fix: decouple system signal events from Telemetry (fixes #4041)

[devin-ai-integration]

fix: decouple system signal events from Telemetry (fixes #4041)

Summary

This PR fixes issue #4041 where system signal events (SigTermEvent, SigIntEvent, etc.) were disabled when telemetry was disabled via CREWAI_DISABLE_TELEMETRY=true.

The root cause was that signal registration logic lived entirely inside the Telemetry class, which returns early in __init__ when telemetry is disabled. This meant @on_signal handlers would never fire for users who opted out of telemetry.

Changes:

• Created new SystemSignalManager singleton class to handle OS signal registration independently of telemetry
• Signal handlers are now registered at system_events.py module import time, ensuring they work regardless of telemetry settings
• Telemetry now subscribes to signal events via the event bus for cleanup, rather than owning the signal handlers
• Added subprocess-based tests that verify signal events work with telemetry disabled

Review & Testing Checklist for Human

• Verify signal events fire with telemetry disabled: Run the reproduction script from issue [BUG] System signal events (SigTermEvent SigIntEvent) are disabled if Telemetry is disabled, and fragile to signal handler ordering #4041 with CREWAI_DISABLE_TELEMETRY=true and confirm @on_signal handlers execute
• Check handler chaining: Register a signal handler before importing CrewAI, then verify both handlers fire when signal is received
• Review the empty ensure_handlers_installed method at line 121 in signal_manager.py - it's defined but not implemented (just pass). Decide if this should be implemented or removed
• Test in multi-threaded context: Signal handlers can only be registered from the main thread - verify the warning logging works correctly when called from other threads
• Verify no import-time issues: The signal registration now happens at module import time - confirm this doesn't cause issues with test isolation or other import scenarios

Recommended test plan:

# Test script - save and run with CREWAI_DISABLE_TELEMETRY=true
import os
os.environ["CREWAI_DISABLE_TELEMETRY"] = "true"

from crewai.events.types.system_events import SignalEvent, on_signal

@on_signal
def my_handler(source, event):
    print(f"Signal received: {event.type}")

print(f"PID: {os.getpid()}")
# Then send SIGTERM from another terminal: kill -TERM <pid>

Notes

• Link to Devin run: https://app.devin.ai/sessions/4c13be5517f6450f855edc3b07ebf59e
• Requested by: João ([email protected])

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