Auto: ablegacy-8 — per-tag deadband / change filter

Closes #251

docs/drivers/AbLegacy-Test-Fixture.md

@@ -49,6 +49,12 @@ supplies a `FakeAbLegacyTag`.
 - `AbLegacyHostAndStatusTests` — probe + host-status transitions driven by
   fake-returned statuses
 - `AbLegacyDriverTests` — `IDriver` lifecycle
+- `AbLegacyDeadbandTests` — PR 8 per-tag deadband / change filter:
+  absolute-only suppression sequence `[10.0, 10.5, 11.5, 11.6] -> [10.0, 11.5]`,
+  percent-only suppression with a zero-prev short-circuit, both-set logical-OR
+  semantics (Kepware), Boolean edge-only publish, string change-only publish,
+  status-change always-publish, first-seen always-publish, ReinitializeAsync
+  cache wipe, JSON DTO round-trip.
 
 Capability surfaces whose contract is verified: `IDriver`, `IReadable`,
 `IWritable`, `ITagDiscovery`, `ISubscribable`, `IHostConnectivityProbe`,