The viewer currently renders alpha in two separate passes: rigged alpha first, grouped by avatar pointer, followed by unrigged alpha back-to-front. Since most avatar alpha is rigged and most world alpha is not, the two cannot be ordered against each other. This causes familiar failures such as foreground hair rejecting trees behind it, while pointer-based avatar ordering can also differ between viewers.

This PR interleaves both streams in one back-to-front walk. Avatars and standalone animesh are keyed from their animated extents, while rigged attachments retain attachment-slot order. Non-HUD unrigged attachments inherit the wearer’s depth, so an avatar drains as one block: rigged first, followed by its unrigged groups back-to-front. This preserves the ordering content has historically been authored against within an avatar while giving the avatar a meaningful position among world alpha. Avatar depth lives in a dedicated mAvatarDepth key; the existing bounds-derived mDepth remains unchanged for world alpha and ordering within an attachment. Exact-depth ties use explicit ordering, with pointer identity only as the final tie-breaker.

Interleaving is enabled by RenderInterleavedAlpha for the normal post-water world pass. Pre-water, HUD, shadow, reflection, cube and other special renders retain the legacy ordering. Disabling the setting restores the legacy two-pass rendering path.

QA note: Feature-off is not byte-for-byte identical to upstream ordering. Attachment stamps now fan out from a bridge to every alpha group in its linkset, so multi-group rigged attachments can sort differently and more consistently, even with interleaving disabled. Stamps on unrigged groups are inert in the legacy world sort.