Auto: focas-f2d — PMC range coalescing

Closes #266

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FakeFocasClient.cs

@@ -80,6 +80,33 @@ internal class FakeFocasClient : IFocasClient
         return Task.CompletedTask;
     }
 
+    /// <summary>
+    ///     Per-letter / per-path byte storage the coalesced range path reads from. Tests
+    ///     populate <c>PmcByteRanges[("R", 1)] = new byte[size]</c> + the corresponding values to
+    ///     drive both the per-tag <see cref="ReadAsync"/> + the coalesced
+    ///     <see cref="ReadPmcRangeAsync"/> path against the same source of truth (issue #266).
+    /// </summary>
+    public Dictionary<(string Letter, int PathId), byte[]> PmcByteRanges { get; } = new();
+
+    /// <summary>
+    ///     Ordered log of <c>pmc_rdpmcrng</c>-shaped range calls observed on this fake
+    ///     session — one entry per coalesced wire call. Tests assert this count to verify
+    ///     coalescing actually collapsed N per-byte reads into one range read (issue #266).
+    /// </summary>
+    public List<(string Letter, int PathId, int StartByte, int ByteCount)> RangeReadLog { get; } = new();
+
+    public virtual Task<(byte[]? buffer, uint status)> ReadPmcRangeAsync(
+        string letter, int pathId, int startByte, int byteCount, CancellationToken ct)
+    {
+        RangeReadLog.Add((letter, pathId, startByte, byteCount));
+        if (!PmcByteRanges.TryGetValue((letter.ToUpperInvariant(), pathId), out var src))
+            return Task.FromResult<(byte[]?, uint)>((new byte[byteCount], FocasStatusMapper.Good));
+        var buf = new byte[byteCount];
+        var copy = Math.Min(byteCount, Math.Max(0, src.Length - startByte));
+        if (copy > 0) Array.Copy(src, startByte, buf, 0, copy);
+        return Task.FromResult<(byte[]?, uint)>((buf, FocasStatusMapper.Good));
+    }
+
     public virtual void Dispose()
     {
         DisposeCount++;