Immersive Portals - CE 6.1.3.1

Minecraft 1.21.1 / NeoForge 21.1.228+ / Java 21

Fixed

• Fix the Sable startup crash caused by MixinClientboundStartTrackingSubLevelPacket_SablePortalCompat referencing the excluded SableInterpolationHistoryProbe class. Mixin resolves method owners before evaluating the disabled diagnostic branch.
• Route optional interpolation diagnostics through a packaged observer interface. The shared E2E client lifecycle installs its preservation oracle before either the rider or ship driver can connect, keeping the existing graft checks while production has no dependency on test drivers.

Verification

• JUnit inspects every compiled class in the actual release jar for references to excluded GameTests, asserts the observer and affected mixin are packaged, and rejects a generated reproduction of the original missing-helper invocation.
• Existing Sable integration and renderer CI remain required. Test results are reported in the pull request; these notes do not imply release publication.