diff --git a/jetson/ros2_ws/src/saltybot_social/config/mesh_params.yaml b/jetson/ros2_ws/src/saltybot_social/config/mesh_params.yaml
new file mode 100644
index 0000000..b6549de
--- /dev/null
+++ b/jetson/ros2_ws/src/saltybot_social/config/mesh_params.yaml
@@ -0,0 +1,8 @@
+mesh_comms_node:
+  ros__parameters:
+    robot_id: "saltybot_1"           # Set to $ROBOT_ID; override per-robot
+    namespace: ""                    # "" = default namespace; e.g. "/saltybot_1"
+    announce_rate_hz: 1.0            # Heartbeat rate (Hz) — keep <= 2 Hz on mesh
+    peer_timeout_s: 5.0              # Drop peer after this many seconds without announce
+    handoff_distance_m: 3.0          # (guard) min distance for handoff trigger (m)
+    greeted_memory_s: 300.0          # Forget a greeted name after N seconds
diff --git a/jetson/ros2_ws/src/saltybot_social/launch/mesh.launch.py b/jetson/ros2_ws/src/saltybot_social/launch/mesh.launch.py
new file mode 100644
index 0000000..0bc357d
--- /dev/null
+++ b/jetson/ros2_ws/src/saltybot_social/launch/mesh.launch.py
@@ -0,0 +1,51 @@
+"""mesh.launch.py — Launch the social mesh comms node (Issue #171).
+
+Usage:
+  ros2 launch saltybot_social mesh.launch.py
+  ros2 launch saltybot_social mesh.launch.py robot_id:=saltybot_2
+"""
+
+import os
+from ament_index_python.packages import get_package_share_directory
+from launch import LaunchDescription
+from launch.actions import DeclareLaunchArgument
+from launch.substitutions import LaunchConfiguration
+from launch_ros.actions import Node
+
+
+def generate_launch_description():
+    pkg = get_package_share_directory("saltybot_social")
+    cfg = os.path.join(pkg, "config", "mesh_params.yaml")
+
+    return LaunchDescription([
+        DeclareLaunchArgument(
+            "robot_id",
+            default_value=os.environ.get("ROBOT_ID", "saltybot_1"),
+            description="Unique robot identifier for mesh announcements",
+        ),
+        DeclareLaunchArgument(
+            "announce_rate_hz",
+            default_value="1.0",
+            description="Heartbeat rate (Hz)",
+        ),
+        DeclareLaunchArgument(
+            "peer_timeout_s",
+            default_value="5.0",
+            description="Seconds before a peer is considered lost",
+        ),
+
+        Node(
+            package="saltybot_social",
+            executable="mesh_comms_node",
+            name="mesh_comms_node",
+            output="screen",
+            parameters=[
+                cfg,
+                {
+                    "robot_id":          LaunchConfiguration("robot_id"),
+                    "announce_rate_hz":  LaunchConfiguration("announce_rate_hz"),
+                    "peer_timeout_s":    LaunchConfiguration("peer_timeout_s"),
+                },
+            ],
+        ),
+    ])
diff --git a/jetson/ros2_ws/src/saltybot_social/saltybot_social/mesh_comms_node.py b/jetson/ros2_ws/src/saltybot_social/saltybot_social/mesh_comms_node.py
new file mode 100644
index 0000000..02b9618
--- /dev/null
+++ b/jetson/ros2_ws/src/saltybot_social/saltybot_social/mesh_comms_node.py
@@ -0,0 +1,237 @@
+"""mesh_comms_node.py — Robot-to-robot social mesh communication.
+Issue #171
+
+Topics:
+  Publish:   /social/mesh/announce   (MeshPeer, 1 Hz)  — presence heartbeat
+             /social/mesh/handoff    (MeshHandoff)     — person context on LEAVING
+             /social/mesh/peers      (String / JSON)   — peer list for UI
+             /social/mesh/greeted    (String / JSON)   — mesh-wide greeted names
+  Subscribe: /social/mesh/announce   (MeshPeer)        — remote peer announcements
+             /social/mesh/handoff    (MeshHandoff)     — incoming handoffs
+             /social/person_states   (PersonStateArray)
+             /social/orchestrator/state (String / JSON)
+
+Parameters:
+  robot_id          (str, $ROBOT_ID or "saltybot_1") — unique robot identifier
+  namespace         (str, $ROS_NAMESPACE or "")      — ROS2 namespace
+  announce_rate_hz  (float, 1.0)   — heartbeat rate
+  peer_timeout_s    (float, 5.0)   — drop peer after N seconds without announce
+  handoff_distance_m (float, 3.0)  — max distance to trigger handoff (unused guard)
+  greeted_memory_s  (float, 300.0) — forget a greeted name after N seconds
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import threading
+import time
+from typing import Dict, Set
+
+import rclpy
+from rclpy.node import Node
+from rclpy.qos import QoSProfile, ReliabilityPolicy, DurabilityPolicy
+from std_msgs.msg import String
+
+from saltybot_social_msgs.msg import PersonStateArray, MeshPeer, MeshHandoff
+
+_LEAVING  = 4  # PersonState.STATE_LEAVING
+_ENGAGED  = 2  # PersonState.STATE_ENGAGED
+_TALKING  = 3  # PersonState.STATE_TALKING
+
+
+class MeshCommsNode(Node):
+    """Robot mesh comms — peer announce, person handoff, greeting deduplication."""
+
+    def __init__(self) -> None:
+        super().__init__("mesh_comms_node")
+
+        self.declare_parameter("robot_id", os.environ.get("ROBOT_ID", "saltybot_1"))
+        self.declare_parameter("namespace", os.environ.get("ROS_NAMESPACE", ""))
+        self.declare_parameter("announce_rate_hz", 1.0)
+        self.declare_parameter("peer_timeout_s", 5.0)
+        self.declare_parameter("handoff_distance_m", 3.0)
+        self.declare_parameter("greeted_memory_s", 300.0)
+
+        self._robot_id     = self.get_parameter("robot_id").value
+        self._ns           = self.get_parameter("namespace").value
+        self._peer_timeout = self.get_parameter("peer_timeout_s").value
+        self._handoff_dist = self.get_parameter("handoff_distance_m").value
+        self._greeted_mem  = self.get_parameter("greeted_memory_s").value
+
+        qos = QoSProfile(depth=10)
+        mesh_qos = QoSProfile(
+            depth=10,
+            reliability=ReliabilityPolicy.BEST_EFFORT,
+            durability=DurabilityPolicy.VOLATILE,
+        )
+
+        self._announce_pub = self.create_publisher(MeshPeer,    "/social/mesh/announce", mesh_qos)
+        self._handoff_pub  = self.create_publisher(MeshHandoff, "/social/mesh/handoff",  qos)
+        self._peers_pub    = self.create_publisher(String,      "/social/mesh/peers",    qos)
+        self._greeted_pub  = self.create_publisher(String,      "/social/mesh/greeted",  qos)
+
+        self._announce_sub = self.create_subscription(
+            MeshPeer, "/social/mesh/announce", self._on_announce, mesh_qos)
+        self._handoff_sub  = self.create_subscription(
+            MeshHandoff, "/social/mesh/handoff", self._on_handoff, qos)
+        self._persons_sub  = self.create_subscription(
+            PersonStateArray, "/social/person_states", self._on_person_states, qos)
+        self._orch_sub     = self.create_subscription(
+            String, "/social/orchestrator/state", self._on_orch_state, qos)
+
+        self._lock                         = threading.Lock()
+        self._peers: Dict[str, dict]       = {}   # robot_id → {last_seen, msg}
+        self._person_states: dict          = {}   # person_id → PersonState
+        self._social_state                 = "idle"
+        self._greeted: Dict[str, float]    = {}   # person_name → timestamp
+        self._handoff_sent: Set[str]       = set()  # str(person_id) already handed off
+
+        rate = self.get_parameter("announce_rate_hz").value
+        self._announce_timer = self.create_timer(1.0 / rate, self._publish_announce)
+        self._cleanup_timer  = self.create_timer(2.0, self._cleanup)
+
+        self.get_logger().info(
+            f"MeshCommsNode ready (robot_id={self._robot_id}, "
+            f"peer_timeout={self._peer_timeout}s, handoff_dist={self._handoff_dist}m)"
+        )
+
+    # ── Subscriber callbacks ──────────────────────────────────────────────────
+
+    def _on_orch_state(self, msg: String) -> None:
+        try:
+            d = json.loads(msg.data)
+            with self._lock:
+                self._social_state = d.get("state", "idle")
+        except Exception:
+            pass
+
+    def _on_person_states(self, msg: PersonStateArray) -> None:
+        with self._lock:
+            new_states = {p.person_id: p for p in msg.persons}
+            for pid, ps in new_states.items():
+                prev = self._person_states.get(pid)
+                if (prev is not None
+                        and prev.state != _LEAVING
+                        and ps.state == _LEAVING
+                        and str(pid) not in self._handoff_sent):
+                    self._trigger_handoff(ps)
+            self._person_states = new_states
+
+    def _on_announce(self, msg: MeshPeer) -> None:
+        if msg.robot_id == self._robot_id:
+            return
+        with self._lock:
+            self._peers[msg.robot_id] = {"last_seen": time.time(), "msg": msg}
+            for name in msg.greeted_person_names:
+                if name and name not in self._greeted:
+                    self._greeted[name] = time.time()
+        self._publish_greeted()
+
+    def _on_handoff(self, msg: MeshHandoff) -> None:
+        if msg.from_robot_id == self._robot_id:
+            return
+        self.get_logger().info(
+            f"Handoff received from [{msg.from_robot_id}]: "
+            f"person='{msg.person_name or msg.person_id}' "
+            f"lang={msg.language or '?'} "
+            f"bearing={msg.bearing_to_target_deg:.0f}° dist={msg.distance_m:.1f}m"
+        )
+
+    # ── Publish helpers ───────────────────────────────────────────────────────
+
+    def _trigger_handoff(self, ps) -> None:
+        """Build and publish a MeshHandoff for a LEAVING person. Must hold self._lock."""
+        msg = MeshHandoff()
+        msg.header.stamp = self.get_clock().now().to_msg()
+        msg.from_robot_id             = self._robot_id
+        msg.to_robot_id               = ""
+        msg.person_id                 = str(ps.person_id)
+        msg.person_name               = ps.person_name
+        msg.face_id                   = ps.face_id
+        msg.speaker_id                = ps.speaker_id
+        msg.bearing_to_target_deg     = ps.bearing_deg
+        msg.distance_m                = ps.distance
+        msg.engagement_score          = ps.engagement_score
+        msg.conversation_summary      = ""
+        msg.last_utterance            = ""
+        msg.last_response             = ""
+        msg.language                  = ""
+        self._handoff_sent.add(str(ps.person_id))
+        self._handoff_pub.publish(msg)
+        self.get_logger().info(
+            f"Handoff → '{ps.person_name or ps.person_id}' "
+            f"bearing={ps.bearing_deg:.0f}° dist={ps.distance:.1f}m"
+        )
+
+    def _publish_announce(self) -> None:
+        with self._lock:
+            active_ids = [
+                pid for pid, ps in self._person_states.items()
+                if ps.state in (_ENGAGED, _TALKING)
+            ]
+            greeted_names = [
+                name for name, t in self._greeted.items()
+                if time.time() - t < self._greeted_mem
+            ]
+            state = self._social_state
+        msg = MeshPeer()
+        msg.header.stamp          = self.get_clock().now().to_msg()
+        msg.robot_id              = self._robot_id
+        msg.namespace             = self._ns
+        msg.social_state          = state
+        msg.active_person_ids     = active_ids
+        msg.greeted_person_names  = greeted_names
+        msg.battery_pct           = -1.0
+        self._announce_pub.publish(msg)
+        self._publish_peers_status()
+
+    def _publish_peers_status(self) -> None:
+        with self._lock:
+            entries = [
+                {
+                    "robot_id":       rid,
+                    "social_state":   d["msg"].social_state,
+                    "active_persons": len(d["msg"].active_person_ids),
+                    "age_s":          round(time.time() - d["last_seen"], 1),
+                }
+                for rid, d in self._peers.items()
+            ]
+        msg = String()
+        msg.data = json.dumps({"peers": entries, "ts": time.time()})
+        self._peers_pub.publish(msg)
+
+    def _publish_greeted(self) -> None:
+        with self._lock:
+            names = [n for n, t in self._greeted.items()
+                     if time.time() - t < self._greeted_mem]
+        msg = String()
+        msg.data = json.dumps({"greeted": names, "ts": time.time()})
+        self._greeted_pub.publish(msg)
+
+    # ── Cleanup ───────────────────────────────────────────────────────────────
+
+    def _cleanup(self) -> None:
+        now = time.time()
+        with self._lock:
+            dead = [rid for rid, d in self._peers.items()
+                    if now - d["last_seen"] > self._peer_timeout]
+            for rid in dead:
+                self.get_logger().info(f"Peer lost: {rid}")
+                del self._peers[rid]
+            self._greeted = {n: t for n, t in self._greeted.items()
+                             if now - t < self._greeted_mem}
+            active_pids = {str(p) for p in self._person_states}
+            self._handoff_sent &= active_pids
+
+
+def main(args=None) -> None:
+    rclpy.init(args=args)
+    node = MeshCommsNode()
+    try:
+        rclpy.spin(node)
+    except KeyboardInterrupt:
+        pass
+    finally:
+        node.destroy_node()
+        rclpy.shutdown()
diff --git a/jetson/ros2_ws/src/saltybot_social/setup.py b/jetson/ros2_ws/src/saltybot_social/setup.py
index 860096f..3164e19 100644
--- a/jetson/ros2_ws/src/saltybot_social/setup.py
+++ b/jetson/ros2_ws/src/saltybot_social/setup.py
@@ -39,6 +39,8 @@ setup(
             'gesture_node = saltybot_social.gesture_node:main',
             # Facial expression recognition (Issue #161)
             'emotion_node = saltybot_social.emotion_node:main',
+            # Robot mesh communication (Issue #171)
+            'mesh_comms_node = saltybot_social.mesh_comms_node:main',
         ],
     },
 )
diff --git a/jetson/ros2_ws/src/saltybot_social/test/test_mesh_comms.py b/jetson/ros2_ws/src/saltybot_social/test/test_mesh_comms.py
new file mode 100644
index 0000000..af79f2e
--- /dev/null
+++ b/jetson/ros2_ws/src/saltybot_social/test/test_mesh_comms.py
@@ -0,0 +1,278 @@
+"""test_mesh_comms.py -- Unit tests for Issue #171 robot mesh comms."""
+
+from __future__ import annotations
+import json, os, time
+from typing import Dict
+import pytest
+
+
+def _pkg_root():
+    return os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+
+
+def _read_src(rel_path):
+    with open(os.path.join(_pkg_root(), rel_path)) as f:
+        return f.read()
+
+
+# ── Message definitions ───────────────────────────────────────────────────────
+
+class TestMeshPeerMsg:
+    @pytest.fixture(scope="class")
+    def src(self):
+        return _read_src("../saltybot_social_msgs/msg/MeshPeer.msg")
+
+    def test_robot_id(self, src):      assert "string  robot_id" in src
+    def test_namespace(self, src):     assert "string  namespace" in src
+    def test_social_state(self, src):  assert "string  social_state" in src
+    def test_active_ids(self, src):    assert "int32[] active_person_ids" in src
+    def test_greeted(self, src):       assert "string[] greeted_person_names" in src
+    def test_battery(self, src):       assert "float32 battery_pct" in src
+    def test_header(self, src):        assert "std_msgs/Header" in src
+    def test_issue_tag(self, src):     assert "171" in src
+
+
+class TestMeshHandoffMsg:
+    @pytest.fixture(scope="class")
+    def src(self):
+        return _read_src("../saltybot_social_msgs/msg/MeshHandoff.msg")
+
+    def test_from_robot(self, src):    assert "from_robot_id" in src
+    def test_to_robot(self, src):      assert "to_robot_id" in src
+    def test_person_id(self, src):     assert "string  person_id" in src
+    def test_person_name(self, src):   assert "string  person_name" in src
+    def test_face_id(self, src):       assert "int32   face_id" in src
+    def test_speaker_id(self, src):    assert "string  speaker_id" in src
+    def test_bearing(self, src):       assert "bearing_to_target_deg" in src
+    def test_distance(self, src):      assert "distance_m" in src
+    def test_engagement(self, src):    assert "engagement_score" in src
+    def test_summary(self, src):       assert "conversation_summary" in src
+    def test_last_utterance(self, src):assert "last_utterance" in src
+    def test_last_response(self, src): assert "last_response" in src
+    def test_language(self, src):      assert "string  language" in src
+    def test_header(self, src):        assert "std_msgs/Header" in src
+
+
+# ── CMakeLists includes new msgs ──────────────────────────────────────────────
+
+class TestCMakeLists:
+    @pytest.fixture(scope="class")
+    def src(self):
+        return _read_src("../saltybot_social_msgs/CMakeLists.txt")
+
+    def test_mesh_peer(self, src):    assert '"msg/MeshPeer.msg"' in src
+    def test_mesh_handoff(self, src): assert '"msg/MeshHandoff.msg"' in src
+    def test_issue_tag(self, src):    assert "Issue #171" in src
+
+
+# ── Node source structure ─────────────────────────────────────────────────────
+
+class TestMeshCommsNodeSrc:
+    @pytest.fixture(scope="class")
+    def src(self):
+        return _read_src("saltybot_social/mesh_comms_node.py")
+
+    def test_class_defined(self, src):        assert "class MeshCommsNode" in src
+    def test_robot_id_param(self, src):       assert '"robot_id"' in src
+    def test_announce_rate_param(self, src):  assert '"announce_rate_hz"' in src
+    def test_peer_timeout_param(self, src):   assert '"peer_timeout_s"' in src
+    def test_handoff_dist_param(self, src):   assert '"handoff_distance_m"' in src
+    def test_greeted_memory_param(self, src): assert '"greeted_memory_s"' in src
+    def test_announce_pub(self, src):         assert "/social/mesh/announce" in src
+    def test_handoff_pub(self, src):          assert "/social/mesh/handoff" in src
+    def test_peers_pub(self, src):            assert "/social/mesh/peers" in src
+    def test_greeted_pub(self, src):          assert "/social/mesh/greeted" in src
+    def test_person_states_sub(self, src):    assert "/social/person_states" in src
+    def test_orch_state_sub(self, src):       assert "/social/orchestrator/state" in src
+    def test_on_announce(self, src):          assert "_on_announce" in src
+    def test_on_handoff(self, src):           assert "_on_handoff" in src
+    def test_on_person_states(self, src):     assert "_on_person_states" in src
+    def test_trigger_handoff(self, src):      assert "_trigger_handoff" in src
+    def test_publish_announce(self, src):     assert "_publish_announce" in src
+    def test_cleanup(self, src):              assert "_cleanup" in src
+    def test_leaving_constant(self, src):     assert "_LEAVING" in src
+    def test_engaged_constant(self, src):     assert "_ENGAGED" in src
+    def test_talking_constant(self, src):     assert "_TALKING" in src
+    def test_main(self, src):                 assert "def main" in src
+    def test_no_self_announce(self, src):
+        assert "self._robot_id" in src  # ignores own announcements
+    def test_mesh_qos_best_effort(self, src): assert "BEST_EFFORT" in src
+    def test_issue_tag(self, src):            assert "171" in src
+
+
+# ── setup.py entry point ──────────────────────────────────────────────────────
+
+class TestSetupPy:
+    @pytest.fixture(scope="class")
+    def src(self):
+        return _read_src("setup.py")
+
+    def test_mesh_entry_point(self, src):
+        assert "mesh_comms_node = saltybot_social.mesh_comms_node:main" in src
+
+
+# ── Config file ───────────────────────────────────────────────────────────────
+
+class TestMeshConfig:
+    @pytest.fixture(scope="class")
+    def src(self):
+        return _read_src("config/mesh_params.yaml")
+
+    def test_node_name(self, src):       assert "mesh_comms_node:" in src
+    def test_robot_id(self, src):        assert "robot_id:" in src
+    def test_announce_rate(self, src):   assert "announce_rate_hz:" in src
+    def test_peer_timeout(self, src):    assert "peer_timeout_s:" in src
+    def test_handoff_dist(self, src):    assert "handoff_distance_m:" in src
+    def test_greeted_memory(self, src):  assert "greeted_memory_s:" in src
+
+
+# ── Peer tracking logic (pure Python, no ROS) ────────────────────────────────
+
+class TestPeerTracking:
+    def _make_peers(self):
+        return {}
+
+    def _add_peer(self, peers, rid, state, active, greeted):
+        peers[rid] = {
+            "last_seen": time.time(),
+            "msg": type("M", (), {
+                "social_state": state,
+                "active_person_ids": active,
+                "greeted_person_names": greeted,
+            })(),
+        }
+
+    def _cleanup(self, peers, timeout=5.0):
+        now = time.time()
+        return {rid: d for rid, d in peers.items()
+                if now - d["last_seen"] <= timeout}
+
+    def test_add_peer(self):
+        peers = self._make_peers()
+        self._add_peer(peers, "bot2", "idle", [], [])
+        assert "bot2" in peers
+
+    def test_ignore_self(self):
+        peers = self._make_peers()
+        robot_id = "saltybot_1"
+        incoming_id = "saltybot_1"
+        if incoming_id != robot_id:
+            self._add_peer(peers, incoming_id, "idle", [], [])
+        assert "saltybot_1" not in peers
+
+    def test_peer_replaced_on_update(self):
+        peers = self._make_peers()
+        self._add_peer(peers, "bot2", "idle", [], [])
+        self._add_peer(peers, "bot2", "speaking", [42], [])
+        assert peers["bot2"]["msg"].social_state == "speaking"
+
+    def test_cleanup_removes_stale(self):
+        peers = self._make_peers()
+        peers["bot3"] = {"last_seen": time.time() - 10, "msg": None}
+        self._add_peer(peers, "bot4", "idle", [], [])
+        cleaned = self._cleanup(peers, timeout=5.0)
+        assert "bot3" not in cleaned
+        assert "bot4" in cleaned
+
+    def test_multiple_peers(self):
+        peers = self._make_peers()
+        for i in range(5):
+            self._add_peer(peers, f"bot{i}", "idle", [], [])
+        assert len(peers) == 5
+
+
+# ── Greeting deduplication logic ─────────────────────────────────────────────
+
+class TestGreetingDedup:
+    def test_new_name_added(self):
+        greeted: Dict[str, float] = {}
+        name = "Alice"
+        if name not in greeted:
+            greeted[name] = time.time()
+        assert "Alice" in greeted
+
+    def test_existing_name_not_overwritten(self):
+        greeted = {"Alice": 1000.0}
+        t_before = greeted["Alice"]
+        if "Alice" not in greeted:
+            greeted["Alice"] = time.time()
+        assert greeted["Alice"] == t_before
+
+    def test_peer_names_merged(self):
+        greeted: Dict[str, float] = {}
+        peer_names = ["Alice", "Bob"]
+        for n in peer_names:
+            if n and n not in greeted:
+                greeted[n] = time.time()
+        assert "Alice" in greeted and "Bob" in greeted
+
+    def test_expire_old_names(self):
+        greeted = {"Alice": time.time() - 400, "Bob": time.time()}
+        memory_s = 300.0
+        fresh = {n: t for n, t in greeted.items() if time.time() - t < memory_s}
+        assert "Alice" not in fresh and "Bob" in fresh
+
+
+# ── Handoff trigger logic ─────────────────────────────────────────────────────
+
+class TestHandoffTrigger:
+    def _should_handoff(self, prev_state, new_state, pid, sent):
+        _LEAVING = 4
+        return (prev_state != _LEAVING
+                and new_state == _LEAVING
+                and str(pid) not in sent)
+
+    def test_triggers_on_leaving(self):
+        assert self._should_handoff(2, 4, 1, set())
+
+    def test_no_duplicate_handoff(self):
+        sent = {"1"}
+        assert not self._should_handoff(2, 4, 1, sent)
+
+    def test_no_trigger_if_already_leaving(self):
+        assert not self._should_handoff(4, 4, 1, set())
+
+    def test_triggers_for_different_person(self):
+        sent = {"1"}
+        assert self._should_handoff(2, 4, 2, sent)
+
+    def test_handoff_sent_cleared_when_person_gone(self):
+        sent = {"1", "2", "3"}
+        active_pids = {"2", "3"}
+        sent &= active_pids
+        assert "1" not in sent and "2" in sent
+
+
+# ── JSON status blob ──────────────────────────────────────────────────────────
+
+class TestPeersBlob:
+    def test_peers_json(self):
+        peers = {
+            "bot2": {
+                "last_seen": time.time(),
+                "msg": type("M", (), {
+                    "social_state": "idle",
+                    "active_person_ids": [],
+                })(),
+            }
+        }
+        entries = [
+            {
+                "robot_id":       rid,
+                "social_state":   d["msg"].social_state,
+                "active_persons": len(d["msg"].active_person_ids),
+                "age_s":          round(time.time() - d["last_seen"], 1),
+            }
+            for rid, d in peers.items()
+        ]
+        blob = json.dumps({"peers": entries, "ts": time.time()})
+        parsed = json.loads(blob)
+        assert len(parsed["peers"]) == 1
+        assert parsed["peers"][0]["robot_id"] == "bot2"
+
+    def test_greeted_json(self):
+        greeted = {"Alice": time.time(), "Bob": time.time()}
+        names = list(greeted.keys())
+        blob = json.dumps({"greeted": names, "ts": time.time()})
+        parsed = json.loads(blob)
+        assert "Alice" in parsed["greeted"] and "Bob" in parsed["greeted"]
diff --git a/jetson/ros2_ws/src/saltybot_social_msgs/CMakeLists.txt b/jetson/ros2_ws/src/saltybot_social_msgs/CMakeLists.txt
index 6a27435..86d7053 100644
--- a/jetson/ros2_ws/src/saltybot_social_msgs/CMakeLists.txt
+++ b/jetson/ros2_ws/src/saltybot_social_msgs/CMakeLists.txt
@@ -41,6 +41,9 @@ rosidl_generate_interfaces(${PROJECT_NAME}
   # Issue #161 — emotion detection
   "msg/Expression.msg"
   "msg/ExpressionArray.msg"
+  # Issue #171 — robot mesh comms
+  "msg/MeshPeer.msg"
+  "msg/MeshHandoff.msg"
   DEPENDENCIES std_msgs geometry_msgs builtin_interfaces
 )
 
diff --git a/jetson/ros2_ws/src/saltybot_social_msgs/msg/MeshHandoff.msg b/jetson/ros2_ws/src/saltybot_social_msgs/msg/MeshHandoff.msg
new file mode 100644
index 0000000..ce98423
--- /dev/null
+++ b/jetson/ros2_ws/src/saltybot_social_msgs/msg/MeshHandoff.msg
@@ -0,0 +1,27 @@
+# MeshHandoff.msg — Person context transfer between robots.
+# Published on /social/mesh/handoff when a tracked person transitions to
+# STATE_LEAVING, enabling a nearby robot to warm-start LLM conversation context.
+# Issue #171
+
+std_msgs/Header header
+
+string  from_robot_id           # Robot publishing this handoff
+string  to_robot_id             # Intended recipient robot_id; "" = broadcast
+
+# Person identity
+string  person_id               # e.g. "person_42"
+string  person_name             # "" if unknown
+int32   face_id                 # -1 if unknown
+string  speaker_id              # "" if unknown
+
+# Spatial context at handoff time
+float32 bearing_to_target_deg   # Person's bearing from from_robot (°, +CW from forward)
+float32 distance_m              # Person's distance from from_robot (metres)
+float32 engagement_score        # 0..1
+
+# Conversation warm-start context
+string  conversation_summary    # LLM-generated summary of prior exchanges
+string  last_utterance          # Person's last utterance to from_robot
+string  last_response           # Robot's last response to person
+
+string  language                # BCP-47 code e.g. "en", "fr" (empty = unknown)
diff --git a/jetson/ros2_ws/src/saltybot_social_msgs/msg/MeshPeer.msg b/jetson/ros2_ws/src/saltybot_social_msgs/msg/MeshPeer.msg
new file mode 100644
index 0000000..c03d571
--- /dev/null
+++ b/jetson/ros2_ws/src/saltybot_social_msgs/msg/MeshPeer.msg
@@ -0,0 +1,20 @@
+# MeshPeer.msg — Robot social presence announcement.
+# Published by mesh_comms_node on /social/mesh/announce at 1 Hz.
+# All robots sharing the same DDS domain receive peer announcements via multicast.
+# Issue #171
+
+std_msgs/Header header
+
+string  robot_id                # e.g. "saltybot_1"
+string  namespace               # ROS2 namespace, e.g. "/saltybot_1" (empty = default)
+
+# Current social pipeline state (mirrors orchestrator PipelineState)
+string  social_state            # "idle" | "listening" | "thinking" | "speaking" | "throttled"
+
+# Active person IDs this robot is currently engaged with or talking to
+int32[] active_person_ids
+
+# Names greeted since last boot — used for mesh-wide greeting deduplication
+string[] greeted_person_names
+
+float32 battery_pct             # 0..100; -1 = unknown