Adding explainability to the ReACT agent (#689)

* Added tech spec

* Add provenance recording to React agent loop

Enables agent sessions to be traced and debugged using the same
explainability infrastructure as GraphRAG. Agent traces record:
- Session start with query and timestamp
- Each iteration's thought, action, arguments, and observation
- Final answer with derivation chain

Changes:
- Add session_id and collection fields to AgentRequest schema
- Add agent predicates (TG_THOUGHT, TG_ACTION, etc.) to namespaces
- Create agent provenance triple generators in provenance/agent.py
- Register explainability producer in agent service
- Emit provenance triples during agent execution
- Update CLI tools to detect and render agent traces alongside GraphRAG

* Updated explainability taxonomy:

GraphRAG: tg:Question → tg:Exploration → tg:Focus → tg:Synthesis

Agent: tg:Question → tg:Analysis(s) → tg:Conclusion

All entities also have their PROV-O type (prov:Activity or prov:Entity).

Updated commit message:

Add provenance recording to React agent loop

Enables agent sessions to be traced and debugged using the same
explainability infrastructure as GraphRAG.

Entity types follow human reasoning patterns:
- tg:Question - the user's query (shared with GraphRAG)
- tg:Analysis - each think/act/observe cycle
- tg:Conclusion - the final answer

Also adds explicit TG types to GraphRAG entities:
- tg:Question, tg:Exploration, tg:Focus, tg:Synthesis

All types retain their PROV-O base types (prov:Activity, prov:Entity).

Changes:
- Add session_id and collection fields to AgentRequest schema
- Add explainability entity types to namespaces.py
- Create agent provenance triple generators
- Register explainability producer in agent service
- Emit provenance triples during agent execution
- Update CLI tools to detect and render both trace types

* Document RAG explainability is now complete. Here's a summary of the
changes made:

Schema Changes:
- trustgraph-base/trustgraph/schema/services/retrieval.py: Added
  explain_id and explain_graph fields to DocumentRagResponse
- trustgraph-base/trustgraph/messaging/translators/retrieval.py:
  Updated translator to handle explainability fields

Provenance Changes:
- trustgraph-base/trustgraph/provenance/namespaces.py: Added
  TG_CHUNK_COUNT and TG_SELECTED_CHUNK predicates
- trustgraph-base/trustgraph/provenance/uris.py: Added
  docrag_question_uri, docrag_exploration_uri, docrag_synthesis_uri
  generators
- trustgraph-base/trustgraph/provenance/triples.py: Added
  docrag_question_triples, docrag_exploration_triples,
  docrag_synthesis_triples builders
- trustgraph-base/trustgraph/provenance/__init__.py: Exported all
  new Document RAG functions and predicates

Service Changes:
- trustgraph-flow/trustgraph/retrieval/document_rag/document_rag.py:
  Added explainability callback support and triple emission at each
  phase (Question → Exploration → Synthesis)
- trustgraph-flow/trustgraph/retrieval/document_rag/rag.py:
  Registered explainability producer and wired up the callback

Documentation:
- docs/tech-specs/agent-explainability.md: Added Document RAG entity
  types and provenance model documentation

Document RAG Provenance Model:
Question (urn:trustgraph:docrag:{uuid})
    │
    │  tg:query, prov:startedAtTime
    │  rdf:type = prov:Activity, tg:Question
    │
    ↓ prov:wasGeneratedBy
    │
Exploration (urn:trustgraph:docrag:{uuid}/exploration)
    │
    │  tg:chunkCount, tg:selectedChunk (multiple)
    │  rdf:type = prov:Entity, tg:Exploration
    │
    ↓ prov:wasDerivedFrom
    │
Synthesis (urn:trustgraph:docrag:{uuid}/synthesis)
    │
    │  tg:content = "The answer..."
    │  rdf:type = prov:Entity, tg:Synthesis

* Specific subtype that makes the retrieval mechanism immediately
obvious:

System: GraphRAG
TG Types on Question: tg:Question, tg:GraphRagQuestion
URI Pattern: urn:trustgraph:question:{uuid}
────────────────────────────────────────
System: Document RAG
TG Types on Question: tg:Question, tg:DocRagQuestion
URI Pattern: urn:trustgraph:docrag:{uuid}
────────────────────────────────────────
System: Agent
TG Types on Question: tg:Question, tg:AgentQuestion
URI Pattern: urn:trustgraph:agent:{uuid}
Files modified:
- trustgraph-base/trustgraph/provenance/namespaces.py - Added
TG_GRAPH_RAG_QUESTION, TG_DOC_RAG_QUESTION, TG_AGENT_QUESTION
- trustgraph-base/trustgraph/provenance/triples.py - Added subtype to
question_triples and docrag_question_triples
- trustgraph-base/trustgraph/provenance/agent.py - Added subtype to
agent_session_triples
- trustgraph-base/trustgraph/provenance/__init__.py - Exported new types
- docs/tech-specs/agent-explainability.md - Documented the subtypes

This allows:
- Query all questions: ?q rdf:type tg:Question
- Query only GraphRAG: ?q rdf:type tg:GraphRagQuestion
- Query only Document RAG: ?q rdf:type tg:DocRagQuestion
- Query only Agent: ?q rdf:type tg:AgentQuestion

* Fixed tests

tests/unit/test_retrieval/test_document_rag.py

@@ -208,9 +208,12 @@ class TestQuery:
             collection="test_collection"
         )
 
-        # Verify result is list of fetched document content
-        assert "Document 1 content" in result
-        assert "Document 2 content" in result
+        # Verify result is tuple of (docs, chunk_ids)
+        docs, chunk_ids = result
+        assert "Document 1 content" in docs
+        assert "Document 2 content" in docs
+        assert "doc/c1" in chunk_ids
+        assert "doc/c2" in chunk_ids
 
     @pytest.mark.asyncio
     async def test_document_rag_query_method(self, mock_fetch_chunk):
@@ -350,8 +353,10 @@ class TestQuery:
         mock_embeddings_client.embed.assert_called_once_with(["verbose test"])
         mock_doc_embeddings_client.query.assert_called_once()
 
-        # Verify result contains fetched content
-        assert "Verbose test doc" in result
+        # Verify result is tuple of (docs, chunk_ids) with fetched content
+        docs, chunk_ids = result
+        assert "Verbose test doc" in docs
+        assert "doc/c6" in chunk_ids
 
     @pytest.mark.asyncio
     async def test_document_rag_query_with_verbose(self, mock_fetch_chunk):
@@ -426,8 +431,8 @@ class TestQuery:
         mock_embeddings_client.embed.assert_called_once_with(["query with no results"])
         mock_doc_embeddings_client.query.assert_called_once()
 
-        # Verify empty result is returned
-        assert result == []
+        # Verify empty result is returned (tuple of empty lists)
+        assert result == ([], [])
 
     @pytest.mark.asyncio
     async def test_document_rag_query_with_empty_documents(self, mock_fetch_chunk):