Robot hearing dispatch

Entry point: hearing.launch.py.

Called from task_generator.launch.py's OpaqueFunction (once per environment, only when robot.hearing is not none, which needs acoustics:=arena) with frontend (the robot.hearing key), policy (robot.hearing.policy), namespace and environment_namespace. Every launch configuration of the parent stays visible to the backend, so undeclared robot.hearing.* keys reach it by prefix.

SelectAction dispatch

Key	Action
none	empty group, no nodes
bus, srp, seld	includes arena/arena.launch.py

arena backend

arena/arena.launch.py fails with the arena feature hearing install hint when the arena_hearing package is missing. Otherwise it includes arena_hearing's launch/hearing.launch.py in isolation with:

Arg	Value
robot.hearing.<key>	every non-empty one of the parent except robot.hearing.policy, the hearing launch strips the prefix
env.ns	absolute env namespace, the hearing nodes live in it
tg_node	task generator node name, the auditory topics live below it
frontend	robot.hearing
policy	robot.hearing.policy

robot.hearing.* keys never reach the task generator node or the robot adapters. The Nav2 speed-filter overlay comes from task_generator.simulators.hearing.nav2_overlay(hearing) (arena_hearing/config/nav2_overlay.yaml, empty for none) and lands as robot.mobile.params_overlay unless that is set explicitly.

Node side

task_generator/simulators/hearing/ holds HearingRegistry, keyed none|bus|srp|seld, yielding a BaseHearing: robot_displays(robot) (the robot's _hearing manifest entry: belief grid, speed mask, wedges) and recorded_topics(). simulators/hearing/arena/ is the only task_generator code importing arena_hearing.

Layout

launch/hearing/
|-- hearing.launch.py      dispatcher
`-- arena/
    `-- arena.launch.py    install check, shim into arena_hearing's hearing.launch.py