fix(importing): make document receivers/tags canonical-authoritative on re-import

The DocumentImporter accumulated receivers/tags via addAll without pruning, so a
shrunk canonical row left stale links on a re-imported PLACEHOLDER document. Clear
the collections before re-populating so the canonical row is authoritative: a removed
receiver/tag is now pruned. Raw sender_text/receiver_text retention is unchanged.

Refs #669

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

backend/src/main/java/org/raddatz/familienarchiv/importing/DocumentImporter.java

@@ -165,6 +165,10 @@ public class DocumentImporter {
         doc.setContentType(contentType);
         doc.setSender(sender);
         doc.setSenderText(blankToNull(senderName));
+        // The canonical row is authoritative for receivers/tags (ADR-025): clear then
+        // re-populate so a shrunk set on re-import prunes stale links rather than
+        // accumulating them. The raw sender_text/receiver_text retention is separate.
+        doc.getReceivers().clear();
         doc.getReceivers().addAll(receivers);
         doc.setReceiverText(blankToNull(receiverNames));
         doc.setDocumentDate(parseIsoDate(row.get("date_iso")));
@@ -203,7 +207,10 @@ public class DocumentImporter {
                         .build()));
     }
 
+    // Authoritative: the canonical row defines the document's tags exactly. Clearing first
+    // means a tag removed from the row is pruned on re-import (ADR-025).
     private void attachTag(Document doc, String tagPath) {
+        doc.getTags().clear();
         if (tagPath.isBlank()) return;
         tagService.findBySourceRef(tagPath).ifPresent(tag -> doc.getTags().add(tag));
     }

backend/src/test/java/org/raddatz/familienarchiv/importing/DocumentImporterTest.java

@@ -382,6 +382,28 @@ class DocumentImporterTest {
         verify(documentService).save(org.mockito.ArgumentMatchers.argThat(d -> d.getId().equals(existing.getId())));
     }
 
+    // ─── canonical collections are authoritative — re-import prunes removed links ──────
+
+    @Test
+    void load_prunesReceiversAndTags_whenCanonicalRowShrinks(@TempDir Path tempDir) throws Exception {
+        ReflectionTestUtils.setField(importer, "importDir", tempDir.toString());
+        Person staleReceiver = Person.builder().id(UUID.randomUUID()).sourceRef("stale-receiver").lastName("Stale").build();
+        Tag staleTag = Tag.builder().id(UUID.randomUUID()).name("Stale").sourceRef("Themen/Stale").build();
+        Document existing = Document.builder().id(UUID.randomUUID())
+                .originalFilename("W-0008").status(DocumentStatus.PLACEHOLDER).build();
+        existing.getReceivers().add(staleReceiver);
+        existing.getTags().add(staleTag);
+        when(documentService.findByOriginalFilename("W-0008")).thenReturn(Optional.of(existing));
+        when(documentService.save(any())).thenAnswer(inv -> inv.getArgument(0));
+        // The canonical row now carries no receiver and no tag: both stale links must go.
+        Path xlsx = writeDocs(tempDir, docRow("W-0008", "", "", "", "", "", "", "", "", ""));
+
+        importer.load(xlsx.toFile());
+
+        verify(documentService).save(org.mockito.ArgumentMatchers.argThat(d ->
+                d.getReceivers().isEmpty() && d.getTags().isEmpty()));
+    }
+
     // ─── helpers ─────────────────────────────────────────────────────────────────────
 
     private Map<String, String> docRow(String index, String file, String senderId, String senderName,