Slabbed

First NeoForge build since 0.4.2-beta.2, so this is a big one — everything below has landed on the 1.21.1 NeoForge line since that release.

Placement is permanent

• The exact half-step you place a block at is stored, saved with its chunk, sent to clients, and stays put through neighbour updates and having its support removed.
• Blocks can seat as deep as -3.0; aims and landings deeper than that are refused before anything is changed.
• Server-side shape resolution is guarded off-thread, so background lighting and worldgen workers can't trigger chunk loads.

Rendering and physics agree with each other

• Model, outline, crosshair targeting, collision, culling and client refresh all resolve from one height number, right down to the -3.0 boundary.
• Inventory models, custom renderers, dynamic models and other mods' composite models keep their own identity — Slabbed no longer wraps models it doesn't own.
• Fences, walls and panes re-settle with each other immediately after a lowered placement, without cascading unrelated neighbour updates.

Sight, projectiles and blast

• Arrows, spectral arrows and tridents hit the drawn shape of a lowered block instead of its old full-height box.
• Mobs can't see you through a lowered block's visibly solid half.
• Explosion cover is measured against drawn shapes.
• And the reverse: the space a lowered block has visibly vacated is clear — arrows fly through it, mobs see through it, blasts reach through it.
• Kill switches if you need them: -Dslabbed.arrowOffsetClip=false, -Dslabbed.sightOffsetClip=false.

Compatibility and vanilla ownership

• Placed Terrain Slabs slabs behave like vanilla slabs — same locked-in heights, seating, cantilevering, stacking and support. Naturally generated Terrain Slabs terrain is deliberately left alone, which is what keeps terrain free of see-through seams.
• Create inventory models keep their identity while world models stay eligible for Slabbed rendering.
• Redstone connections and free-floating chain survival return to vanilla behaviour; mobs no longer spawn on bottom-like slab surfaces.
• Flower pots keep vanilla survival — breaking the block under a placed pot no longer destroys it.
• Integration coverage added for Terrain Slabs, Sable, Snow! Real Magic and Smooth Steps.

Deep mode (opt-in, per save)

• /slabbed deep-mode status|enable|confirm|cancel, owner-level, with a confirmation window and one-way activation for that save. New and existing worlds stay shallow by default, and unknown data fails closed.

Upgrade note

Blocks that follow a lowered support but were placed before the flush-landing rule will seat flush on the real surface the first time you load. That's a one-time visual shift to the intended position, not data loss.

Known limitations

• Mob path planning, Breeze aim, long-jump clearance and firework blasts still measure the unlowered box.
• Placing against a deeply lowered surface can briefly show the block at vanilla height before it drops to the correct landing. The final position is right.

258 required GameTests pass on a clean run. Alpha — please report anything odd!