Add a Minimal Unit Test for RuntimeSignalBridge.build_event()

[kiyoshisasano]

📌 Summary

Create the first foundational test file validating expected behavior of event generation.

🎯 Why

Establishes a scaffold for future tests.

🛠 Scope

Create test file (e.g., tests/test_runtime_bridge.py)

Add a happy-path test validating a basic event is constructed correctly

No strict validation rules yet