docs(phase4c): cross-driver 1-D array support + isArray/arrayLength keys + coverage matrix

docs/drivers/TwinCAT.md

@@ -121,6 +121,31 @@ writes use the driver-wide `Timeout`.
 - **CLI** — [Driver.TwinCAT.Cli.md](../Driver.TwinCAT.Cli.md) documents the
   standalone read/write/browse/probe CLI for manual checks.
 
+## 1-D array support
+
+A TwinCAT tag becomes a **1-D OPC UA array node** when its `TagConfig` JSON carries
+`"isArray": true` and `"arrayLength": N` (N ≥ 1).  The canonical rule:
+`isArray: true` + `arrayLength >= 1` → array; `isArray: false` (any length) → scalar.
+
+**Read mechanism** — the driver performs an **ADS native array symbol read** against the
+declared `SymbolPath`.  ADS returns the full array value buffer for a symbol that maps to a
+TwinCAT array type (e.g. `ARRAY [0..9] OF REAL`); the driver reads `N` elements from the
+response.  When `UseNativeNotifications` is enabled, ADS also pushes array-value changes in
+a single notification payload — no per-element polling.
+
+**Unit test coverage** — `tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/` covers
+the array symbol read path via the fake ADS client factory.  The TwinCAT integration
+fixture is down during normal dev.
+
+**Live-verify** — integration-fixture-gated (requires the TwinCAT Docker fixture / AMS router).
+
+**Deferrals** — array *writes* (`ADS WriteValueAsync` for an array), multi-dimensional
+arrays, per-element historization.  `IRediscoverable` still fires and rebuilds array nodes
+on PLC re-download (unchanged semantics from scalar nodes).
+
+See [Uns.md §Array tags](../Uns.md#array-tags-1-d) for the cross-driver coverage matrix
+and the UI authoring flow.
+
 ## Further reading
 
 - [`docs/v2/driver-specs.md §6`](../v2/driver-specs.md) — full per-field spec and