Prevent NPE for weightless contraptions

[lap2ka]

Fix #457, fix #478, fix #851, fix #882, fix #906, fix #909
lotta duplicates here

[Copilot]

Pull request overview

This PR targets a recurring server crash in the Create compatibility layer where MassTracker.getCenterOfMass() can be null for certain “weightless” / non-solid contraptions, leading to a NullPointerException during contraption initialization.

Changes:

• Adds a null-check before translating floating block cluster origins using the contraption center of mass.
• Adds a null-check before adding the contraption to the physics pipeline.

Comments suppressed due to low confidence (1)

neoforge/src/main/java/dev/ryanhcode/sable/neoforge/mixin/compatibility/create/contraptions/AbstractContraptionEntityMixin.java:175

• This null-guard prevents the immediate NPE, but leaves sable$massTracker in a state where getCenterOfMass() is null. Several call sites assume a non-null center of mass (e.g., KinematicContraption.sable$getLocalPose() and this mixin's sable$getPosition()), so if this contraption is added to a plot or the physics pipeline later it can still crash. Consider treating a null centerOfMass as an invalid MassTracker and explicitly skipping/removing the contraption from any physics/plot collections (or providing a safe fallback center of mass) to keep invariants consistent.

        assert this.sable$localBounds != null;
        this.sable$massTracker = MassTracker.build(this.sable$blockGetter(), this.sable$localBounds);
        final Vector3dc centerOfMass = this.sable$massTracker.getCenterOfMass();
        if (centerOfMass != null) {
            final Vector3d temp = centerOfMass.negate(new Vector3d()).add(0.5, 0.5, 0.5);
            for (final FloatingBlockCluster cluster : this.sable$floatingClusterContainer.clusters) {
                cluster.getBlockData().translateOrigin(temp);
            }
        }

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[lap2ka]

shi the AI overlord is right

[lap2ka]