Deliver explainability triples inline in retrieval response stream (#763)

Provenance triples are now included directly in explain messages from
GraphRAG, DocumentRAG, and Agent services, eliminating the need for
follow-up knowledge graph queries to retrieve explainability details.

Each explain message in the response stream now carries:
- explain_id: root URI for this provenance step (unchanged)
- explain_graph: named graph where triples are stored (unchanged)
- explain_triples: the actual provenance triples for this step (new)

Changes across the stack:
- Schema: added explain_triples field to GraphRagResponse,
  DocumentRagResponse, and AgentResponse
- Services: all explain message call sites pass triples through
  (graph_rag, document_rag, agent react, agent orchestrator)
- Translators: encode explain_triples via TripleTranslator for
  gateway wire format
- Python SDK: ProvenanceEvent now includes parsed ExplainEntity
  and raw triples; expanded event_type detection
- CLI: invoke_graph_rag, invoke_agent, invoke_document_rag use
  inline entity when available, fall back to graph query
- Tech specs updated

Additional explainability test

trustgraph-base/trustgraph/api/socket_client.py

@@ -366,19 +366,13 @@ class SocketClient:
         # Handle GraphRAG/DocRAG message format with message_type
         if message_type == "explain":
             if include_provenance:
-                return ProvenanceEvent(
-                    explain_id=resp.get("explain_id", ""),
-                    explain_graph=resp.get("explain_graph", "")
-                )
+                return self._build_provenance_event(resp)
             return None
 
         # Handle Agent message format with chunk_type="explain"
         if chunk_type == "explain":
             if include_provenance:
-                return ProvenanceEvent(
-                    explain_id=resp.get("explain_id", ""),
-                    explain_graph=resp.get("explain_graph", "")
-                )
+                return self._build_provenance_event(resp)
             return None
 
         if chunk_type == "thought":
@@ -413,6 +407,42 @@ class SocketClient:
                 error=None
             )
 
+    def _build_provenance_event(self, resp: Dict[str, Any]) -> ProvenanceEvent:
+        """Build a ProvenanceEvent from a response dict, parsing inline triples
+        into an ExplainEntity if available."""
+        explain_id = resp.get("explain_id", "")
+        explain_graph = resp.get("explain_graph", "")
+        raw_triples = resp.get("explain_triples", [])
+
+        entity = None
+        if raw_triples:
+            try:
+                from .explainability import ExplainEntity
+                # Convert wire-format triple dicts to (s, p, o) tuples
+                parsed = []
+                for t in raw_triples:
+                    s = t.get("s", {}).get("i", "") if t.get("s") else ""
+                    p = t.get("p", {}).get("i", "") if t.get("p") else ""
+                    o_term = t.get("o", {})
+                    if o_term:
+                        if o_term.get("t") == "i":
+                            o = o_term.get("i", "")
+                        else:
+                            o = o_term.get("v", "")
+                    else:
+                        o = ""
+                    parsed.append((s, p, o))
+                entity = ExplainEntity.from_triples(explain_id, parsed)
+            except Exception:
+                pass
+
+        return ProvenanceEvent(
+            explain_id=explain_id,
+            explain_graph=explain_graph,
+            entity=entity,
+            triples=raw_triples,
+        )
+
     def close(self) -> None:
         """Close the persistent WebSocket connection."""
         if self._loop and not self._loop.is_closed():