fix: annotate clusters and substitute {disputes} in classic pipeline path

tests/agents/test_classic_constructability_disputes.py

@@ -0,0 +1,51 @@
+"""Classic pipeline path must also satisfy the {disputes} placeholder added to
+CONSTRUCTABILITY_USER_INSTRUCTION (agent path substitutes it in construct_agent.py;
+the classic stage builds its own subs dict)."""
+
+from unittest.mock import patch
+
+from backend.pipeline._stage import render
+from backend.pipeline.constructability import constructability_review
+from backend.prompts import CONSTRUCTABILITY_USER_INSTRUCTION
+
+
+def _cluster_with_dispute():
+    return {
+        "key": "c1",
+        "assertions": [],
+        "disputed_attributes": [{
+            "attribute": "stud_pack_size",
+            "values": ["(2) 2x6 STUD PACK", "(5) 2x6 STUD PACK"],
+            "assertion_ids": ["a1", "a2"],
+        }],
+    }
+
+
+def test_classic_constructability_supplies_disputes_sub():
+    captured = {}
+
+    def fake_call_stage(system_prompt, user_instruction, subs=None, **kwargs):
+        captured["subs"] = subs or {}
+        return {"issues": []}
+
+    with patch("backend.pipeline.constructability.call_stage", fake_call_stage):
+        constructability_review([], [_cluster_with_dispute()], [])
+
+    assert "disputes" in captured["subs"], "classic path must substitute {disputes}"
+    rendered = render(CONSTRUCTABILITY_USER_INSTRUCTION, captured["subs"])
+    assert "{disputes}" not in rendered
+    assert "(5) 2x6 STUD PACK" in rendered
+
+
+def test_classic_constructability_disputes_defaults_empty():
+    captured = {}
+
+    def fake_call_stage(system_prompt, user_instruction, subs=None, **kwargs):
+        captured["subs"] = subs or {}
+        return {"issues": []}
+
+    with patch("backend.pipeline.constructability.call_stage", fake_call_stage):
+        constructability_review([], [{"key": "c2", "assertions": []}], [])
+
+    rendered = render(CONSTRUCTABILITY_USER_INSTRUCTION, captured["subs"])
+    assert "{disputes}" not in rendered