Skip fork-dependent integration tests when user namespaces unavailable

Signed-off-by: Cong Wang <cwang@multikernel.io>

Author: congwang-mk

tests/test_integration.py

@@ -13,11 +13,29 @@
 
 import pytest
 
+
+def _can_unshare_userns() -> bool:
+    """Check if the system supports unprivileged user namespaces."""
+    try:
+        result = subprocess.run(
+            ["unshare", "--user", "--map-root-user", "true"],
+            capture_output=True, timeout=5,
+        )
+        return result.returncode == 0
+    except (FileNotFoundError, subprocess.TimeoutExpired):
+        return False
+
+
 needs_branchfs = pytest.mark.skipif(
     not os.environ.get("BRANCHFS_MOUNT"),
     reason="BRANCHFS_MOUNT not set (no live branchfs)",
 )
 
+needs_userns = pytest.mark.skipif(
+    not _can_unshare_userns(),
+    reason="Kernel does not support unprivileged user namespaces",
+)
+
 
 @pytest.fixture
 def ws():
@@ -100,6 +118,7 @@ def test_sibling_branches_first_wins(ws):
 
 
 @needs_branchfs
+@needs_userns
 def test_speculate_parallel(ws):
     """Speculate runs candidates in parallel, commits the winner."""
     from branching import Speculate
@@ -121,6 +140,7 @@ def candidate_fail(path: Path) -> bool:
 
 
 @needs_branchfs
+@needs_userns
 def test_tree_of_thoughts_multi_level(ws):
     """TreeOfThoughts with expand commits accumulated state across levels."""
     from branching import TreeOfThoughts