feat: add yaml_patcher service to apply LLM profiles to scenario YAML

tests/webapp/test_llm_profiles_api.py

@@ -65,3 +65,75 @@ def test_update_nonexistent(client):
 def test_delete_nonexistent(client):
     resp = client.delete("/api/llm-profiles/nope")
     assert resp.status_code == 404
+
+
+# ---------------------------------------------------------------------------
+# YAML patcher tests
+# ---------------------------------------------------------------------------
+import yaml as yaml_lib
+from webapp.services.yaml_patcher import apply_profiles_to_scenario
+from webapp.models import LLMProfile
+
+
+def test_apply_judge_profile(tmp_path):
+    """Applying a judge profile patches judge_model in the YAML."""
+    scenario_file = tmp_path / "test-scenario.yaml"
+    scenario_file.write_text(
+        "scenario_name: test\nmode: offline\njudge_model: old-model\nembedding_model: emb\n"
+        "dataset: data.csv\nmetrics:\n- faithfulness\noutput_dir: outputs/test\n",
+        encoding="utf-8",
+    )
+    judge_p = LLMProfile(
+        profile_id="x", name="J", model="new-model",
+        base_url="http://x/v1", api_key="k", created_at="t", updated_at="t",
+    )
+    patched = apply_profiles_to_scenario(
+        scenario_path=str(scenario_file),
+        judge_profile=judge_p,
+        answer_profile=None,
+        dataset_profile=None,
+        _resolve_absolute=True,
+    )
+    assert "judge_model" in patched
+    data = yaml_lib.safe_load(scenario_file.read_text())
+    assert data["judge_model"] == "new-model"
+
+
+def test_apply_answer_profile(tmp_path):
+    """Applying an answer profile patches app_adapter.static_kwargs.model."""
+    scenario_file = tmp_path / "online.yaml"
+    scenario_file.write_text(
+        "scenario_name: online\nmode: online\njudge_model: j\nembedding_model: emb\n"
+        "dataset: d.csv\nmetrics:\n- faithfulness\noutput_dir: out\n"
+        "app_adapter:\n  type: python\n  callable: apps.foo:run\n"
+        "  static_kwargs:\n    model: old\n    source_chunks_path: chunks.jsonl\n",
+        encoding="utf-8",
+    )
+    answer_p = LLMProfile(
+        profile_id="y", name="A", model="new-answer-model",
+        base_url="http://x/v1", api_key="k", created_at="t", updated_at="t",
+    )
+    patched = apply_profiles_to_scenario(
+        scenario_path=str(scenario_file),
+        judge_profile=None,
+        answer_profile=answer_p,
+        dataset_profile=None,
+        _resolve_absolute=True,
+    )
+    assert "app_adapter.static_kwargs.model" in patched
+    data = yaml_lib.safe_load(scenario_file.read_text())
+    assert data["app_adapter"]["static_kwargs"]["model"] == "new-answer-model"
+
+
+def test_apply_no_profiles_returns_empty(tmp_path):
+    """When no profiles are given, no fields are patched."""
+    scenario_file = tmp_path / "noop.yaml"
+    scenario_file.write_text("scenario_name: noop\njudge_model: m\n", encoding="utf-8")
+    patched = apply_profiles_to_scenario(
+        scenario_path=str(scenario_file),
+        judge_profile=None,
+        answer_profile=None,
+        dataset_profile=None,
+        _resolve_absolute=True,
+    )
+    assert patched == []