feat(zerogpu): decorate() shim for HF ZeroGPU compatibility

server/zerogpu.py

@@ -0,0 +1,25 @@
+"""ZeroGPU decorator shim.
+
+When `spaces` is importable (HF ZeroGPU runtime), `decorate` wraps
+functions with `spaces.GPU(duration=...)`. Otherwise it is the
+identity decorator. Local installs and Free CPU Spaces hit the
+no-op branch.
+"""
+from __future__ import annotations
+
+from typing import Callable, TypeVar
+
+
+F = TypeVar("F", bound=Callable)
+
+
+try:  # pragma: no cover — covered by a test that injects a fake module
+    import spaces  # type: ignore[import-not-found]
+
+    def decorate(fn: F) -> F:
+        return spaces.GPU(duration=120)(fn)  # type: ignore[no-any-return]
+
+except ImportError:  # local / Free CPU
+
+    def decorate(fn: F) -> F:
+        return fn

tests/test_zerogpu.py

@@ -0,0 +1,33 @@
+import sys
+from unittest.mock import MagicMock
+
+from server.zerogpu import decorate
+
+
+def test_decorate_is_passthrough_when_spaces_missing(monkeypatch):
+    monkeypatch.setitem(sys.modules, "spaces", None)
+
+    @decorate
+    def fn(x):
+        return x * 2
+
+    assert fn(3) == 6
+
+
+def test_decorate_uses_spaces_gpu_when_available(monkeypatch):
+    fake_spaces = MagicMock()
+    fake_decorator = MagicMock(side_effect=lambda f: f)
+    fake_spaces.GPU = MagicMock(return_value=fake_decorator)
+    monkeypatch.setitem(sys.modules, "spaces", fake_spaces)
+
+    import importlib
+    import server.zerogpu as zg
+
+    importlib.reload(zg)
+
+    @zg.decorate
+    def fn(x):
+        return x + 1
+
+    assert fn(2) == 3
+    fake_spaces.GPU.assert_called_once()