feat: inject per-chunk metadata (page, source) as XML into summarization input

Each chunk now includes its page number and source path as XML metadata
before the text content, giving the LLM context for citations.

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

Author: thiswillbeyourgithub

wdoc/utils/tasks/summarize.py

@@ -523,12 +523,28 @@ def _summarize(
     for ird, rd in tqdm(enumerate(docs), desc="Summarising splits", total=len(docs)):
         fixed_index = f"{ird + 1}/{len(docs)}"
 
+        # Build chunk text with per-chunk metadata if available
+        chunk_text = rd.page_content
+        chunk_meta_parts = []
+        if hasattr(rd, "metadata") and rd.metadata:
+            if "page" in rd.metadata:
+                chunk_meta_parts.append(f"<page>{rd.metadata['page']}</page>")
+            if "source" in rd.metadata:
+                chunk_meta_parts.append(f"<source>{rd.metadata['source']}</source>")
+        if chunk_meta_parts:
+            chunk_metadata_xml = (
+                "<chunk_metadata>\n"
+                + "\n".join(chunk_meta_parts)
+                + "\n</chunk_metadata>\n\n"
+            )
+            chunk_text = chunk_metadata_xml + chunk_text
+
         messages = BASE_SUMMARY_PROMPT.format_messages(
             language=language,
             metadata=metadata.replace("[PROGRESS]", fixed_index),
             previous_summary=previous_summary,
             recursion_instruction="" if not n_recursion else RECURSION_INSTRUCTION,
-            text=rd.page_content,
+            text=chunk_text,
         )
         if " object at " in llm._get_llm_string():
             logger.warning(