feat: persist and refresh chunk char spans on index

surfsense_backend/app/indexing_pipeline/indexing_pipeline_service.py

@@ -20,9 +20,10 @@ from app.db import (
     DocumentType,
 )
 from app.indexing_pipeline.cache import build_chunk_embeddings
-from app.indexing_pipeline.cache.cached_indexing import chunk_markdown, embed_batch
-from app.indexing_pipeline.chunk_reconciler import ExistingChunk, reconcile
+from app.indexing_pipeline.cache.cached_indexing import chunk_slices, embed_batch
+from app.indexing_pipeline.chunk_reconciler import ChunkPlan, ExistingChunk, reconcile
 from app.indexing_pipeline.connector_document import ConnectorDocument
+from app.indexing_pipeline.document_chunker import ChunkSlice
 from app.indexing_pipeline.document_hashing import (
     compute_content_hash,
     compute_identifier_hash,
@@ -489,12 +490,22 @@ class IndexingPipelineService:
 
     async def _load_existing_chunks(self, document_id: int) -> list[ExistingChunk]:
         result = await self.session.execute(
-            select(Chunk.id, Chunk.content, Chunk.position).where(
-                Chunk.document_id == document_id
-            )
+            select(
+                Chunk.id,
+                Chunk.content,
+                Chunk.position,
+                Chunk.start_char,
+                Chunk.end_char,
+            ).where(Chunk.document_id == document_id)
         )
         return [
-            ExistingChunk(id=row.id, content=row.content, position=row.position)
+            ExistingChunk(
+                id=row.id,
+                content=row.content,
+                position=row.position,
+                start_char=row.start_char,
+                end_char=row.end_char,
+            )
             for row in result
         ]
 
@@ -505,15 +516,21 @@ class IndexingPipelineService:
             delete(Chunk).where(Chunk.document_id == document.id)
         )
 
-        summary_embedding, chunk_pairs = await build_chunk_embeddings(
+        summary_embedding, slice_pairs = await build_chunk_embeddings(
             content,
             use_code_chunker=connector_doc.should_use_code_chunker,
         )
 
         document.embedding = summary_embedding
         return [
-            Chunk(content=text, embedding=emb, position=i)
-            for i, (text, emb) in enumerate(chunk_pairs)
+            Chunk(
+                content=chunk_slice.text,
+                embedding=emb,
+                position=i,
+                start_char=chunk_slice.start_char,
+                end_char=chunk_slice.end_char,
+            )
+            for i, (chunk_slice, emb) in enumerate(slice_pairs)
         ]
 
     async def _reindex_incrementally(
@@ -525,35 +542,39 @@ class IndexingPipelineService:
     ) -> int:
         """Edit path: keep rows whose text survived, embed only new texts.
 
-        Unchanged rows keep their embedding and their HNSW/GIN index entries;
-        moved rows get a position-only UPDATE, which touches neither index.
+        Unchanged rows keep their embedding and their HNSW/GIN index entries. An
+        edit can shift a kept chunk's char span without changing its text, so
+        every kept row's position and span are refreshed whenever they drift.
         """
-        new_texts = await chunk_markdown(
+        slices = await chunk_slices(
             content, use_code_chunker=connector_doc.should_use_code_chunker
         )
+        new_texts = [s.text for s in slices]
         plan = reconcile(existing, new_texts)
 
         # One batch: the document-level summary vector plus the missing chunks.
         embeddings = await embed_batch([content, *[t for _, t in plan.to_embed]])
         summary_embedding, *new_embeddings = embeddings
 
-        if plan.reused:
-            await self.session.execute(
-                update(Chunk),
-                [{"id": cid, "position": pos} for cid, pos in plan.reused],
-            )
         if plan.to_delete:
             await self.session.execute(
                 delete(Chunk).where(Chunk.id.in_(plan.to_delete))
             )
+
+        span_updates = self._kept_row_span_updates(existing, slices, plan)
+        if span_updates:
+            await self.session.execute(update(Chunk), span_updates)
+
         self.session.add_all(
             Chunk(
-                content=text,
+                content=slices[pos].text,
                 embedding=emb,
                 position=pos,
+                start_char=slices[pos].start_char,
+                end_char=slices[pos].end_char,
                 document_id=document.id,
             )
-            for (pos, text), emb in zip(plan.to_embed, new_embeddings, strict=True)
+            for (pos, _text), emb in zip(plan.to_embed, new_embeddings, strict=True)
         )
         document.embedding = summary_embedding
 
@@ -564,6 +585,36 @@ class IndexingPipelineService:
         )
         return len(new_texts)
 
+    @staticmethod
+    def _kept_row_span_updates(
+        existing: list[ExistingChunk],
+        slices: list[ChunkSlice],
+        plan: ChunkPlan,
+    ) -> list[dict]:
+        """Position/span writes for kept rows, emitted only where a value drifts."""
+        deleted = set(plan.to_delete)
+        moved = dict(plan.reused)
+        updates: list[dict] = []
+        for chunk in existing:
+            if chunk.id in deleted:
+                continue
+            new_position = moved.get(chunk.id, chunk.position)
+            target = slices[new_position]
+            if (
+                chunk.position != new_position
+                or chunk.start_char != target.start_char
+                or chunk.end_char != target.end_char
+            ):
+                updates.append(
+                    {
+                        "id": chunk.id,
+                        "position": new_position,
+                        "start_char": target.start_char,
+                        "end_char": target.end_char,
+                    }
+                )
+        return updates
+
     async def _enqueue_ai_sort_if_enabled(self, document: Document) -> None:
         """Fire-and-forget: enqueue incremental AI sort if the search space has it enabled."""
         try: