Add 3 red tests for Phase 1: config-driven models

Tests that will pass once implemented:
- graph_has_models: graph definition includes MODELS dict
- instantiate_applies_graph_models: node.model set from graph config
- model_override_per_request: process_message accepts model_overrides

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

tests/test_engine.py

@@ -477,9 +477,60 @@ def test_frame_trace_expert_with_interpreter():
     assert trace["total_frames"] >= 5, f"expected >=5 frames, got {trace['total_frames']}"
 
 
+# --- Phase 1: Config-driven models (RED — will fail until implemented) ---
+
+def test_graph_has_models():
+    """Graph definition includes a MODELS dict mapping role → model."""
+    g = load_graph("v4-eras")
+    assert "models" in g, "graph should have a 'models' key"
+    models = g["models"]
+    assert isinstance(models, dict), "models should be a dict"
+    # Every LLM-using node should have a model entry
+    llm_nodes = {"input", "pa", "expert_eras", "interpreter", "output", "memorizer"}
+    for role in llm_nodes:
+        assert role in models, f"models should include '{role}'"
+        assert isinstance(models[role], str) and "/" in models[role], \
+            f"model for '{role}' should be a provider/model string, got {models.get(role)}"
+
+
+def test_instantiate_applies_graph_models():
+    """instantiate_nodes applies model from graph config, overriding class default."""
+    hud = MockHud()
+    g = load_graph("v4-eras")
+    # Override a model in graph config
+    g["models"] = g.get("models", {})
+    g["models"]["input"] = "test/override-model"
+    nodes = instantiate_nodes(g, hud)
+    assert nodes["input"].model == "test/override-model", \
+        f"input node model should be 'test/override-model', got {nodes['input'].model}"
+
+
+def test_model_override_per_request():
+    """Engine accepts model overrides that are applied to nodes for one request."""
+    nodes = {
+        "input": MockInputNode(intent="social", complexity="trivial"),
+        "output": MockOutputNode(),
+        "pa": MockPANode(),
+        "expert_eras": MockExpertNode(),
+        "interpreter": MockInterpreterNode(),
+        "memorizer": MockMemorizer(),
+        "sensor": MockSensor(),
+        "ui": MockUINode(),
+    }
+    engine, sink, hud = make_frame_engine(nodes, "v4-eras")
+
+    # process_message should accept model_overrides param
+    result = asyncio.get_event_loop().run_until_complete(
+        engine.process_message("hello", model_overrides={"input": "test/fast-model"})
+    )
+    # Should complete without error (overrides applied internally)
+    assert result["trace"]["path"] == "reflex"
+
+
 # --- Test registry (for run_tests.py) ---
 
 TESTS = {
+    # Green — engine mechanics
     'graph_load': test_graph_load,
     'node_instantiation': test_node_instantiation,
     'edge_types_complete': test_edge_types_complete,
@@ -488,4 +539,8 @@ TESTS = {
     'frame_trace_reflex': test_frame_trace_reflex,
     'frame_trace_expert': test_frame_trace_expert,
     'frame_trace_expert_with_interpreter': test_frame_trace_expert_with_interpreter,
+    # Red — Phase 1: config-driven models
+    'graph_has_models': test_graph_has_models,
+    'instantiate_applies_graph_models': test_instantiate_applies_graph_models,
+    'model_override_per_request': test_model_override_per_request,
 }