test(transcription): rename propagation across 200 blocks must stay under 2 seconds

Latency floor (Sara): a merge-blocking regression check, not a benchmark.
Seeds 200 blocks each with one mention of the same person, fires the rename,
and asserts the listener completes the entire find/mutate/saveAllAndFlush
cycle in less than two seconds against the Testcontainers Postgres.

Confirms the partial reload (one Auguste → Augusta) actually persisted so
the timing isn't measuring an empty path.

Refs #362

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/src/test/java/org/raddatz/familienarchiv/service/PersonMentionPropagationListenerTest.java

@@ -21,6 +21,7 @@ import org.springframework.boot.jdbc.test.autoconfigure.AutoConfigureTestDatabas
 import org.springframework.boot.data.jpa.test.autoconfigure.DataJpaTest;
 import org.springframework.context.annotation.Import;
 
+import java.util.ArrayList;
 import java.util.List;
 import java.util.UUID;
 
@@ -165,6 +166,37 @@ class PersonMentionPropagationListenerTest {
                 .containsExactly("Ghost Name");
     }
 
+    @Test
+    void propagatesAcross200Blocks_inUnderTwoSeconds_latencyFloor() {
+        UUID personId = savedPersonId("Auguste", "Raddatz");
+        List<UUID> blockIds = new ArrayList<>();
+        for (int i = 0; i < 200; i++) {
+            TranscriptionBlock saved = blockRepository.save(TranscriptionBlock.builder()
+                    .annotationId(annotationId).documentId(documentId)
+                    .text("Block " + i + " mentions @Auguste Raddatz here.")
+                    .sortOrder(i)
+                    .mentionedPersons(List.of(new PersonMention(personId, "Auguste Raddatz")))
+                    .build());
+            blockIds.add(saved.getId());
+        }
+        blockRepository.flush();
+        em.clear();
+
+        long start = System.nanoTime();
+        listener.onPersonDisplayNameChanged(
+                new PersonDisplayNameChangedEvent(personId, "Auguste Raddatz", "Augusta Raddatz"));
+        blockRepository.flush();
+        long elapsedMs = (System.nanoTime() - start) / 1_000_000;
+
+        assertThat(elapsedMs)
+                .as("Propagation across 200 blocks must stay under 2s — merge-blocking regression floor")
+                .isLessThan(2000L);
+
+        em.clear();
+        TranscriptionBlock first = blockRepository.findById(blockIds.get(0)).orElseThrow();
+        assertThat(first.getText()).contains("@Augusta Raddatz");
+    }
+
     @Test
     void leavesUnrelatedBlockUntouched_whenNoSidecarReferencesPerson() {
         UUID personId = savedPersonId("Auguste", "Raddatz");