nav-descend

name	nav-descend
type	python
description	Attempt exactly ONE controlled descent forward into an adjacent lower cell. Covers stepping down slopes, edges, and shallow drops (≤ 1 block).
schema_hint	{"value":"ignored","step_duration":"float seconds for the move (default: 0.25)","max_drop":"float maximum allowed drop in Y (default: 1.2)","min_drop":"float minimum Y decrease to count as descend (default: 0.2)","out":"$variable"}
examples	["{\"type\":\"nav-descend\",\"out\":\"$descend\"}"]

nav-descend

Attempt exactly ONE controlled descent forward into an adjacent lower cell. Covers stepping down slopes, edges, and shallow drops (≤ 1 block).

Input

• step_duration: Float seconds for the move (default: 0.25)
• max_drop: Float maximum allowed drop in Y (default: 1.2)
• min_drop: Float minimum Y decrease to count as descend (default: 0.2)

Output

Success (status: "success"):

• value: Summary text
• extra.from: Starting position {x, y, z}
• extra.to: Ending position {x, y, z}
• extra.delta_y: Vertical displacement (negative, within bounds)
• extra.support_here: Support type at destination

Failure (status: "failed"):

• reason: One of "status_failed", "move_failed", "collision", "observation_failed", "support_ambiguous", "no_descent", "excessive_drop"

Invariants

• Automatically aligns agent to block center and cardinal yaw before descent attempt
• Exactly one descent attempt per call (always forward, relative to current yaw)
• Descent must be within bounds: min_drop ≤ |delta_y| ≤ max_drop
• Landing support must be walkable ("solid" or "unsafe")
• Snaps to block center after any position change
• Updates world_state("nav") history

Alignment

Before descent attempt, agent is automatically aligned:

• Position: Block center (x+0.5, y, z+0.5) - eliminates fractional offsets
• Yaw: Nearest cardinal (0°=South, 90°=West, 180°=North, 270°=East)
• Pitch: 0°

This prevents collisions from fractional offsets and ensures predictable forward direction.

Planning Notes

• Does not handle multi-block drops; compose multiple calls for that
• Use nav-turn before descending to change direction (yaw determines forward direction)
• Alignment to block center and cardinal yaw happens automatically (no manual alignment needed)
• Falls within bounds are treated as controlled descent (success if landing is safe)

Example Workflow

{"type":"nav-turn","direction":"left","out":"$t"}
{"type":"nav-descend","out":"$d1"}
{"type":"nav-descend","out":"$d2"}