feat: complete knowledge core storage — named graphs, provenance, source material (#973)

Implements all three changes from the knowledge-core-completeness tech spec:

1. Named graph field preserved through Cassandra storage (7-element tuple),
   enabling provenance triples to retain their graph URIs on round-trip.

2. Provenance triples already arrive on triples-input — no routing change
   needed; Change 1 was sufficient.

3. Source material (library documents) streamed alongside triples and
   embeddings during core download/upload. The knowledge manager fetches
   the document hierarchy from the librarian on download and recreates it
   on upload, preserving the full provenance chain across instances.

tests/unit/test_translators/test_knowledge_translator_roundtrip.py

@@ -1,5 +1,6 @@
 """
-Round-trip unit tests for KnowledgeRequestTranslator.
+Round-trip unit tests for KnowledgeRequestTranslator and
+KnowledgeResponseTranslator.
 
 Regression coverage: a previous version of the decode side constructed
 EntityEmbeddings(vectors=...) — the schema field is `vector` (singular),
@@ -15,9 +16,13 @@ Triples breaks the test.
 
 import pytest
 
-from trustgraph.messaging.translators.knowledge import KnowledgeRequestTranslator
+from trustgraph.messaging.translators.knowledge import (
+    KnowledgeRequestTranslator,
+    KnowledgeResponseTranslator,
+)
 from trustgraph.schema import (
     KnowledgeRequest,
+    KnowledgeResponse,
     GraphEmbeddings,
     EntityEmbeddings,
     Triples,
@@ -25,6 +30,8 @@ from trustgraph.schema import (
     Metadata,
     Term,
     IRI,
+    LibraryMetadata,
+    LibraryBlob,
 )
 
 
@@ -145,3 +152,161 @@ class TestKnowledgeRequestTranslatorTriples:
         assert t.s.iri == "http://example.org/alice"
         assert t.p.iri == "http://example.org/knows"
         assert t.o.iri == "http://example.org/bob"
+
+
+class TestKnowledgeRequestTranslatorLibrary:
+
+    def test_roundtrip_preserves_library_metadata(self, translator):
+        request = KnowledgeRequest(
+            operation="put-kg-core",
+            id="doc-1",
+            library_metadata=LibraryMetadata(
+                id="doc-1",
+                kind="application/pdf",
+                title="Test Document",
+                parent_id="",
+                document_type="source",
+                comments="test comments",
+                tags=["tag1", "tag2"],
+            ),
+        )
+
+        encoded = translator.encode(request)
+        assert "library-metadata" in encoded
+        lm = encoded["library-metadata"]
+        assert lm["id"] == "doc-1"
+        assert lm["kind"] == "application/pdf"
+        assert lm["title"] == "Test Document"
+        assert lm["parent-id"] == ""
+        assert lm["document-type"] == "source"
+        assert lm["comments"] == "test comments"
+        assert lm["tags"] == ["tag1", "tag2"]
+
+        decoded = translator.decode(encoded)
+        assert decoded.library_metadata is not None
+        assert decoded.library_metadata.id == "doc-1"
+        assert decoded.library_metadata.kind == "application/pdf"
+        assert decoded.library_metadata.title == "Test Document"
+        assert decoded.library_metadata.parent_id == ""
+        assert decoded.library_metadata.document_type == "source"
+        assert decoded.library_metadata.comments == "test comments"
+        assert decoded.library_metadata.tags == ["tag1", "tag2"]
+
+    def test_roundtrip_preserves_child_document_metadata(self, translator):
+        request = KnowledgeRequest(
+            operation="put-kg-core",
+            id="doc-1",
+            library_metadata=LibraryMetadata(
+                id="chunk-1",
+                kind="text/plain",
+                title="Chunk 1",
+                parent_id="doc-1",
+                document_type="chunk",
+            ),
+        )
+
+        encoded = translator.encode(request)
+        decoded = translator.decode(encoded)
+
+        assert decoded.library_metadata.parent_id == "doc-1"
+        assert decoded.library_metadata.document_type == "chunk"
+
+    def test_roundtrip_preserves_library_blob(self, translator):
+        request = KnowledgeRequest(
+            operation="put-kg-core",
+            id="doc-1",
+            library_blob=LibraryBlob(
+                id="doc-1",
+                data=b"SGVsbG8gV29ybGQ=",
+            ),
+        )
+
+        encoded = translator.encode(request)
+        assert "library-blob" in encoded
+        assert encoded["library-blob"]["id"] == "doc-1"
+        assert encoded["library-blob"]["data"] == "SGVsbG8gV29ybGQ="
+
+        decoded = translator.decode(encoded)
+        assert decoded.library_blob is not None
+        assert decoded.library_blob.id == "doc-1"
+        assert decoded.library_blob.data == "SGVsbG8gV29ybGQ="
+
+    def test_absent_library_fields_decode_as_none(self, translator):
+        decoded = translator.decode({
+            "operation": "get-kg-core",
+            "id": "doc-1",
+        })
+        assert decoded.library_metadata is None
+        assert decoded.library_blob is None
+
+
+class TestKnowledgeResponseTranslatorLibrary:
+
+    @pytest.fixture
+    def response_translator(self):
+        return KnowledgeResponseTranslator()
+
+    def test_encode_library_metadata(self, response_translator):
+        response = KnowledgeResponse(
+            ids=None,
+            library_metadata=LibraryMetadata(
+                id="doc-1",
+                kind="application/pdf",
+                title="Test",
+                parent_id="",
+                document_type="source",
+                comments="",
+                tags=[],
+            ),
+        )
+        encoded = response_translator.encode(response)
+        assert "library-metadata" in encoded
+        assert encoded["library-metadata"]["id"] == "doc-1"
+        assert encoded["library-metadata"]["kind"] == "application/pdf"
+        assert encoded["library-metadata"]["document-type"] == "source"
+
+    def test_encode_library_blob_bytes_to_string(self, response_translator):
+        response = KnowledgeResponse(
+            ids=None,
+            library_blob=LibraryBlob(
+                id="doc-1",
+                data=b"dGVzdCBkYXRh",
+            ),
+        )
+        encoded = response_translator.encode(response)
+        assert "library-blob" in encoded
+        assert encoded["library-blob"]["id"] == "doc-1"
+        assert encoded["library-blob"]["data"] == "dGVzdCBkYXRh"
+        assert isinstance(encoded["library-blob"]["data"], str)
+
+    def test_encode_library_blob_string_passthrough(self, response_translator):
+        response = KnowledgeResponse(
+            ids=None,
+            library_blob=LibraryBlob(
+                id="doc-1",
+                data="already-a-string",
+            ),
+        )
+        encoded = response_translator.encode(response)
+        assert encoded["library-blob"]["data"] == "already-a-string"
+
+    def test_library_metadata_is_not_final(self, response_translator):
+        response = KnowledgeResponse(
+            ids=None,
+            library_metadata=LibraryMetadata(id="doc-1"),
+        )
+        _, is_final = response_translator.encode_with_completion(response)
+        assert is_final is False
+
+    def test_library_blob_is_not_final(self, response_translator):
+        response = KnowledgeResponse(
+            ids=None,
+            library_blob=LibraryBlob(id="doc-1", data=b"data"),
+        )
+        _, is_final = response_translator.encode_with_completion(response)
+        assert is_final is False
+
+    def test_eos_is_final(self, response_translator):
+        response = KnowledgeResponse(eos=True)
+        _, is_final = response_translator.encode_with_completion(response)
+        assert is_final is True