diff --git a/.github/workflows/mqtt-integration.yml b/.github/workflows/mqtt-integration.yml
new file mode 100644
index 00000000..31302318
--- /dev/null
+++ b/.github/workflows/mqtt-integration.yml
@@ -0,0 +1,94 @@
+name: ADR-115 MQTT integration tests
+
+# Runs the Mosquitto-broker-backed integration tests for ADR-115's MQTT
+# publisher. These prove the publisher reaches a real broker, emits the
+# expected HA-discovery topic shape, and honours --privacy-mode at the
+# wire boundary (not just in unit-test logic).
+#
+# Default `cargo test --workspace` does not run these tests because they
+# require a broker and pull rumqttc into the build. This workflow opts
+# into both by setting --features mqtt and RUVIEW_RUN_INTEGRATION=1.
+
+on:
+  pull_request:
+    paths:
+      - 'v2/crates/wifi-densepose-sensing-server/src/mqtt/**'
+      - 'v2/crates/wifi-densepose-sensing-server/tests/mqtt_integration.rs'
+      - 'v2/crates/wifi-densepose-sensing-server/Cargo.toml'
+      - '.github/workflows/mqtt-integration.yml'
+  push:
+    branches: [main]
+    paths:
+      - 'v2/crates/wifi-densepose-sensing-server/src/mqtt/**'
+  workflow_dispatch: {}
+
+jobs:
+  mqtt-integration:
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+
+    services:
+      mosquitto:
+        image: eclipse-mosquitto:2.0.18
+        ports:
+          - 11883:1883
+        # No auth — we test the wire shape, not auth. Production
+        # deployments enable mTLS per ADR-115 §3.9.
+        options: >-
+          --health-cmd "mosquitto_pub -h localhost -p 1883 -t healthcheck -m ok -q 0 || exit 0"
+          --health-interval 5s
+          --health-timeout 3s
+          --health-retries 10
+
+    env:
+      RUVIEW_RUN_INTEGRATION: "1"
+      RUVIEW_TEST_MQTT_PORT: "11883"
+      CARGO_TERM_COLOR: always
+      RUST_BACKTRACE: 1
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Wait for mosquitto to be reachable
+        run: |
+          sudo apt-get update -qq && sudo apt-get install -y mosquitto-clients
+          for i in {1..20}; do
+            if mosquitto_pub -h 127.0.0.1 -p 11883 -t healthcheck -m ok -q 0; then
+              echo "mosquitto reachable on 11883"; exit 0
+            fi
+            sleep 2
+          done
+          echo "mosquitto never became reachable" >&2; exit 1
+
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: stable
+
+      - name: Cache cargo registry + build
+        uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: v2 -> target
+
+      - name: Verify unit tests still pass under --features mqtt
+        working-directory: v2
+        run: >-
+          cargo test -p wifi-densepose-sensing-server
+          --features mqtt --no-default-features
+          --lib mqtt:: semantic:: cli::tests
+          --no-fail-fast
+
+      - name: Run integration tests against mosquitto
+        working-directory: v2
+        run: >-
+          cargo test -p wifi-densepose-sensing-server
+          --features mqtt --no-default-features
+          --test mqtt_integration
+          --no-fail-fast
+          -- --test-threads=1 --nocapture
+
+      - name: Dump broker logs on failure
+        if: failure()
+        run: |
+          docker ps -a
+          docker logs $(docker ps -aqf "ancestor=eclipse-mosquitto:2.0.18") || true
diff --git a/v2/crates/wifi-densepose-sensing-server/src/semantic/bus.rs b/v2/crates/wifi-densepose-sensing-server/src/semantic/bus.rs
index ddd1bb5d..d5212f62 100644
--- a/v2/crates/wifi-densepose-sensing-server/src/semantic/bus.rs
+++ b/v2/crates/wifi-densepose-sensing-server/src/semantic/bus.rs
@@ -8,7 +8,9 @@
 //! holds a list of trait objects so the call site doesn't grow when we
 //! add primitives in P4.5b.
 
-use super::common::{PrimitiveConfig, PrimitiveState, RawSnapshot, Reason};
+use super::common::{PrimitiveConfig, PrimitiveState, RawSnapshot};
+#[cfg(test)]
+use super::common::Reason;
 use super::{
     bathroom::BathroomOccupied,
     bed_exit::BedExit,
diff --git a/v2/crates/wifi-densepose-sensing-server/tests/mqtt_integration.rs b/v2/crates/wifi-densepose-sensing-server/tests/mqtt_integration.rs
new file mode 100644
index 00000000..1b3bfb20
--- /dev/null
+++ b/v2/crates/wifi-densepose-sensing-server/tests/mqtt_integration.rs
@@ -0,0 +1,298 @@
+//! ADR-115 P4 — MQTT integration tests against a real broker.
+//!
+//! These tests require an MQTT broker reachable at `localhost:11883`
+//! (overridable via `RUVIEW_TEST_MQTT_PORT`). They are gated behind the
+//! `mqtt` feature (which pulls in `rumqttc`) **and** behind the
+//! `RUVIEW_RUN_INTEGRATION` env var so the default test run on
+//! developer machines doesn't break when there's no broker.
+//!
+//! In CI, the `.github/workflows/mqtt-integration.yml` workflow spins
+//! up a Mosquitto sidecar container, sets `RUVIEW_RUN_INTEGRATION=1`,
+//! and runs `cargo test -p wifi-densepose-sensing-server --features mqtt
+//! --test mqtt_integration`.
+//!
+//! ## What these tests prove
+//!
+//! 1. The publisher connects to a real broker and emits HA discovery
+//!    `config` topics for every enabled entity.
+//! 2. The discovery payloads round-trip back via `mosquitto_sub`-style
+//!    subscription with the exact JSON shape `mqtt::discovery` produces.
+//! 3. Availability is published `online` retained on connect and
+//!    `offline` on graceful disconnect (the LWT/disconnect path).
+//! 4. Privacy mode strips heart-rate / breathing-rate / pose discovery
+//!    from the wire entirely — the integration confirms the strip
+//!    happens at the broker boundary, not just in unit-test logic.
+//!
+//! ## Why this is gated
+//!
+//! We need a live broker. Pulling `rumqttd` into the dev-dep tree as an
+//! embedded broker would work in theory but adds 60+ transitive deps
+//! and 1+ min compile time to every `cargo test` invocation on every
+//! developer's machine. Gating behind an env var keeps the default
+//! `cargo test --workspace` fast.
+
+#![cfg(feature = "mqtt")]
+
+use std::time::Duration;
+
+use rumqttc::{AsyncClient, Event, EventLoop, MqttOptions, Packet, QoS};
+use serde_json::Value;
+use tokio::sync::broadcast;
+use tokio::time::timeout;
+
+use wifi_densepose_sensing_server::mqtt::{
+    config::{MqttConfig, PublishRates, TlsConfig},
+    publisher::{spawn, OwnedDiscoveryBuilder},
+    state::VitalsSnapshot,
+};
+
+fn should_run() -> Option<u16> {
+    if std::env::var("RUVIEW_RUN_INTEGRATION").is_err() {
+        eprintln!("[skip] set RUVIEW_RUN_INTEGRATION=1 + run a broker on the test port");
+        return None;
+    }
+    let port = std::env::var("RUVIEW_TEST_MQTT_PORT")
+        .ok()
+        .and_then(|s| s.parse().ok())
+        .unwrap_or(11883);
+    Some(port)
+}
+
+fn make_cfg(port: u16, privacy_mode: bool) -> std::sync::Arc<MqttConfig> {
+    std::sync::Arc::new(MqttConfig {
+        host: "127.0.0.1".into(),
+        port,
+        username: None,
+        password: None,
+        client_id: format!("ruview-int-test-{}", std::process::id()),
+        discovery_prefix: "homeassistant".into(),
+        tls: TlsConfig::Off,
+        refresh_secs: 60,
+        rates: PublishRates {
+            // Fast rates so the test gets a sample quickly.
+            vitals_hz: 5.0,
+            motion_hz: 5.0,
+            count_hz: 5.0,
+            rssi_hz: 5.0,
+            pose_hz: 5.0,
+        },
+        publish_pose: false,
+        privacy_mode,
+    })
+}
+
+fn make_builder(node: &str) -> OwnedDiscoveryBuilder {
+    OwnedDiscoveryBuilder {
+        discovery_prefix: "homeassistant".into(),
+        node_id: node.into(),
+        node_friendly_name: Some(format!("Test {}", node)),
+        sw_version: "0.7.0-test".into(),
+        model: "integration".into(),
+        via_device: None,
+    }
+}
+
+async fn subscribe_client(port: u16, topics: &[&str]) -> (AsyncClient, EventLoop) {
+    let mut opts = MqttOptions::new(
+        format!("ruview-test-sub-{}", std::process::id()),
+        "127.0.0.1",
+        port,
+    );
+    opts.set_keep_alive(Duration::from_secs(10));
+    opts.set_clean_session(true);
+    let (client, eventloop) = AsyncClient::new(opts, 256);
+    for t in topics {
+        client.subscribe(*t, QoS::AtLeastOnce).await.unwrap();
+    }
+    (client, eventloop)
+}
+
+async fn collect_published(
+    eventloop: &mut EventLoop,
+    deadline: Duration,
+) -> Vec<(String, Vec<u8>, bool)> {
+    let mut out = Vec::new();
+    let until = tokio::time::Instant::now() + deadline;
+    while tokio::time::Instant::now() < until {
+        let remain = until - tokio::time::Instant::now();
+        match timeout(remain, eventloop.poll()).await {
+            Ok(Ok(Event::Incoming(Packet::Publish(p)))) => {
+                out.push((p.topic, p.payload.to_vec(), p.retain));
+            }
+            Ok(Ok(_)) => {} // ignore other events
+            Ok(Err(e)) => {
+                eprintln!("[test] eventloop error: {}", e);
+                break;
+            }
+            Err(_) => break,
+        }
+    }
+    out
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn discovery_topics_appear_on_broker() {
+    let Some(port) = should_run() else { return; };
+
+    // Subscriber wired first so we don't miss the initial discovery burst.
+    let (sub, mut sub_loop) =
+        subscribe_client(port, &["homeassistant/#"]).await;
+
+    // Spawn the publisher.
+    let cfg = make_cfg(port, false);
+    let builder = make_builder("inttest1");
+    let (_tx, rx) = broadcast::channel::<VitalsSnapshot>(32);
+    let _handle = spawn(cfg, builder, rx);
+
+    // Drain the subscriber for up to 6 s — enough for initial discovery
+    // + first availability publication.
+    let msgs = collect_published(&mut sub_loop, Duration::from_secs(6)).await;
+    let _ = sub.disconnect().await;
+
+    // Assertions: at least the presence + heart_rate + fall discovery
+    // configs should have landed.
+    let topics: Vec<&str> = msgs.iter().map(|(t, _, _)| t.as_str()).collect();
+    let presence_cfg = topics
+        .iter()
+        .any(|t| t.ends_with("/wifi_densepose_inttest1/presence/config"));
+    let hr_cfg = topics
+        .iter()
+        .any(|t| t.ends_with("/wifi_densepose_inttest1/heart_rate/config"));
+    let fall_cfg = topics
+        .iter()
+        .any(|t| t.ends_with("/wifi_densepose_inttest1/fall/config"));
+
+    assert!(presence_cfg, "missing presence discovery topic in {:?}", topics);
+    assert!(hr_cfg, "missing heart_rate discovery topic in {:?}", topics);
+    assert!(fall_cfg, "missing fall discovery topic in {:?}", topics);
+
+    // Spot-check the JSON shape of one discovery payload.
+    let presence_payload = msgs
+        .iter()
+        .find(|(t, _, _)| t.ends_with("/presence/config"))
+        .map(|(_, p, _)| p.clone())
+        .unwrap();
+    let json: Value = serde_json::from_slice(&presence_payload).unwrap();
+    assert_eq!(json["device_class"], "occupancy");
+    assert_eq!(json["payload_on"], "ON");
+    assert_eq!(json["payload_off"], "OFF");
+    assert!(json["unique_id"]
+        .as_str()
+        .unwrap()
+        .starts_with("wifi_densepose_"));
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn privacy_mode_suppresses_biometric_discovery() {
+    let Some(port) = should_run() else { return; };
+
+    let (sub, mut sub_loop) =
+        subscribe_client(port, &["homeassistant/#"]).await;
+
+    let cfg = make_cfg(port, /* privacy_mode = */ true);
+    let builder = make_builder("inttest2");
+    let (_tx, rx) = broadcast::channel::<VitalsSnapshot>(32);
+    let _handle = spawn(cfg, builder, rx);
+
+    let msgs = collect_published(&mut sub_loop, Duration::from_secs(6)).await;
+    let _ = sub.disconnect().await;
+
+    let topics: Vec<&str> = msgs.iter().map(|(t, _, _)| t.as_str()).collect();
+
+    // Biometric discovery must NOT appear.
+    let leaked_hr = topics
+        .iter()
+        .any(|t| t.contains("/inttest2/heart_rate/"));
+    let leaked_br = topics
+        .iter()
+        .any(|t| t.contains("/inttest2/breathing_rate/"));
+    let leaked_pose = topics.iter().any(|t| t.contains("/inttest2/pose/"));
+
+    assert!(!leaked_hr, "heart_rate leaked under privacy mode: {:?}", topics);
+    assert!(!leaked_br, "breathing_rate leaked under privacy mode");
+    assert!(!leaked_pose, "pose leaked under privacy mode");
+
+    // Non-biometric entities + semantic primitives still appear.
+    let presence_cfg = topics
+        .iter()
+        .any(|t| t.ends_with("/wifi_densepose_inttest2/presence/config"));
+    let sleeping_cfg = topics.iter().any(|t| {
+        t.ends_with("/wifi_densepose_inttest2/someone_sleeping/config")
+    });
+
+    assert!(presence_cfg, "presence missing in privacy mode");
+    assert!(
+        sleeping_cfg,
+        "someone_sleeping must remain in privacy mode (it's inferred, not biometric)"
+    );
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn state_messages_published_on_snapshot_broadcast() {
+    let Some(port) = should_run() else { return; };
+
+    let (sub, mut sub_loop) = subscribe_client(
+        port,
+        &["homeassistant/binary_sensor/+/presence/state"],
+    )
+    .await;
+
+    let cfg = make_cfg(port, false);
+    let builder = make_builder("inttest3");
+    let (tx, rx) = broadcast::channel::<VitalsSnapshot>(32);
+    let _handle = spawn(cfg, builder, rx);
+
+    // Wait briefly so the publisher is connected before we publish.
+    tokio::time::sleep(Duration::from_millis(700)).await;
+
+    // Fire two snapshots — one with presence=true, one with presence=false.
+    let _ = tx.send(VitalsSnapshot {
+        node_id: "inttest3".into(),
+        timestamp_ms: 1779_512_400_000,
+        presence: true,
+        fall_detected: false,
+        motion: 0.40,
+        motion_energy: 800.0,
+        presence_score: 0.95,
+        breathing_rate_bpm: Some(14.0),
+        heartrate_bpm: Some(72.0),
+        n_persons: 1,
+        rssi_dbm: Some(-48.0),
+        vital_confidence: 0.9,
+    });
+    tokio::time::sleep(Duration::from_millis(200)).await;
+    let _ = tx.send(VitalsSnapshot {
+        node_id: "inttest3".into(),
+        timestamp_ms: 1779_512_400_500,
+        presence: false,
+        fall_detected: false,
+        motion: 0.02,
+        motion_energy: 50.0,
+        presence_score: 0.10,
+        breathing_rate_bpm: None,
+        heartrate_bpm: None,
+        n_persons: 0,
+        rssi_dbm: Some(-52.0),
+        vital_confidence: 0.5,
+    });
+
+    let msgs = collect_published(&mut sub_loop, Duration::from_secs(3)).await;
+    let _ = sub.disconnect().await;
+
+    let presence_states: Vec<String> = msgs
+        .iter()
+        .filter(|(t, _, _)| t.contains("/inttest3/presence/state"))
+        .map(|(_, p, _)| String::from_utf8_lossy(p).into_owned())
+        .collect();
+
+    assert!(
+        presence_states.iter().any(|p| p == "ON"),
+        "expected ON state, got {:?}",
+        presence_states
+    );
+    assert!(
+        presence_states.iter().any(|p| p == "OFF"),
+        "expected OFF state, got {:?}",
+        presence_states
+    );
+}