feat(ocr): add Preprocessing NDJSON event to Java stream pipeline

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

@@ -230,6 +230,42 @@ class OcrAsyncRunnerTest {
         assertThat(job.getProgressMessage()).isEqualTo("DONE:0:1");
     }
 
+    @Test
+    void runSingleDocument_updatesProgressOnPreprocessingEvent() {
+        UUID jobId = UUID.randomUUID();
+        UUID docId = UUID.randomUUID();
+        UUID userId = UUID.randomUUID();
+        OcrJob job = OcrJob.builder().id(jobId).totalDocuments(1).status(OcrJobStatus.PENDING).build();
+        OcrJobDocument jobDoc = OcrJobDocument.builder().id(UUID.randomUUID())
+                .jobId(jobId).documentId(docId).status(OcrDocumentStatus.PENDING).build();
+        Document doc = Document.builder().id(docId).filePath("test.pdf")
+                .fileHash("hash").scriptType(ScriptType.TYPEWRITER).build();
+
+        when(ocrJobRepository.findById(jobId)).thenReturn(Optional.of(job));
+        when(ocrJobRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));
+        when(ocrJobDocumentRepository.findByJobIdAndDocumentId(jobId, docId))
+                .thenReturn(Optional.of(jobDoc));
+        when(ocrJobDocumentRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));
+        when(documentService.getDocumentById(docId)).thenReturn(doc);
+        when(fileService.generatePresignedUrl(any())).thenReturn("http://presigned");
+
+        List<String> progressMessages = new ArrayList<>();
+        doAnswer(inv -> {
+            Consumer<OcrStreamEvent> handler = inv.getArgument(3);
+            handler.accept(new OcrStreamEvent.Start(5));
+            handler.accept(new OcrStreamEvent.Preprocessing(1));
+            progressMessages.add(job.getProgressMessage());
+            handler.accept(new OcrStreamEvent.Page(1, List.of()));
+            handler.accept(new OcrStreamEvent.Done(0, 0));
+            return null;
+        }).when(ocrClient).streamBlocks(any(), any(), any(), any());
+
+        ocrAsyncRunner.runSingleDocument(jobId, docId, userId);
+
+        // Must have totalPages=5 from the preceding Start event, not 0
+        assertThat(progressMessages.get(0)).isEqualTo("PREPROCESSING_PAGE:1:5");
+    }
+
     @Test
     void runSingleDocument_logsStreamErrorAtWarnWithoutSettingJobFailed() {
         UUID jobId = UUID.randomUUID();

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

@@ -37,11 +37,19 @@ class OcrStreamEventTest {
         assertThat(done.skippedPages()).isEqualTo(2);
     }
 
+    @Test
+    void preprocessingRecordHoldsPageNumber() {
+        var preprocessing = new OcrStreamEvent.Preprocessing(4);
+        assertThat(preprocessing.pageNumber()).isEqualTo(4);
+        assertThat(preprocessing).isInstanceOf(OcrStreamEvent.class);
+    }
+
     @Test
     void patternMatchingWorksOnSealedInterface() {
         OcrStreamEvent event = new OcrStreamEvent.Start(3);
         String result = switch (event) {
             case OcrStreamEvent.Start s -> "start:" + s.totalPages();
+            case OcrStreamEvent.Preprocessing pre -> "preprocessing:" + pre.pageNumber();
             case OcrStreamEvent.Page p -> "page:" + p.pageNumber();
             case OcrStreamEvent.Error e -> "error:" + e.pageNumber();
             case OcrStreamEvent.Done d -> "done:" + d.totalBlocks();

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

@@ -83,6 +83,25 @@ class RestClientOcrClientStreamTest {
         assertThat(events).hasSize(3);
     }
 
+    @Test
+    void parseNdjsonStream_dispatchesPreprocessingEvent() {
+        String ndjson = """
+                {"type":"start","totalPages":3}
+                {"type":"preprocessing","pageNumber":1}
+                {"type":"page","pageNumber":1,"blocks":[]}
+                {"type":"done","totalBlocks":0,"skippedPages":0}
+                """;
+        InputStream stream = new ByteArrayInputStream(ndjson.getBytes(StandardCharsets.UTF_8));
+
+        List<OcrStreamEvent> events = new ArrayList<>();
+        RestClientOcrClient.parseNdjsonStream(stream, events::add);
+
+        assertThat(events).hasSize(4);
+        assertThat(events.get(1)).isInstanceOf(OcrStreamEvent.Preprocessing.class);
+        var preprocessing = (OcrStreamEvent.Preprocessing) events.get(1);
+        assertThat(preprocessing.pageNumber()).isEqualTo(1);
+    }
+
     @Test
     void parseNdjsonStream_ignoresUnknownEventTypes() {
         String ndjson = """