bug: Race conditions and deadlock possible in embeddings/basic.py

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Python version (python --version)

Python 3.13.2

Operating system/version

MacOS Tahoe 26.0.1

NeMo-Guardrails version (if you must use a specific version and not the latest

latest

Describe the bug

While reviewing #1383, several possible race and deadlock conditions were identified in the embeddings/basic.py file:

• Indentation can cause deadlock.
• Missing lock on self._current_batch_finished_event can cause hangs.
• Initialization of events may create spurious RuntimeError

Steps To Reproduce

Identified statically from code analysis

Expected Behavior

Expect embeddings index not to hang or deadlock

Actual Behavior

Possible hang and/or deadlock when building index

Inspect embeddings/basic.py and the three linked discussions from pull request #1383, starting with the event and locking logic involved in index construction. Verify the identified race and deadlock paths under concurrent index building; done means embeddings index construction no longer hangs, deadlocks, or raises spurious RuntimeError.