diff --git a/app/ingestion/pipeline.py b/app/ingestion/pipeline.py
index 9ce433b..e7717af 100644
--- a/app/ingestion/pipeline.py
+++ b/app/ingestion/pipeline.py
@@ -20,7 +20,6 @@ from app.db.models import (
     ArtifactType,
     Chunk,
     Document,
-    DocumentArtifact,
     DocumentStatus,
     Page,
     ProcessingEvent,
@@ -35,7 +34,7 @@ from app.ingestion.knowledge_ingest import load_asset_metadata_for_document
 from app.ingestion.ocr import run_ocr
 from app.ingestion.table_processor import persist_tables
 from app.logging_config import get_logger
-from app.storage.artifacts import ensure_artifact
+from app.storage.artifacts import ensure_artifact, latest_artifact
 from app.storage.local_paths import (
     key_docling_json,
     key_markdown,
@@ -65,12 +64,9 @@ def process_document_id(  # noqa: PLR0911, PLR0912, PLR0915
 
         source_path = Path(doc.source_path)
         sha = doc.sha256
-        original_artifact = db.execute(
-            select(DocumentArtifact).where(
-                DocumentArtifact.document_id == doc.id,
-                DocumentArtifact.artifact_type == ArtifactType.ORIGINAL_PDF,
-            )
-        ).scalar_one_or_none()
+        original_artifact = latest_artifact(
+            db, document_id=doc.id, artifact_type=ArtifactType.ORIGINAL_PDF
+        )
 
     work_dir = work_dir_for(document_id)
     local_pdf = work_dir / f"{sha}.pdf"
diff --git a/app/storage/artifacts.py b/app/storage/artifacts.py
index 13d11f4..3578705 100644
--- a/app/storage/artifacts.py
+++ b/app/storage/artifacts.py
@@ -51,3 +51,32 @@ def ensure_artifact(
     )
     db.add(artifact)
     return artifact
+
+
+def latest_artifact(
+    db: Session,
+    *,
+    document_id: uuid.UUID,
+    artifact_type: str,
+) -> DocumentArtifact | None:
+    """Newest artifact of the given type, or ``None``.
+
+    Duplicates of one type are legal: repeated knowledge-ingest of identical
+    content (same sha256, new asset_id → new canonical object key) appends a
+    second ORIGINAL_PDF row because ensure_artifact identity is
+    (document_id, storage_key). All such rows reference byte-identical objects
+    (sha256 verified at ingest), so the newest reference is always a safe,
+    deterministic pick — never scalar_one_or_none here (G6 MultipleResultsFound).
+    """
+    return (
+        db.execute(
+            select(DocumentArtifact)
+            .where(
+                DocumentArtifact.document_id == document_id,
+                DocumentArtifact.artifact_type == artifact_type,
+            )
+            .order_by(DocumentArtifact.created_at.desc(), DocumentArtifact.id.desc())
+        )
+        .scalars()
+        .first()
+    )
diff --git a/tests/test_artifact_lookup.py b/tests/test_artifact_lookup.py
new file mode 100644
index 0000000..aee9e27
--- /dev/null
+++ b/tests/test_artifact_lookup.py
@@ -0,0 +1,93 @@
+"""G6: ORIGINAL_PDF artifact lookup must tolerate duplicate rows.
+
+Repeated knowledge-ingest of identical content (same sha256, new asset_id →
+new canonical object key) reuses the Document row but appends a second
+ORIGINAL_PDF artifact (ensure_artifact identity is document_id+storage_key).
+The old ``scalar_one_or_none()`` in ``process_document_id`` then raised
+``MultipleResultsFound`` → Celery retry storm. The lookup must instead pick
+the newest artifact deterministically — any row is byte-identical (sha256
+verified at ingest), so the latest reference is always safe.
+"""
+
+from __future__ import annotations
+
+import uuid
+
+from app.db.models import ArtifactType, DocumentArtifact
+from app.storage.artifacts import latest_artifact
+
+
+class _FakeScalars:
+    def __init__(self, rows):
+        self._rows = rows
+
+    def first(self):
+        return self._rows[0] if self._rows else None
+
+
+class _FakeResult:
+    def __init__(self, rows):
+        self._rows = rows
+
+    def scalars(self):
+        return _FakeScalars(self._rows)
+
+
+class _FakeSession:
+    def __init__(self, rows):
+        self.rows = rows
+        self.statements = []
+
+    def execute(self, stmt):
+        self.statements.append(stmt)
+        return _FakeResult(self.rows)
+
+
+def _artifact(key: str) -> DocumentArtifact:
+    return DocumentArtifact(
+        id=uuid.uuid4(),
+        document_id=uuid.uuid4(),
+        artifact_type=ArtifactType.ORIGINAL_PDF,
+        storage_bucket="teamhub-mailhub-originals",
+        storage_key=key,
+    )
+
+
+def test_latest_artifact_returns_first_row_without_raising():
+    rows = [_artifact("mailhub/2026/07/11/b/original/x.pdf"),
+            _artifact("mailhub/2026/07/11/a/original/x.pdf")]
+    db = _FakeSession(rows)
+    got = latest_artifact(db, document_id=rows[0].document_id,
+                          artifact_type=ArtifactType.ORIGINAL_PDF)
+    assert got is rows[0]
+
+
+def test_latest_artifact_none_when_absent():
+    db = _FakeSession([])
+    assert latest_artifact(db, document_id=uuid.uuid4(),
+                           artifact_type=ArtifactType.ORIGINAL_PDF) is None
+
+
+def test_latest_artifact_query_is_deterministic_newest_first():
+    """The emitted SQL must filter by document_id+artifact_type and order
+    newest-first with a stable tiebreaker — that is what makes the pick
+    deterministic when duplicates exist."""
+    db = _FakeSession([])
+    latest_artifact(db, document_id=uuid.uuid4(), artifact_type=ArtifactType.ORIGINAL_PDF)
+    (stmt,) = db.statements
+    sql = str(stmt.compile(compile_kwargs={"literal_binds": False}))
+    assert "document_artifacts.document_id" in sql
+    assert "document_artifacts.artifact_type" in sql
+    assert "ORDER BY document_artifacts.created_at DESC, document_artifacts.id DESC" in sql
+
+
+def test_pipeline_uses_tolerant_lookup():
+    """process_document_id must not use scalar_one_or_none for the ORIGINAL_PDF
+    lookup (the G6 crash); it goes through latest_artifact instead."""
+    import inspect
+
+    from app.ingestion import pipeline
+
+    src = inspect.getsource(pipeline.process_document_id)
+    assert "latest_artifact" in src
+    assert "scalar_one_or_none" not in src