selecting-reachable-grasp

poses is a list of Se3Pose, best first -- a propose skill's poses output, or the poses field of a GraspCandidates. It is declared here in prose rather than under required_inputs because the registry has no name for a bare list of poses, and a GraspCandidates is a dict the script does not take.

One strategy for the select stage: reachability, then clearance, first match wins.

Why this is its own skill

A proposer ranks by the object's geometry, which is the only thing it knows. Whether the arm can hold a pose is a different question, and entry 0 is routinely the one it cannot. Nothing downstream notices — IK returns something, the servo drives to it, and the jaws close on air. A study packet put it exactly: "gripper closed on nothing while grasping ring_spanner_19".

Taking the first that passes rather than the best: the list arrives ranked by a proposer that knows things about the object this skill does not, and re-ranking here would silently overrule it.

When to use

• After every propose rung. There is no case where taking candidate 0 unchecked is better than walking the list.

When NOT to use

• As a substitute for a collision-aware planner on the carry. This gates the grasp configuration, not the path to it. The two are different halves: a corridor test refuses a grasp whose descent goes through a shelf; a planner routes the carry around a beam. Neither substitutes for the other.

Recommended subgraph state flow

select → (selected | none_reachable)

A single script node. Inputs: poses (built from the proposer's stations and robot.grasp_frame's rotation), arm_id, object_name, check_clearance. Router on route.

Downstream, execute the selection with motion.plan_linear(orientation="lock") → robot.execute_trajectory so the closing heading is actually held — robot.go_to_pose leaves the wrist roll free and discards it.

Required end states

End state	Meaning
selected	pose and joint_config. Read index to see how far down the list it had to go, and corridor_checked to see whether clearance ran.
none_reachable	Nothing in the list solved. Route to another propose rung, not back to this one.