feat: direction-aware reranker text in GraphRAG hop-and-filter (#1016)

The reranker document text now reflects the traversal direction,
showing only the new information relative to the frontier entity:
- From S (subject is frontier): text = "{predicate} {object}"
- From O (object is frontier): text = "{subject} {predicate}"
- From P (predicate is frontier): text = "{subject} {object}"

This eliminates duplicate reranker texts when traversing inward
from shared object nodes (e.g. 18 CPUs all producing identical
"hasSubcategory Processors" text when the subject was dropped).

execute_batch_triple_queries now returns (triple, direction)
tuples so hop_and_filter can select the appropriate text format.

Updates tech spec to document the direction-aware approach.
Adds unit tests for direction tracking and reranker text
construction.

tests/unit/test_concurrency/test_graph_rag_concurrency.py

@@ -129,6 +129,9 @@ class TestBatchTripleQueries:
 
         # 3 queries, alternating results
         assert len(result) == 3
+        # Each result is a (triple, direction) tuple
+        for triple, direction in result:
+            assert direction in (Query.FROM_S, Query.FROM_P, Query.FROM_O)
 
     @pytest.mark.asyncio
     async def test_exception_in_one_query_does_not_block_others(self):
@@ -153,6 +156,8 @@ class TestBatchTripleQueries:
 
         # 3 queries: 2 succeed, 1 fails → 2 triples
         assert len(result) == 2
+        for triple, direction in result:
+            assert direction in (Query.FROM_S, Query.FROM_P, Query.FROM_O)
 
     @pytest.mark.asyncio
     async def test_none_results_filtered(self):
@@ -176,6 +181,8 @@ class TestBatchTripleQueries:
 
         # 3 queries: 1 returns None, 2 return triples
         assert len(result) == 2
+        for triple, direction in result:
+            assert direction in (Query.FROM_S, Query.FROM_P, Query.FROM_O)
 
     @pytest.mark.asyncio
     async def test_empty_entities_no_queries(self):
@@ -220,6 +227,80 @@ class TestBatchTripleQueries:
         assert calls[2].kwargs["p"] is None
         assert calls[2].kwargs["o"] == "ent-1"
 
+    @pytest.mark.asyncio
+    async def test_directions_assigned_correctly(self):
+        """Each query position should produce the correct direction tag."""
+        triple = _make_triple("s", "p", "o")
+
+        call_count = 0
+
+        async def one_triple_each(**kwargs):
+            nonlocal call_count
+            call_count += 1
+            return [triple]
+
+        client = AsyncMock()
+        client.query_stream = one_triple_each
+        query = _make_query(triples_client=client)
+
+        result = await query.execute_batch_triple_queries(
+            ["e1"], limit_per_entity=10
+        )
+
+        assert len(result) == 3
+        # Order matches query order: s-position, p-position, o-position
+        assert result[0][1] == Query.FROM_S
+        assert result[1][1] == Query.FROM_P
+        assert result[2][1] == Query.FROM_O
+
+    @pytest.mark.asyncio
+    async def test_directions_correct_for_multiple_entities(self):
+        """Direction tags cycle correctly across multiple entities."""
+        triple = _make_triple("s", "p", "o")
+        client = AsyncMock()
+        client.query_stream = AsyncMock(return_value=[triple])
+        query = _make_query(triples_client=client)
+
+        result = await query.execute_batch_triple_queries(
+            ["e1", "e2"], limit_per_entity=10
+        )
+
+        assert len(result) == 6
+        expected_directions = [
+            Query.FROM_S, Query.FROM_P, Query.FROM_O,
+            Query.FROM_S, Query.FROM_P, Query.FROM_O,
+        ]
+        for (_, direction), expected in zip(result, expected_directions):
+            assert direction == expected
+
+    @pytest.mark.asyncio
+    async def test_direction_preserved_with_multiple_triples(self):
+        """All triples from one query share the same direction."""
+        t1 = _make_triple("a", "p1", "b")
+        t2 = _make_triple("a", "p2", "c")
+
+        call_count = 0
+
+        async def multi_results(**kwargs):
+            nonlocal call_count
+            call_count += 1
+            if call_count == 1:
+                return [t1, t2]
+            return []
+
+        client = AsyncMock()
+        client.query_stream = multi_results
+        query = _make_query(triples_client=client)
+
+        result = await query.execute_batch_triple_queries(
+            ["e1"], limit_per_entity=10
+        )
+
+        # First query (FROM_S) returns 2 triples, both should be FROM_S
+        assert len(result) == 2
+        assert result[0] == (t1, Query.FROM_S)
+        assert result[1] == (t2, Query.FROM_S)
+
 
 class TestLRUCacheWithTTL: