The mqtt-integration test suite still failed `state_messages_published_
on_snapshot_broadcast` after the timing fix (5ed8e3451) — but with a
new symptom: 'expected ON state, got []'. The subscriber captured ZERO
messages on the presence state topic.
Root cause: all three integration tests built `client_id` as
`ruview-int-test-<pid>` — the same string for every test in the
sequential cargo-test run. MQTT brokers default to "session takeover":
when a new connect arrives with the same client_id as an existing
session, mosquitto disconnects the old one immediately.
Sequence on CI (`--test-threads=1`):
1. discovery_topics_appear_on_broker connects (ruview-int-test-1234)
2. test passes; publisher task continues running in background
3. privacy_mode_suppresses_biometric_discovery connects (same id)
→ mosquitto kicks test 1's publisher mid-rumqttc-disconnect-handshake
4. state_messages_published_on_snapshot_broadcast connects (same id)
→ mosquitto kicks test 2's publisher
→ test 3's publisher in turn races with the broker's cleanup
and its first publishes may land in a half-cleaned session
→ state messages dropped silently
Fix: include a per-test label in the client_id
(`ruview-int-test-<pid>-<label>` — labels: "discovery", "privacy",
"state"). Each test gets its own MQTT session; no cross-test takeover.
Refs PR #778, issue #776.
Co-Authored-By: claude-flow <ruv@ruv.net>
2aeed32a72