"Deep vertical terrain sink defeats lateral eject and mantle — hard-recover to last grounded position"

The character sinks straight down through terrain at a chunk-corner seam — no lateral motion, just vertical burial. The body free-falls at a fixed XY position while containment systems fire and fail repeatedly: lateral eject restores to the same buried column, escape mantle refuses because the burial (2–3 m) exceeds its rise cap, and the global fall-recovery net (continuous air + distance threshold) never triggers because the eject ping-pong flickers Air↔Ground, resetting the continuous-air timer. The player eventually falls out the bottom of the world.

Two containment paths both fail on a deep stationary vertical sink:

1. Lateral eject restores to lastGoodPos, but with no lateral glide that anchor IS the same buried column. The restore re-buries the body and MarkUnburied re-banks the buried position as "good" — a self-referential anchor loop.

2. Escape mantle (bounded upward push) refuses because the burial depth (2–3 m) exceeds its rise cap (~1.2 m). It's tuned for shallow penetration, not deep burial.

The coarse sub-terrain fall-recovery net (5 s continuous Air + 25 m drop) can't catch it either: the eject ping-pong between Air and Ground resets the timer each cycle, and a 2–3 m surface trap is far short of the 25 m threshold.

Each containment rule was tuned for lateral glide-through penetration (the common case). A vertical sink at a seam is the orthogonal entry geometry that silently defeats all of them.

When a sustained burial is deep (exceeds the mantle rise cap) AND the eject give-back is degenerate (horizontal displacement between current position and anchor < ~0.75 m — sinking in place, not gliding), skip the futile lateral eject and hard-recover to lastGroundedPos — the last genuinely grounded position, a known-standable spot the body stood on a moment ago. Zero velocity, stay in Air state to re-land cleanly.

A real through-glide (metres of lateral travel) keeps the cheap lateral eject; only the stationary vertical sink escalates to hard-recover.

The hard-recover position is guaranteed to be standable — it's the same anchor used by the proven fall-recovery/unstuck system. By detecting the degenerate case (sinking in place with no lateral motion to reverse) and escalating to a known-good prior pose, the containment loop has a terminal exit that doesn't depend on the entry geometry that put the body there. The general rule: every penetration-containment loop needs a guaranteed-safe terminal recovery, not just geometry-specific fixes — and a coarse global kill-plane net is not a substitute for a fine-grained surface trap backstop.