fix(hooks): arm the rebuild timeout without SIGALRM on Windows

The GRAPHIFY_REBUILD_TIMEOUT watchdog in both embedded rebuild bodies was
guarded by hasattr(signal, 'SIGALRM') with no else branch, so on Windows it
never armed and a hung rebuild survived indefinitely -- the exact tail case
the #791 timeout was added to catch.

Fall back to a daemon threading.Timer that prints the same message and calls
os._exit(1). The hard exit is deliberate: the process is already stuck, so a
clean shutdown may itself be blocked, and _rebuild_lock degrades to a no-op
yield on platforms without fcntl, so there is no lock to leave stale.

graphify/hooks.py

@@ -104,7 +104,7 @@ fi
 # double-quote, $, backtick or backslash characters: it is carried inside a
 # shell double-quoted `-c "..."` argument (see _detached_launch).
 _REBUILD_BODY_COMMIT = """\
-import os, signal, sys
+import os, signal, sys, threading
 from pathlib import Path
 
 changed_raw = os.environ.get('GRAPHIFY_CHANGED', '')
@@ -119,9 +119,17 @@ try:
     from graphify.watch import _rebuild_code, _apply_resource_limits
     _apply_resource_limits()
     _timeout = int(os.environ.get('GRAPHIFY_REBUILD_TIMEOUT', '600'))
-    if _timeout > 0 and hasattr(signal, 'SIGALRM'):
-        signal.signal(signal.SIGALRM, lambda *_: (_ for _ in ()).throw(TimeoutError(f'graphify rebuild exceeded {_timeout}s')))
-        signal.alarm(_timeout)
+    if _timeout > 0:
+        if hasattr(signal, 'SIGALRM'):
+            signal.signal(signal.SIGALRM, lambda *_: (_ for _ in ()).throw(TimeoutError(f'graphify rebuild exceeded {_timeout}s')))
+            signal.alarm(_timeout)
+        else:
+            def _bail():
+                print(f'[graphify hook] graphify rebuild exceeded {_timeout}s', flush=True)
+                os._exit(1)
+            _watchdog = threading.Timer(_timeout, _bail)
+            _watchdog.daemon = True
+            _watchdog.start()
     _force = os.environ.get('GRAPHIFY_FORCE', '').lower() in ('1', 'true', 'yes')
     _root = Path('.')
     _out = os.environ.get('GRAPHIFY_OUT', 'graphify-out')
@@ -153,13 +161,21 @@ except Exception as exc:
 _REBUILD_BODY_CHECKOUT = """\
 from graphify.watch import _rebuild_code, _apply_resource_limits
 from pathlib import Path
-import os, signal, sys
+import os, signal, sys, threading
 try:
     _apply_resource_limits()
     _timeout = int(os.environ.get('GRAPHIFY_REBUILD_TIMEOUT', '600'))
-    if _timeout > 0 and hasattr(signal, 'SIGALRM'):
-        signal.signal(signal.SIGALRM, lambda *_: (_ for _ in ()).throw(TimeoutError(f'graphify rebuild exceeded {_timeout}s')))
-        signal.alarm(_timeout)
+    if _timeout > 0:
+        if hasattr(signal, 'SIGALRM'):
+            signal.signal(signal.SIGALRM, lambda *_: (_ for _ in ()).throw(TimeoutError(f'graphify rebuild exceeded {_timeout}s')))
+            signal.alarm(_timeout)
+        else:
+            def _bail():
+                print(f'[graphify hook] graphify rebuild exceeded {_timeout}s', flush=True)
+                os._exit(1)
+            _watchdog = threading.Timer(_timeout, _bail)
+            _watchdog.daemon = True
+            _watchdog.start()
     _force = os.environ.get('GRAPHIFY_FORCE', '').lower() in ('1', 'true', 'yes')
     # post-checkout: branch switch can touch arbitrary files; full rebuild path
     # (no changed_paths) is correct here. The flock inside _rebuild_code still

tests/test_hooks.py

@@ -330,6 +330,26 @@ def test_rebuild_bodies_with_graphify_root_are_valid_python():
         ast.parse(body)
 
 
+@pytest.mark.parametrize(
+    "name,body",
+    [("post-commit", _REBUILD_BODY_COMMIT), ("post-checkout", _REBUILD_BODY_CHECKOUT)],
+)
+def test_rebuild_bodies_arm_a_timeout_without_sigalrm(name, body):
+    """Windows has no signal.SIGALRM, so the #791 rebuild timeout never armed
+    there at all (#2148). The fallback has to sit in the else-branch of the
+    SIGALRM check rather than merely appear somewhere in the body, so that a
+    watchdog firing unconditionally or on every platform still fails here."""
+    fallbacks = [
+        node.orelse
+        for node in ast.walk(ast.parse(body))
+        if isinstance(node, ast.If) and "'SIGALRM'" in ast.dump(node.test) and node.orelse
+    ]
+    assert fallbacks, f"{name} has no else-branch for the missing-SIGALRM case (#2148)"
+    dumped = "".join(ast.dump(stmt) for stmt in fallbacks[0])
+    assert "attr='Timer'" in dumped, f"{name} fallback does not arm a threading.Timer (#2148)"
+    assert "attr='_exit'" in dumped, f"{name} fallback does not kill the stuck rebuild (#2148)"
+
+
 def test_detached_launch_targets_graphify_python():
     """The launcher must run via the resolved $GRAPHIFY_PYTHON, not a bare
     `python`, so it uses the same interpreter the detection block selected."""