Auto: focas-f2d — PMC range coalescing

Closes #266

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

@@ -445,6 +445,42 @@ internal sealed class FwlibFocasClient : IFocasClient
         return (value, FocasStatusMapper.Good);
     }
 
+    /// <summary>
+    ///     Range read for the PMC coalescer (issue #266). FWLIB's <c>pmc_rdpmcrng</c>
+    ///     payload is capped at 40 bytes (the IODBPMC.Data union width), so requested
+    ///     ranges larger than that are chunked into 32-byte sub-calls internally —
+    ///     callers still see one logical range, which matches the
+    ///     <see cref="Wire.FocasPmcCoalescer"/>'s "one wire call per group" semantics.
+    /// </summary>
+    public Task<(byte[]? buffer, uint status)> ReadPmcRangeAsync(
+        string letter, int pathId, int startByte, int byteCount, CancellationToken cancellationToken)
+    {
+        if (!_connected) return Task.FromResult<(byte[]?, uint)>((null, FocasStatusMapper.BadCommunicationError));
+        cancellationToken.ThrowIfCancellationRequested();
+        if (byteCount <= 0) return Task.FromResult<(byte[]?, uint)>((Array.Empty<byte>(), FocasStatusMapper.Good));
+
+        var addrType = FocasPmcAddrType.FromLetter(letter)
+            ?? throw new InvalidOperationException($"Unknown PMC letter '{letter}'.");
+        var result = new byte[byteCount];
+        const int chunkBytes = 32;
+        var offset = 0;
+        while (offset < byteCount)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            var thisChunk = Math.Min(chunkBytes, byteCount - offset);
+            var buf = new FwlibNative.IODBPMC { Data = new byte[40] };
+            var ret = FwlibNative.PmcRdPmcRng(
+                _handle, addrType, FocasPmcDataType.Byte,
+                (ushort)(startByte + offset),
+                (ushort)(startByte + offset + thisChunk - 1),
+                (ushort)(8 + thisChunk), ref buf);
+            if (ret != 0) return Task.FromResult<(byte[]?, uint)>((null, FocasStatusMapper.MapFocasReturn(ret)));
+            Array.Copy(buf.Data, 0, result, offset, thisChunk);
+            offset += thisChunk;
+        }
+        return Task.FromResult<(byte[]?, uint)>((result, FocasStatusMapper.Good));
+    }
+
     private uint WritePmc(FocasAddress address, FocasDataType type, object? value)
     {
         var addrType = FocasPmcAddrType.FromLetter(address.PmcLetter ?? "") ?? (short)0;