Implement rec - Phase 4 complete

tests/ui/test_runtime_settings_store.py

@@ -107,6 +107,22 @@ def test_runtime_settings_uses_override_env_file(tmp_path: Path, monkeypatch):
     assert "PORT=9001" in target.read_text(encoding="utf-8")
 
 
+def test_runtime_settings_falls_back_to_shared_settings_env_file_override(tmp_path: Path, monkeypatch):
+    settings = _settings_for_runtime_editing(tmp_path)
+    target = tmp_path / "shared.env"
+    target.write_text("OPENROUTER_API_KEY=test-key\nPORT=8000\n", encoding="utf-8")
+    monkeypatch.delenv("RUNTIME_SETTINGS_ENV_FILE", raising=False)
+    monkeypatch.setenv("ENV_FILE", str(target))
+
+    snapshot = save_runtime_settings(
+        settings=settings,
+        updates={"port": "9001"},
+    )
+
+    assert snapshot.env_file_path == target
+    assert "PORT=9001" in target.read_text(encoding="utf-8")
+
+
 def test_save_runtime_settings_surfaces_unreadable_target(tmp_path: Path, monkeypatch):
     settings = _settings_for_runtime_editing(tmp_path)
     env_path = tmp_path / ".env"