context.signal_entity causes sub orchestrator to never finish.

🐛 **Describe the bug**
Using `context.signal_entity` causes a sub-orchestrator to never finish. That is, it prevents `StopIteration` from being raised.

🤔 **Expected behavior**
Signalling an entity does not cause the generator to fail

☕ **Steps to reproduce**
Create an entity and signal it from within a sub orchestrator. This will cause it to not finish. Now switch it to use `context.call_entity`, which works as expected.

Start by reproducing the minimal entity and sub-orchestrator case described, then compare the context.signal_entity and context.call_entity entry points while tracing how StopIteration completes the generator. Done means signaling the entity no longer prevents the sub-orchestrator from finishing, with regression coverage for the expected behavior.

Written by the indexing model from the issue text.