feat(storage): X14 Phase 2b — route extracted-text + async DOCX exports through storage.py

Continue the write-site rewiring onto the unified storage layer (INV-STG1):
- services/processor.py: extracted-text .txt → DERIVED bucket (a derived
  artifact; the DB column is the source of truth per INV-STG5, so the write
  stays non-fatal)
- services/docx_exporter.py (export_decision): DOCX → DOCUMENTS bucket via
  BytesIO → put_bytes, with a fallback to a direct disk write when the caller
  passes an output_path outside DATA_DIR
- services/analysis_docx_exporter.py (build_analysis_docx): same pattern;
  out_path is always under DATA_DIR

Under the default STORAGE_BACKEND=filesystem the bytes land at the exact
legacy path (put_bytes → DATA_DIR/key), so behaviour is unchanged. The
disk-reading bits that must stay for now (export_dir glob in _next_version)
are kept; storage-native versioning is a cutover concern.

Still on disk (sync call-sites, follow-up Phase 2c): docx_reviser
(track-changes), docx_retrofit backup, and multimodal thumbnails (rendered in
a to_thread). git-tracked text (case.json/notes/research-md/draft-md) stays on
disk by design (INV-STG7).

tests: 38 storage + docx tests green (incl. test_export_qa_gate /
test_docx_exporter_bookmarks which exercise the real export path); 242
collected, no import breakage.

Keeps G2; advances INV-STG1. Spec: docs/spec/X14-storage-minio.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

mcp-server/src/legal_mcp/services/processor.py

@@ -8,7 +8,9 @@ from pathlib import Path
 from uuid import UUID
 
 from legal_mcp import config
-from legal_mcp.services import chunker, db, embeddings, extractor, references_extractor
+from legal_mcp.services import (
+    chunker, db, embeddings, extractor, references_extractor, storage,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -40,13 +42,17 @@ async def process_document(document_id: UUID, case_id: UUID) -> dict:
             page_count=page_count,
         )
 
-        # Save extracted text to documents/extracted/ directory
+        # Save extracted text (a DERIVED artifact — the DB column holds the
+        # source of truth, INV-STG5) through the storage layer (INV-STG1).
+        # Non-fatal: the .txt is a convenience copy, the pipeline reads the DB.
         original_path = Path(doc["file_path"])
-        extracted_dir = original_path.parent.parent / "extracted"
-        extracted_dir.mkdir(parents=True, exist_ok=True)
-        txt_path = extracted_dir / (original_path.stem + ".txt")
+        txt_path = original_path.parent.parent / "extracted" / (original_path.stem + ".txt")
         try:
-            txt_path.write_text(text, encoding="utf-8")
+            await storage.put_bytes(
+                txt_path.relative_to(config.DATA_DIR).as_posix(),
+                text.encode("utf-8"), bucket=storage.Bucket.DERIVED,
+                content_type="text/plain; charset=utf-8",
+            )
             logger.info("Saved extracted text to %s", txt_path)
         except Exception as e:
             logger.warning("Failed to save text file (non-fatal): %s", e)