Auto: focas-f2d — PMC range coalescing

Closes #266

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/IFocasClient.cs

@@ -184,6 +184,45 @@ public interface IFocasClient : IDisposable
     /// </summary>
     Task SetPathAsync(int pathId, CancellationToken cancellationToken)
         => Task.CompletedTask;
+
+    /// <summary>
+    ///     Read a contiguous range of PMC bytes in a single wire call (FOCAS
+    ///     <c>pmc_rdpmcrng</c> with byte data type) for the given <paramref name="letter"/>
+    ///     (<c>R</c>, <c>D</c>, <c>X</c>, etc.) starting at <paramref name="startByte"/> and
+    ///     spanning <paramref name="byteCount"/> bytes. Returned tuple has the byte buffer
+    ///     (length <paramref name="byteCount"/> on success) + the OPC UA status mapped through
+    ///     <see cref="FocasStatusMapper"/>. Used by <see cref="FocasDriver"/> to coalesce
+    ///     same-letter/same-path PMC reads in a batch into one round trip per range
+    ///     (issue #266 — see <see cref="Wire.FocasPmcCoalescer"/>).
+    ///     <para>
+    ///     Default falls back to per-byte <see cref="ReadAsync(FocasAddress, FocasDataType, CancellationToken)"/>
+    ///     calls so transport variants that haven't extended their wire surface still work
+    ///     correctly — they just won't see the round-trip reduction. The fallback short-circuits
+    ///     on the first non-Good status so a partial buffer isn't returned with a Good code.
+    ///     </para>
+    /// </summary>
+    async Task<(byte[]? buffer, uint status)> ReadPmcRangeAsync(
+        string letter, int pathId, int startByte, int byteCount, CancellationToken cancellationToken)
+    {
+        if (byteCount <= 0) return (Array.Empty<byte>(), FocasStatusMapper.Good);
+        var buf = new byte[byteCount];
+        for (var i = 0; i < byteCount; i++)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            var addr = new FocasAddress(FocasAreaKind.Pmc, letter, startByte + i, BitIndex: null, PathId: pathId);
+            var (value, status) = await ReadAsync(addr, FocasDataType.Byte, cancellationToken).ConfigureAwait(false);
+            if (status != FocasStatusMapper.Good) return (null, status);
+            buf[i] = value switch
+            {
+                sbyte s => unchecked((byte)s),
+                byte b => b,
+                int n => unchecked((byte)n),
+                short s => unchecked((byte)s),
+                _ => 0,
+            };
+        }
+        return (buf, FocasStatusMapper.Good);
+    }
 }
 
 /// <summary>