Delete the callerless portal-BFS research graph and spent renderer probe families while retaining the production RetailFrameWalk path, terrain diagnostics, membership invariant, and walk transcript.
Mutation evidence (all restored):
1. Restored PortalVisibilityBuilder type -> AppAssembly_ContainsNoSupersededPortalGraphTypes first failed Assert.Empty with AcDream.App.Rendering.PortalVisibilityBuilder.
2. Restored ACDREAM_PROBE_FACILITY_STAIRS -> ProductionSource_ContainsNoDeletedRendererProbe_AndRetainsWalkTranscriptProof first failed Assert.Empty on RenderingDiagnostics.cs.
3. Added a second RetailFrameWalk field -> WalkFrameOwners_AreUnique first failed Assert.Single with _frameWalk and _mutatedSecondFrameWalk.
4. Added OrderBy to OrderedStream -> OrderedWalkStream_HasNoCrossStreamReorder first failed Assert.DoesNotContain on OrderBy(.
5. Added IDatReaderWriter parameter -> FrameTimeWalkOwners_HaveNoRawDatDependency first failed Assert.Empty on RetailFrameWalk.MutatedRawDatParameter.
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