feat(s41): PORTFOLIO_MODEL_MAP override + placeholder fail-fast in resolve_model

tests/test_backends.py

@@ -1,5 +1,8 @@
 """Tests for the backend profiles (D2) — now wired (Fase 2), no longer skeletons."""
 
+import json
+from pathlib import Path
+
 import pytest
 from agent_framework import BaseChatClient
 
@@ -12,6 +15,19 @@ from portfolio_optimiser.backends import (
     resolve_model,
 )
 
+# A complete, non-placeholder map for the PORTFOLIO_MODEL_MAP override (S4.1). Both blocks are
+# required — resolve_model does no structural validation, so an azure-only map would break local.
+_VALID_MAP = {
+    "local": {"default": "qwen3:4b", "proposer": "qwen3:4b", "checker": "qwen3:4b"},
+    "azure": {"default": "gpt-4o-mini", "proposer": "gpt-4o-mini", "checker": "gpt-4o-mini"},
+}
+
+
+def _write_map(tmp_path: Path, data: dict) -> Path:
+    p = tmp_path / "model_map.json"
+    p.write_text(json.dumps(data), encoding="utf-8")
+    return p
+
 
 def test_get_backend_by_string() -> None:
     assert isinstance(get_backend("azure"), AzureFoundryBackend)
@@ -48,7 +64,34 @@ def test_azure_backend_fails_fast_without_endpoint(monkeypatch: pytest.MonkeyPat
         get_backend("azure").create_chat_client(model="dummy-deployment")
 
 
-def test_model_map_resolves_role_to_model() -> None:
+def test_model_map_resolves_role_to_model(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.delenv("PORTFOLIO_MODEL_MAP", raising=False)
     assert resolve_model("local", "proposer") == "qwen3:4b"
     # Unknown role falls back to the profile default (still a non-empty id).
     assert resolve_model(Profile.LOCAL, "no-such-role")
+
+
+def test_resolve_model_azure_placeholder_fails_fast(monkeypatch: pytest.MonkeyPatch) -> None:
+    # SC4: the bundled azure block ships REPLACE-WITH-* placeholders → never build a client from
+    # one. Detach point: remove the _PLACEHOLDER_PREFIX guard in resolve_model → this goes GREEN
+    # (returns the placeholder) → RED here.
+    monkeypatch.delenv("PORTFOLIO_MODEL_MAP", raising=False)
+    with pytest.raises(ValueError, match="placeholder"):
+        resolve_model("azure", "proposer")
+
+
+def test_resolve_model_override_redirects_azure(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    # SC5: PORTFOLIO_MODEL_MAP points at an out-of-tree valid map → resolves the real id (control:
+    # the raise fires only on the placeholder, not always). The committed model_map.json is never
+    # touched.
+    monkeypatch.setenv("PORTFOLIO_MODEL_MAP", str(_write_map(tmp_path, _VALID_MAP)))
+    assert resolve_model("azure", "proposer") == "gpt-4o-mini"
+    assert resolve_model("local", "proposer") == "qwen3:4b"
+
+
+def test_resolve_model_override_missing_file_fails_fast(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("PORTFOLIO_MODEL_MAP", "/nonexistent/model_map.json")
+    with pytest.raises(FileNotFoundError):
+        resolve_model("azure", "proposer")