Reuse one MarkdownDocSerializer per document in item extraction

CHANGELOG.md

@@ -5,6 +5,7 @@
 
 - zstd compression uses a fresh `zstandard` compressor/decompressor per call instead of shared module-level singletons, fixing process segfaults when ingester workers compress documents concurrently (Python < 3.14).
 - Ingestion compresses the DoclingDocument structure directly from the in-memory dict, removing one full-size serialized copy from per-document peak memory.
+- Document item extraction builds one `MarkdownDocSerializer` per document (reused across tables) and derives description-less picture text from captions, instead of constructing a serializer per picture and table.
 
 ## [0.61.0] - 2026-06-23
 

haiku_rag_slim/haiku/rag/store/models/document_item.py

@@ -1,5 +1,6 @@
 import base64
-from typing import TYPE_CHECKING
+from collections.abc import Callable
+from typing import TYPE_CHECKING, Any
 
 from pydantic import BaseModel
 
@@ -53,18 +54,33 @@ def _decode_picture_bytes(item: "PictureItem") -> bytes | None:
     return base64.b64decode(encoded, validate=False)
 
 
-def extract_item_text(item: "NodeItem", docling_doc: "DoclingDocument") -> str | None:
+def _picture_caption_text(item: "PictureItem", docling_doc: "DoclingDocument") -> str:
+    """Join a picture's caption texts with spaces, preserving word boundaries."""
+    return " ".join(
+        text
+        for caption in item.captions
+        if (text := caption.resolve(docling_doc).text.strip())
+    )
+
+
+def extract_item_text(
+    item: "NodeItem",
+    docling_doc: "DoclingDocument",
+    *,
+    get_serializer: Callable[[], Any] | None = None,
+) -> str | None:
     """Extract text content from a DocItem.
 
     Handles different item types:
     - TextItem, SectionHeaderItem, etc.: Use .text attribute
-    - TableItem: Use export_to_markdown() for table content
+    - TableItem: serialize to markdown. ``get_serializer`` supplies a reused
+      ``MarkdownDocSerializer`` (see ``extract_items``); when absent a one-off
+      serializer is built so direct calls keep working.
     - PictureItem: Prefer the VLM description (when picture_description is on)
       so pictures carry meaningful prose into chunk text and survive
       ``expand_with_items``' ``if item.text:`` filter; otherwise fall back to
-      a placeholder markdown export (no base64).
+      the picture's caption text.
     """
-    from docling_core.types.doc.base import ImageRefMode
     from docling_core.types.doc.document import PictureItem, TableItem
 
     if text := getattr(item, "text", None):
@@ -73,15 +89,19 @@ def extract_item_text(item: "NodeItem", docling_doc: "DoclingDocument") -> str |
     if isinstance(item, PictureItem):
         if description := _picture_description_text(item):
             return description
-        return item.export_to_markdown(
+        return _picture_caption_text(item, docling_doc)
-            docling_doc,
-            image_mode=ImageRefMode.PLACEHOLDER,
-            image_placeholder="",
-        )
 
     if isinstance(item, TableItem):
         try:
-            return item.export_to_markdown(docling_doc)
+            if get_serializer is None:
+                from docling_core.transforms.serializer.markdown import (
+                    MarkdownDocSerializer,
+                )
+
+                serializer = MarkdownDocSerializer(doc=docling_doc)
+            else:
+                serializer = get_serializer()
+            return serializer.serialize(item=item).text
         except Exception:
             pass
 
@@ -116,11 +136,23 @@ def extract_items(
     existing = existing_picture_data or {}
     items: list[DocumentItem] = []
 
+    serializer: Any = None
+
+    def get_serializer() -> Any:
+        nonlocal serializer
+        if serializer is None:
+            from docling_core.transforms.serializer.markdown import (
+                MarkdownDocSerializer,
+            )
+
+            serializer = MarkdownDocSerializer(doc=docling_doc)
+        return serializer
+
     for position, (item, level) in enumerate(docling_doc.iterate_items()):
         label = getattr(item, "label", None)
         label_str = str(label.value) if hasattr(label, "value") else str(label or "")
 
-        text = extract_item_text(item, docling_doc) or ""
+        text = extract_item_text(item, docling_doc, get_serializer=get_serializer) or ""
 
         page_numbers: list[int] = []
         if prov := getattr(item, "prov", None):

tests/store/test_document_items.py

@@ -140,6 +140,112 @@ class TestExtractItemText:
         assert items == []
 
 
+def _doc_with_captioned_picture(*captions: str):
+    from docling_core.types.doc.document import DoclingDocument, ImageRef
+    from docling_core.types.doc.labels import DocItemLabel
+    from PIL import Image
+
+    doc = DoclingDocument(name="pics")
+    caption_items = [doc.add_text(label=DocItemLabel.CAPTION, text=c) for c in captions]
+    img = ImageRef.from_pil(Image.new("RGB", (8, 8), "red"), dpi=72)
+    doc.add_picture(image=img, caption=caption_items[0] if caption_items else None)
+    pic = doc.pictures[0]
+    for extra in caption_items[1:]:
+        pic.captions.append(extra.get_ref())
+    return doc, pic
+
+
+def _doc_with_tables(n: int):
+    from docling_core.types.doc.document import DoclingDocument, TableCell, TableData
+
+    doc = DoclingDocument(name="tables")
+    for _ in range(n):
+        cells = [
+            TableCell(
+                text=f"r{r}c{c}",
+                row_span=1,
+                col_span=1,
+                start_row_offset_idx=r,
+                end_row_offset_idx=r + 1,
+                start_col_offset_idx=c,
+                end_col_offset_idx=c + 1,
+            )
+            for r in range(2)
+            for c in range(2)
+        ]
+        doc.add_table(data=TableData(num_rows=2, num_cols=2, table_cells=cells))
+    return doc
+
+
+class TestExtractItemTextPictures:
+    """Description-less pictures derive text from captions, without a serializer."""
+
+    def test_multiple_captions_space_joined(self):
+        doc, pic = _doc_with_captioned_picture("First", "Second")
+        assert extract_item_text(pic, doc) == "First Second"
+
+    def test_description_wins_over_captions(self):
+        from docling_core.types.doc.document import DescriptionMetaField, PictureMeta
+
+        doc, pic = _doc_with_captioned_picture("A caption")
+        pic.meta = PictureMeta(description=DescriptionMetaField(text="A red square."))
+        assert extract_item_text(pic, doc) == "A red square."
+
+    def test_picture_path_does_not_export_markdown(self, monkeypatch):
+        from docling_core.types.doc.document import PictureItem
+
+        doc, pic = _doc_with_captioned_picture("Only caption")
+
+        def _boom(*args, **kwargs):
+            raise AssertionError("picture path must not build a serializer")
+
+        monkeypatch.setattr(PictureItem, "export_to_markdown", _boom)
+        assert extract_item_text(pic, doc) == "Only caption"
+
+    def test_picture_path_never_requests_serializer(self):
+        doc, pic = _doc_with_captioned_picture("Only caption")
+
+        def _explode():
+            raise AssertionError("picture path must not request a serializer")
+
+        assert extract_item_text(pic, doc, get_serializer=_explode) == "Only caption"
+
+
+class TestExtractItemsTableSerializer:
+    """Table text is unchanged; one serializer is reused across the whole pass."""
+
+    def test_table_text_matches_export_to_markdown(self):
+        doc = _doc_with_tables(1)
+        expected = doc.tables[0].export_to_markdown(doc)
+        items = extract_items("doc-1", doc)
+        table_items = [i for i in items if i.label == "table"]
+        assert len(table_items) == 1
+        assert table_items[0].text == expected
+
+    def test_one_serializer_built_for_multiple_tables(self, monkeypatch):
+        import docling_core.transforms.serializer.markdown as md
+
+        count = {"n": 0}
+        base = md.MarkdownDocSerializer
+
+        class Counting(base):
+            def __init__(self, *args, **kwargs):
+                count["n"] += 1
+                super().__init__(*args, **kwargs)
+
+        doc = _doc_with_tables(3)
+        monkeypatch.setattr(md, "MarkdownDocSerializer", Counting)
+
+        items = extract_items("doc-1", doc)
+        assert sum(1 for i in items if i.label == "table") == 3
+        assert count["n"] == 1
+
+    def test_direct_table_call_builds_one_off_serializer(self):
+        doc = _doc_with_tables(1)
+        expected = doc.tables[0].export_to_markdown(doc)
+        assert extract_item_text(doc.tables[0], doc) == expected
+
+
 @pytest.mark.asyncio
 class TestDocumentItemRepository:
     async def test_create_and_get_range(self, temp_db_path):