@ -23,6 +23,12 @@ const MEETING: &str = "BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//test//EN\r\n\
      BEGIN:VALARM\r\nACTION:DISPLAY\r\nTRIGGER:-PT15M\r\nDESCRIPTION:Soon\r\n\
      END:VALARM\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n";
 
+/// An event written straight into the aggregate, belonging to no source.
+const HAND_WRITTEN: &str = "BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//phone//EN\r\n\
+     BEGIN:VEVENT\r\nUID:hand-written@phone\r\nDTSTAMP:20260101T000000Z\r\n\
+     DTSTART:20260911T140000Z\r\nDTEND:20260911T150000Z\r\nSUMMARY:Dentist\r\n\
+     END:VEVENT\r\nEND:VCALENDAR\r\n";
+
 const HOLIDAY_FEED: &str = "BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//feed//EN\r\n\
      BEGIN:VEVENT\r\nUID:newyear@feed\r\nDTSTAMP:20260101T000000Z\r\n\
      DTSTART;VALUE=DATE:20260101\r\nDTEND;VALUE=DATE:20260102\r\n\
@@ -272,3 +278,54 @@ fn a_retired_endpoints_mirror_is_reported_and_then_removed() {
     assert!(removed.succeeded(), "{}", removed.stderr);
     assert!(!mirror.exists(), "the orphaned mirror should be gone");
 }
+
+/// An aggregate with no `default_sink` leaves events created in it alone.
+///
+/// This is how a target calendar keeps events of its own: with nowhere
+/// configured to file a new event, calcalist refuses to guess rather than
+/// picking a source, so the event simply stays where it was written. Worth
+/// pinning, because "left alone" has to hold on every subsequent cycle too —
+/// an event that survived the first one and was swept up by the second would
+/// be worse than never having worked.
+#[test]
+fn an_event_created_in_a_sinkless_aggregate_stays_where_it_is() {
+    let Some(fixture) = fixture() else { return };
+
+    // The fixture's aggregate has a default_sink; take it away.
+    let sinkless = std::fs::read_to_string(&fixture.calcalist.config)
+        .expect("read config")
+        .replace("default_sink = \"work\"\n", "");
+    std::fs::write(&fixture.calcalist.config, sinkless).expect("rewrite config");
+
+    assert!(fixture.calcalist.run(&["sync"]).succeeded());
+
+    // Now add an event by hand, as a calendar app would.
+    fixture
+        .server
+        .put_event("unified", "dentist.ics", HAND_WRITTEN);
+
+    for cycle in 1..=3 {
+        let run = fixture.calcalist.run(&["sync"]);
+        assert!(
+            run.succeeded(),
+            "cycle {cycle} failed\n{}\n{}",
+            run.stdout,
+            run.stderr
+        );
+
+        let published = fixture.server.stored("unified");
+        assert!(
+            published.iter().any(|item| item.contains("Dentist")),
+            "cycle {cycle}: the hand-written event was removed:\n{published:?}"
+        );
+        // It never reaches a source: there is nowhere it was told to go.
+        assert!(
+            !fixture
+                .server
+                .stored("work")
+                .iter()
+                .any(|item| item.contains("Dentist")),
+            "cycle {cycle}: the hand-written event leaked into the source"
+        );
+    }
+}