refactor(sampler): replace family_spec param with level+constraint

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/unit/test_sampler_v2.py

@@ -181,10 +181,11 @@ class TestSampleMaterialV2:
         rng = random.Random(42)
         result = sample_material_v2(
             tree=real_tree,
-            family_spec=RETRIEVAL_FAMILY,
             task_type="Action Reasoning",
             used_node_ids=set(),
             rng=rng,
+            level=2,
+            constraint=RETRIEVAL_FAMILY.sampling,
         )
 
         assert isinstance(result, MaterialContext)
@@ -213,10 +214,11 @@ class TestSampleMaterialV2:
 
         result = sample_material_v2(
             tree=real_tree,
-            family_spec=RETRIEVAL_FAMILY,
             task_type="Action Reasoning",
             used_node_ids=used,
             rng=rng,
+            level=2,
+            constraint=RETRIEVAL_FAMILY.sampling,
         )
 
         # 锚节点应该是那个未被排除的 L2
@@ -233,10 +235,11 @@ class TestSampleMaterialV2:
         with pytest.raises(RuntimeError, match="max_attempts"):
             sample_material_v2(
                 tree=sparse_tree,
-                family_spec=VISUAL_FAMILY,
                 task_type="Object Recognition",
                 used_node_ids=set(),
                 rng=rng,
+                level=3,
+                constraint=VISUAL_FAMILY.sampling,
                 max_attempts=3,
             )
 
@@ -248,10 +251,11 @@ class TestSampleMaterialV2:
 
         result = sample_material_v2(
             tree=real_tree,
-            family_spec=REASONING_FAMILY,
-            task_type="Causal Reasoning",
+            task_type="Action Reasoning",
             used_node_ids=set(),
             rng=rng,
+            level=2,
+            constraint=REASONING_FAMILY.sampling,
         )
 
         # cross_l2_span=True 时必须有跨 L2 文本
@@ -265,10 +269,11 @@ class TestSampleMaterialV2:
 
         result = sample_material_v2(
             tree=real_tree,
-            family_spec=RETRIEVAL_FAMILY,
             task_type="Action Reasoning",
             used_node_ids=set(),
             rng=rng,
+            level=2,
+            constraint=RETRIEVAL_FAMILY.sampling,
         )
 
         # real_tree 所有节点都有字幕，所以 subtitle_sentences 非空