t37 made MAC-less zeroconf discovery honour Home Assistant's own `_async_handle_discovery_without_unique_id` contract — the helper is a coroutine and its dedup (abort `already_configured` when ANY entry exists for this domain, abort `already_in_progress` when another flow runs) only happens when it is awaited. That is stricter than the accidental host-equality guard it replaced, so it changes what a user can expect: * with a MAC, discovery still aborts duplicates and updates a moved device's hosts; * without a MAC, a second (or third) Shield must be added MANUALLY — discovery will abort as "already configured". Someone with two Shields would otherwise read that abort as a bug. The README now has a "Discovery (zeroconf)" section under Configuration stating the rule and the manual route, and the drift sweep's docstring carries the same note next to the D3 entry, so the decision is discoverable from wherever you meet it. Verified: 289 passed, 2 skipped; ruff clean.