fix: handle missing signals on Windows (SIGHUP, SIGTSTP, SIGCONT)

This fixes GitHub issue #4062 where crewai crashes on Windows with
'module signal has no attribute SIGHUP' error.

Changes:
- Use getattr with fallback values for signals not available on Windows
- Make telemetry signal registration conditional on signal availability
- Add regression tests for Windows compatibility

The fix maintains backward compatibility on Unix systems while allowing
crewai to work on Windows where SIGHUP, SIGTSTP, and SIGCONT are not
available.

Co-Authored-By: João <joao@crewai.com>

lib/crewai/src/crewai/events/types/system_events.py

@@ -14,14 +14,25 @@ from pydantic import Field, TypeAdapter
 from crewai.events.base_events import BaseEvent
 
 
+# Fallback values for signals not available on Windows.
+# These are negative to avoid conflicts with real signal numbers.
+_FALLBACK_SIGHUP = -1
+_FALLBACK_SIGTSTP = -2
+_FALLBACK_SIGCONT = -3
+
+
 class SignalType(IntEnum):
-    """Enumeration of supported system signals."""
+    """Enumeration of supported system signals.
+
+    Note: SIGHUP, SIGTSTP, and SIGCONT are not available on Windows.
+    On Windows, these will use fallback negative values.
+    """
 
     SIGTERM = signal.SIGTERM
     SIGINT = signal.SIGINT
-    SIGHUP = signal.SIGHUP
-    SIGTSTP = signal.SIGTSTP
-    SIGCONT = signal.SIGCONT
+    SIGHUP = getattr(signal, "SIGHUP", _FALLBACK_SIGHUP)
+    SIGTSTP = getattr(signal, "SIGTSTP", _FALLBACK_SIGTSTP)
+    SIGCONT = getattr(signal, "SIGCONT", _FALLBACK_SIGCONT)
 
 
 class SigTermEvent(BaseEvent):

lib/crewai/src/crewai/telemetry/telemetry.py

@@ -172,11 +172,21 @@ class Telemetry:
 
         self._original_handlers: dict[int, Any] = {}
 
+        # Always-supported signals on all platforms
         self._register_signal_handler(signal.SIGTERM, SigTermEvent, shutdown=True)
         self._register_signal_handler(signal.SIGINT, SigIntEvent, shutdown=True)
-        self._register_signal_handler(signal.SIGHUP, SigHupEvent, shutdown=False)
-        self._register_signal_handler(signal.SIGTSTP, SigTStpEvent, shutdown=False)
-        self._register_signal_handler(signal.SIGCONT, SigContEvent, shutdown=False)
+
+        # Optional signals (not available on Windows)
+        optional_signals: list[tuple[str, type, bool]] = [
+            ("SIGHUP", SigHupEvent, False),
+            ("SIGTSTP", SigTStpEvent, False),
+            ("SIGCONT", SigContEvent, False),
+        ]
+
+        for sig_name, event_class, shutdown in optional_signals:
+            sig = getattr(signal, sig_name, None)
+            if sig is not None:
+                self._register_signal_handler(sig, event_class, shutdown=shutdown)
 
     def _register_signal_handler(
         self,

lib/crewai/tests/events/types/test_system_events.py

@@ -24,13 +24,26 @@ class TestSignalType:
     """Tests for SignalType enum."""
 
     def test_signal_type_values(self) -> None:
-        """Verify SignalType maps to correct signal numbers."""
+        """Verify SignalType maps to correct signal numbers when available."""
         assert SignalType.SIGTERM == signal.SIGTERM
         assert SignalType.SIGINT == signal.SIGINT
+
+        # These signals are not available on Windows, so only check if present
+        if hasattr(signal, "SIGHUP"):
             assert SignalType.SIGHUP == signal.SIGHUP
+        if hasattr(signal, "SIGTSTP"):
             assert SignalType.SIGTSTP == signal.SIGTSTP
+        if hasattr(signal, "SIGCONT"):
             assert SignalType.SIGCONT == signal.SIGCONT
 
+    def test_signal_type_enum_members_always_exist(self) -> None:
+        """Verify all SignalType enum members exist regardless of platform."""
+        assert hasattr(SignalType, "SIGTERM")
+        assert hasattr(SignalType, "SIGINT")
+        assert hasattr(SignalType, "SIGHUP")
+        assert hasattr(SignalType, "SIGTSTP")
+        assert hasattr(SignalType, "SIGCONT")
+
 
 class TestSignalEvents:
     """Tests for individual signal event classes."""
@@ -195,3 +208,70 @@ class TestSignalEventSerialization:
         assert isinstance(restored, SigTermEvent)
         assert restored.reason == original.reason
         assert restored.type == original.type
+
+
+class TestWindowsCompatibility:
+    """Tests for Windows compatibility (signals not available on Windows)."""
+
+    def test_system_events_imports_when_optional_signals_missing(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        """system_events should import even if some signals are missing (Windows-like).
+
+        This is a regression test for GitHub issue #4062.
+        """
+        import importlib
+
+        import crewai.events.types.system_events as system_events_module
+
+        # Simulate a Windows-like signal module by removing optional signals
+        monkeypatch.delattr(signal, "SIGHUP", raising=False)
+        monkeypatch.delattr(signal, "SIGTSTP", raising=False)
+        monkeypatch.delattr(signal, "SIGCONT", raising=False)
+
+        # Reload after patching so class definitions see the modified signal module
+        reloaded = importlib.reload(system_events_module)
+
+        # Import should succeed and enum members should exist
+        assert hasattr(reloaded.SignalType, "SIGHUP")
+        assert hasattr(reloaded.SignalType, "SIGTSTP")
+        assert hasattr(reloaded.SignalType, "SIGCONT")
+
+        # Event classes should still be importable
+        assert hasattr(reloaded, "SigHupEvent")
+        assert hasattr(reloaded, "SigTStpEvent")
+        assert hasattr(reloaded, "SigContEvent")
+
+        # Fallback values should be negative (to avoid conflicts with real signals)
+        assert reloaded.SignalType.SIGHUP < 0
+        assert reloaded.SignalType.SIGTSTP < 0
+        assert reloaded.SignalType.SIGCONT < 0
+
+    def test_signal_events_can_be_created_when_signals_missing(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        """Signal events should be creatable even when signals are missing.
+
+        This is a regression test for GitHub issue #4062.
+        """
+        import importlib
+
+        import crewai.events.types.system_events as system_events_module
+
+        # Simulate a Windows-like signal module
+        monkeypatch.delattr(signal, "SIGHUP", raising=False)
+        monkeypatch.delattr(signal, "SIGTSTP", raising=False)
+        monkeypatch.delattr(signal, "SIGCONT", raising=False)
+
+        # Reload after patching
+        reloaded = importlib.reload(system_events_module)
+
+        # Events should be creatable
+        hup_event = reloaded.SigHupEvent()
+        assert hup_event.type == "SIGHUP"
+
+        tstp_event = reloaded.SigTStpEvent()
+        assert tstp_event.type == "SIGTSTP"
+
+        cont_event = reloaded.SigContEvent()
+        assert cont_event.type == "SIGCONT"

lib/crewai/tests/telemetry/test_telemetry.py

@@ -1,4 +1,5 @@
 import os
+import signal
 import threading
 from unittest.mock import patch
 
@@ -121,3 +122,36 @@ def test_telemetry_singleton_pattern():
         thread.join()
 
     assert all(instance is telemetry1 for instance in instances)
+
+
+def test_telemetry_register_shutdown_handlers_with_missing_optional_signals(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Telemetry shouldn't fail when optional signals are missing (Windows-like).
+
+    This is a regression test for GitHub issue #4062.
+    """
+    import importlib
+
+    from crewai.telemetry import telemetry as telemetry_module
+
+    # Disable telemetry to avoid real OTLP setup
+    monkeypatch.setenv("CREWAI_DISABLE_TELEMETRY", "true")
+
+    # Simulate a Windows-like signal module by removing optional signals
+    monkeypatch.delattr(signal, "SIGHUP", raising=False)
+    monkeypatch.delattr(signal, "SIGTSTP", raising=False)
+    monkeypatch.delattr(signal, "SIGCONT", raising=False)
+
+    # Reload after patching so the module sees the modified signal module
+    reloaded = importlib.reload(telemetry_module)
+
+    # Reset the singleton to allow a new instance
+    reloaded.Telemetry._instance = None
+    reloaded.Telemetry._lock = threading.Lock()
+
+    # This should not raise an error even with missing signals
+    telemetry = reloaded.Telemetry()
+
+    # Telemetry should be disabled (due to env var), but import should succeed
+    assert telemetry.ready is False