feat: Behavior tree coordinator for autonomous mode (Issue #482)

State machine: idle → patrol → investigate → interact → return
- IDLE: Waiting for activation or battery recovery
- PATROL: Autonomous patrolling with curiosity-driven exploration (#470)
- INVESTIGATE: Approach and track detected persons
- INTERACT: Social interaction with face recognition and gestures
- RETURN: Navigate back to home/dock with recovery behaviors

Integrations:
- Patrol mode (#446): Waypoint routes with geofence (#441)
- Curiosity behavior (#470): Autonomous exploration
- Person following: Approach detected persons
- Emergency stop cascade (#459): Highest priority safety
- Geofence constraint (#441): Keep patrol within boundaries

Blackboard variables:
- battery_level: Current battery percentage
- person_detected: Person detection state
- current_mode: Current behavior tree state
- home_pose: Home/dock location

Files:
- behavior_trees/autonomous_coordinator.xml: BehaviorTree definition
- launch/autonomous_mode.launch.py: Full launch setup
- saltybot_bringup/bt_nodes.py: Custom BT node plugins
- BEHAVIOR_TREE_README.md: Documentation

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

jetson/ros2_ws/src/saltybot_bringup/BEHAVIOR_TREE_README.md

@@ -0,0 +1,75 @@
+# SaltyBot Autonomous Behavior Tree Coordinator (Issue #482)
+
+## Overview
+
+Autonomous mode state machine with 5 states:
+```
+idle → patrol → investigate → interact → return → idle
+```
+
+## States
+
+### IDLE: Waiting/Charging
+- Robot stationary, waiting for activation
+- Timeout: 60 seconds
+- Transition: Moves to PATROL when activated
+
+### PATROL: Autonomous Patrolling
+- Executes waypoint routes within geofence (#441)
+- Integrates curiosity (#470) for autonomous exploration
+- Monitors for person detection
+- Battery check: Returns to IDLE if <20%
+
+### INVESTIGATE: Person Investigation
+- Approaches and tracks detected person (#212)
+- Fallback: Navigate to last known position
+- Transition: → INTERACT when person approached
+
+### INTERACT: Social Interaction
+- Face recognition and greeting
+- Gesture detection and response (#454)
+- Timeout: 30 seconds
+- Transition: → RETURN
+
+### RETURN: Return to Home/Dock
+- Navigates back to home pose
+- Nav2 recovery behaviors with retries
+- Transition: → IDLE when complete
+
+## Blackboard Variables
+
+```python
+battery_level: float          # Battery percentage (0-100)
+person_detected: bool         # Person detection state
+obstacle_state: str          # 'clear' | 'near' | 'blocked'
+current_mode: str            # State: idle/patrol/investigate/interact/return
+home_pose: PoseStamped       # Home/dock location
+```
+
+## Safety Features
+
+- **E-Stop** (#459): Highest priority, halts operation immediately
+- **Battery protection**: Returns home if <20%
+- **Geofence** (#441): Keeps patrol within 5m boundary
+- **Obstacle avoidance**: LIDAR monitoring
+
+## Integration with Features
+
+- **Patrol** (#446): Waypoint routes
+- **Curiosity** (#470): Exploration during patrol
+- **Person Following**: Approach detected persons
+- **E-Stop** (#459): Emergency override
+- **Geofence** (#441): Boundary constraint
+
+## Launch
+
+```bash
+ros2 launch saltybot_bringup autonomous_mode.launch.py
+```
+
+## Files
+
+- `autonomous_coordinator.xml`: BehaviorTree definition
+- `launch/autonomous_mode.launch.py`: Full launch setup
+- `saltybot_bringup/bt_nodes.py`: Custom BT node plugins
+- `BEHAVIOR_TREE_README.md`: Documentation

jetson/ros2_ws/src/saltybot_bringup/behavior_trees/autonomous_coordinator.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0"?>
+<root BTCPP_format="4">
+  <BehaviorTree ID="AutonomousCoordinator">
+    <ReactiveFallback name="RootFallback">
+      <Inverter><CheckEmergencyStop/></Inverter>
+      <Sequence name="AutonomousSequence">
+        <SetBlackboardVariable var_name="current_mode" var_value="idle"/>
+        <Sequence name="IdleState">
+          <StopRobot/>
+          <WaitForActivation timeout_ms="60000"/>
+        </Sequence>
+        <Sequence name="PatrolState">
+          <SetBlackboardVariable var_name="current_mode" var_value="patrol"/>
+          <CheckBatteryLevel threshold="20"/>
+          <PatrolWithCuriosity/>
+        </Sequence>
+        <Sequence name="InvestigateState">
+          <SetBlackboardVariable var_name="current_mode" var_value="investigate"/>
+          <FollowDetectedPerson/>
+        </Sequence>
+        <Sequence name="InteractState">
+          <SetBlackboardVariable var_name="current_mode" var_value="interact"/>
+          <RecognizeAndGreet/>
+          <Wait wait_duration="30"/>
+        </Sequence>
+        <Sequence name="ReturnState">
+          <SetBlackboardVariable var_name="current_mode" var_value="return"/>
+          <NavigateToHome retry_count="3"/>
+          <StopRobot/>
+        </Sequence>
+      </Sequence>
+    </ReactiveFallback>
+  </BehaviorTree>
+</root>

jetson/ros2_ws/src/saltybot_bringup/launch/autonomous_mode.launch.py

@@ -0,0 +1,19 @@
+"""Autonomous Mode Launcher (Issue #482)"""
+from launch import LaunchDescription
+from launch_ros.actions import Node
+from launch_ros.substitutions import FindPackageShare
+from launch.substitutions import PathJoinSubstitution
+
+def generate_launch_description():
+    saltybot_bringup_dir = FindPackageShare("saltybot_bringup")
+    bt_xml_dir = PathJoinSubstitution([saltybot_bringup_dir, "behavior_trees"])
+    return LaunchDescription([
+        Node(package="saltybot_bt_executor", executable="behavior_tree_executor", name="autonomous_coordinator",
+             parameters=[{"bt_xml_filename": PathJoinSubstitution([bt_xml_dir, "autonomous_coordinator.xml"])}]),
+        Node(package="saltybot_battery_monitor", executable="battery_monitor_node", name="battery_monitor"),
+        Node(package="saltybot_perception", executable="person_detector", name="person_detector"),
+        Node(package="saltybot_lidar_avoidance", executable="obstacle_monitor", name="obstacle_monitor"),
+        Node(package="saltybot_follower", executable="person_follower", name="person_follower"),
+        Node(package="saltybot_curiosity", executable="curiosity_explorer", name="curiosity_explorer"),
+        Node(package="saltybot_emergency_stop", executable="emergency_stop_monitor", name="emergency_stop_monitor"),
+    ])

jetson/ros2_ws/src/saltybot_bringup/saltybot_bringup/bt_nodes.py

@@ -0,0 +1,63 @@
+"""Custom Behavior Tree Node Plugins (Issue #482)"""
+import rclpy
+from rclpy.node import Node
+from py_trees import behaviour, common
+from geometry_msgs.msg import Twist
+from sensor_msgs.msg import BatteryState
+from std_msgs.msg import Float32, Bool
+
+class GetBatteryLevel(behaviour.Behaviour):
+    def __init__(self, name, node: Node):
+        super().__init__(name)
+        self.node = node
+        self.battery_level = 100.0
+        self.subscription = node.create_subscription(BatteryState, '/battery_state', self._battery_callback, 10)
+    def _battery_callback(self, msg):
+        self.battery_level = msg.percentage * 100.0
+    def update(self) -> common.Status:
+        self.blackboard.set('battery_level', self.battery_level, overwrite=True)
+        return common.Status.SUCCESS
+
+class CheckBatteryLevel(behaviour.Behaviour):
+    def __init__(self, name, node: Node, threshold: float = 50.0):
+        super().__init__(name)
+        self.node = node
+        self.threshold = threshold
+        self.battery_level = 100.0
+        self.subscription = node.create_subscription(BatteryState, '/battery_state', self._battery_callback, 10)
+    def _battery_callback(self, msg):
+        self.battery_level = msg.percentage * 100.0
+    def update(self) -> common.Status:
+        return common.Status.SUCCESS if self.battery_level >= self.threshold else common.Status.FAILURE
+
+class CheckPersonDetected(behaviour.Behaviour):
+    def __init__(self, name, node: Node):
+        super().__init__(name)
+        self.node = node
+        self.person_detected = False
+        self.subscription = node.create_subscription(Bool, '/person_detection/detected', self._detection_callback, 10)
+    def _detection_callback(self, msg):
+        self.person_detected = msg.data
+    def update(self) -> common.Status:
+        self.blackboard.set('person_detected', self.person_detected, overwrite=True)
+        return common.Status.SUCCESS if self.person_detected else common.Status.FAILURE
+
+class StopRobot(behaviour.Behaviour):
+    def __init__(self, name, node: Node):
+        super().__init__(name)
+        self.node = node
+        self.cmd_vel_pub = node.create_publisher(Twist, '/cmd_vel', 10)
+    def update(self) -> common.Status:
+        msg = Twist()
+        self.cmd_vel_pub.publish(msg)
+        return common.Status.SUCCESS
+
+class SetBlackboardVariable(behaviour.Behaviour):
+    def __init__(self, name, node: Node, var_name: str, var_value):
+        super().__init__(name)
+        self.node = node
+        self.var_name = var_name
+        self.var_value = var_value
+    def update(self) -> common.Status:
+        self.blackboard.set(self.var_name, self.var_value, overwrite=True)
+        return common.Status.SUCCESS