FOCAS Tier-C PR A — Driver.FOCAS.Shared MessagePack IPC contracts. First PR of the 5-PR #220 split (isolation plan at docs/v2/implementation/focas-isolation-plan.md). Adds a new netstandard2.0 project consumable by both the .NET 10 Proxy and the future .NET 4.8 x86 Host, carrying every wire DTO the Proxy <-> Host pair will exchange: Hello/HelloAck + Heartbeat/HeartbeatAck + ErrorResponse for session negotiation (shared-secret + protocol major/minor mirroring Galaxy.Shared); OpenSessionRequest/Response + CloseSessionRequest carrying the declared FocasCncSeries so the Host picks up the pre-flight matrix; FocasAddressDto + FocasDataTypeCode for wire-compatible serialization of parsed addresses (0=Pmc/1=Param/2=Macro matches FocasAreaKind enum order so both sides cast (int)); ReadRequest/Response + WriteRequest/Response with MessagePack-serialized boxed values tagged by FocasDataTypeCode; PmcBitWriteRequest/Response as a first-class RMW operation so the critical section stays Host-side; Subscribe/Unsubscribe/OnDataChangeNotification for poll-loop-pushes-deltas model (FOCAS has no CNC-initiated callbacks); Probe + RuntimeStatusChange + Recycle surface for Tier-C supervision. Framing is [4-byte BE length][1-byte kind][body] with 16 MiB body cap matching Galaxy; FocasMessageKind byte values align with Galaxy ranges so an operator reading a hex dump doesn't have to context-switch. FrameReader/FrameWriter ported from Galaxy.Shared with thread-safe concurrent-write serialization. 24 new unit tests: 18 per-DTO round-trip tests covering every field + 6 framing tests (single-frame round-trip, clean-EOF returns null, oversized-length rejection, mid-frame EOF throws, 20-way concurrent-write ordering preserved, MessageKind byte values locked as wire-stable). No driver changes; existing 165 FOCAS unit tests still pass unchanged. PR B (Host skeleton) goes next.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared/Contracts/ReadWrite.cs

@@ -0,0 +1,85 @@
+using MessagePack;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;
+
+/// <summary>
+///     Read one FOCAS address. Multi-read is the Proxy's responsibility — it batches
+///     per-tag reads into parallel <see cref="ReadRequest"/> frames the Host services on its
+///     STA thread. Keeping the IPC read single-address keeps the Host side trivial; FOCAS
+///     itself has no multi-read primitive that spans area kinds.
+/// </summary>
+[MessagePackObject]
+public sealed class ReadRequest
+{
+    [Key(0)] public long SessionId { get; set; }
+    [Key(1)] public FocasAddressDto Address { get; set; } = new();
+    [Key(2)] public int DataType { get; set; }
+    [Key(3)] public int TimeoutMs { get; set; } = 2000;
+}
+
+[MessagePackObject]
+public sealed class ReadResponse
+{
+    [Key(0)] public bool Success { get; set; }
+    [Key(1)] public string? Error { get; set; }
+
+    /// <summary>OPC UA status code mapped by the Host via <c>FocasStatusMapper</c> — 0 = Good.</summary>
+    [Key(2)] public uint StatusCode { get; set; }
+
+    /// <summary>MessagePack-serialized boxed value. <c>null</c> when <see cref="Success"/> is false.</summary>
+    [Key(3)] public byte[]? ValueBytes { get; set; }
+
+    /// <summary>Matches <see cref="FocasDataTypeCode"/> so the Proxy knows how to deserialize.</summary>
+    [Key(4)] public int ValueTypeCode { get; set; }
+
+    [Key(5)] public long SourceTimestampUtcUnixMs { get; set; }
+}
+
+[MessagePackObject]
+public sealed class WriteRequest
+{
+    [Key(0)] public long SessionId { get; set; }
+    [Key(1)] public FocasAddressDto Address { get; set; } = new();
+    [Key(2)] public int DataType { get; set; }
+    [Key(3)] public byte[]? ValueBytes { get; set; }
+    [Key(4)] public int ValueTypeCode { get; set; }
+    [Key(5)] public int TimeoutMs { get; set; } = 2000;
+}
+
+[MessagePackObject]
+public sealed class WriteResponse
+{
+    [Key(0)] public bool Success { get; set; }
+    [Key(1)] public string? Error { get; set; }
+
+    /// <summary>OPC UA status code — 0 = Good.</summary>
+    [Key(2)] public uint StatusCode { get; set; }
+}
+
+/// <summary>
+///     PMC bit read-modify-write. Handled as a first-class operation (not two separate
+///     read+write round-trips) so the critical section stays on the Host — serializing
+///     concurrent bit writers to the same parent byte is Host-side via
+///     <c>SemaphoreSlim</c> keyed on <c>(PmcLetter, Number)</c>. Mirrors the in-process
+///     pattern from <c>FocasPmcBitRmw</c>.
+/// </summary>
+[MessagePackObject]
+public sealed class PmcBitWriteRequest
+{
+    [Key(0)] public long SessionId { get; set; }
+    [Key(1)] public FocasAddressDto Address { get; set; } = new();
+
+    /// <summary>The bit index to set/clear. 0-7.</summary>
+    [Key(2)] public int BitIndex { get; set; }
+
+    [Key(3)] public bool Value { get; set; }
+    [Key(4)] public int TimeoutMs { get; set; } = 2000;
+}
+
+[MessagePackObject]
+public sealed class PmcBitWriteResponse
+{
+    [Key(0)] public bool Success { get; set; }
+    [Key(1)] public string? Error { get; set; }
+    [Key(2)] public uint StatusCode { get; set; }
+}