chore: import upstream snapshot with attribution

tests/test_backend_extras.py

@@ -0,0 +1,41 @@
+"""The claude backend must be installable via an extra, and the missing-package
+message must point uv-tool users at the right command.
+
+Friction this guards: `uv tool install graphifyy` puts graphify in an isolated
+venv. A user with ANTHROPIC_API_KEY set then hit "anthropic package required"
+with no extra to satisfy it (claude was the only backend with no `[extra]`), and
+the message said `pip install anthropic`, which does not reach a uv tool venv.
+"""
+from pathlib import Path
+
+from graphify.llm import _backend_pkg_hint
+
+try:
+    import tomllib
+except ModuleNotFoundError:  # Python 3.10
+    import tomli as tomllib  # type: ignore[no-redef]
+
+PYPROJECT = Path(__file__).resolve().parent.parent / "pyproject.toml"
+
+
+def _extras():
+    data = tomllib.loads(PYPROJECT.read_text(encoding="utf-8"))
+    return data["project"]["optional-dependencies"]
+
+
+def test_anthropic_extra_exists():
+    extras = _extras()
+    assert "anthropic" in extras, "claude backend needs a [anthropic] extra"
+    assert any("anthropic" in dep for dep in extras["anthropic"])
+
+
+def test_anthropic_in_all_extra():
+    extras = _extras()
+    assert any("anthropic" in dep for dep in extras["all"]), "[all] must include anthropic"
+
+
+def test_backend_pkg_hint_points_at_uv_tool_and_extra():
+    msg = _backend_pkg_hint("anthropic", "anthropic")
+    assert "uv tool install" in msg
+    assert 'graphifyy[anthropic]' in msg
+    assert "pip install anthropic" in msg  # pip/venv fallback still mentioned