Code-review follow-up to 003c502:
1. Test 3 (OnRemove_StopsScriptsAndEmitters) now wires the runner into
the real ParticleHookSink instead of a RecordingSink, registers a
persistent EmitterDesc, lets the CreateParticleHook actually spawn an
emitter, then asserts the sink killed it after OnRemove. Previously
the test only verified runner-side state — sink.StopAllForEntity was
never observably exercised, so a regression dropping that call would
have passed silently.
2. Removed unused `using System.Numerics` from EntityScriptActivator.cs.
No production code changes. Tests 1 and 2 unchanged.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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