merge: T57 significance-aware retrieval ranking

tests/test_memory_search.py

@@ -125,3 +125,37 @@ def test_search_invalid_witness_role_raises(tmp_path):
     with open_db(db) as conn:
         with pytest.raises(ValueError):
             search_memories(conn, "bot_a", "invalid_role", "anything", k=4)
+
+
+def test_higher_significance_outranks_equal_rank(tmp_path):
+    """T57: significance multiplier biases the SQL ORDER BY.
+
+    Two memories with IDENTICAL FTS-matching text yield (effectively) equal
+    BM25 ranks. The significance bias applied in the SQL ORDER BY must
+    surface the higher-significance row first.
+    """
+    db = tmp_path / "t.db"
+    _seed(
+        db,
+        memory_specs=[
+            # Identical pov_summary text -> FTS BM25 rank is the same for both.
+            {"pov_summary": "she swore an oath", "significance": 0},
+            {"pov_summary": "she swore an oath", "significance": 3},
+        ],
+    )
+    with open_db(db) as conn:
+        out = search_memories(conn, "bot_a", "host", "oath", k=5)
+        assert len(out) == 2
+        # Higher significance wins despite tied FTS rank.
+        assert out[0]["significance"] == 3
+        assert out[1]["significance"] == 0
+
+
+def test_significance_bias_is_constant_module_level():
+    """T57: pin ``SIGNIFICANCE_RANK_BIAS`` as a tunable module-level numeric."""
+    from chat.state.memory import SIGNIFICANCE_RANK_BIAS
+
+    assert isinstance(SIGNIFICANCE_RANK_BIAS, (int, float))
+    # Must be non-negative -- a negative bias would invert the desired
+    # "higher significance ranks higher" semantics.
+    assert SIGNIFICANCE_RANK_BIAS >= 0