feat(phase-1): frame codec — TcrMessage / TcrPart / BigEndian{Reader,Writer}

[TomiCheng]

Summary

Phase 1 frame codec — pure encode/decode of TcrMessage ↔ bytes. All MVP wire-format primitives in place. No sockets yet.

Phase / Roadmap

• Phase: Phase 1 — Frame codec (closes Phase 1: Implement frame codec (encode/decode TcrMessage) #2)

Changes

Phase 1 codec (src/Geode.Client/Protocol/)

• MessageType — enum mirroring cppcache/src/TcrMessage.hpp::enum MsgType in full (99 wire values + 2 sentinels). PascalCase, dropped redundant _MSG_TYPE / _TYPE suffixes. Numeric gaps (57, 95, 101, 102, 104) preserved.
• BigEndianBinaryWriter — sequential big-endian writer over an internal MemoryStream. C# counterpart of cppcache DataOutput. Implemented: WriteByte / WriteBool / WriteInt32 / WriteInt64 / WriteBytesOnly. Stubs (NotImplementedException with phase markers) for WriteSByte / WriteInt16 / WriteUInt16/32/64 / WriteFloat / WriteDouble / WriteBytes / WriteArrayLen / WriteJavaModifiedUtf8 / WriteUtf16Huge.
• BigEndianBinaryReader — symmetric reader over ReadOnlyMemory<byte>, with zero-copy ReadBytesOnly. Throws EndOfStreamException on overrun.
• TcrPart record — i32 length + u8 IsObject + ReadOnlyMemory<byte> Payload. Custom Equals / GetHashCode for byte-content equality (record default would be reference-based on ReadOnlyMemory).
• TcrMessage record — 17-byte header (msgType / msgLength / numParts / txId / earlyAck) + Parts. Two-pass Encode (parts first to learn length, then header + parts). Decode strict-validates MessageLength matches actual parts byte count and NumParts >= 0.
• Removed _Phase1Placeholder.cs.

Repo plumbing carried on this branch

• NuGet.config — <clear/> + nuget.org only, fixes NU1507 on machines with extra sources configured at user / machine level (CPM requires either single source or explicit mapping).
• Directory.Build.props — AnalysisLevel relaxed from latest-recommended to latest-default during MVP. TODO marker to tighten back before Phase 5 / first NuGet release. Fixed CHANGE_ME → real GitHub URL.
• samples/.../Program.cs — added missing using Microsoft.Extensions.DependencyInjection; (CS1061 fix).
• tests/.../GeodeFixture.cs — [SuppressMessage("Naming", "CA1711")] on GeodeCollection (xUnit [CollectionDefinition(nameof(...))] convention requires the class name).
• geode-dotnet.sln — VS 2022 added src / test / sample solution folders and version stamps.
• Dropped FluentAssertions across the repo. v8.x changed to a non-OSI Xceed license; instead of auditing the new terms for our Apache-2.0 use case, removed the dependency entirely. xUnit native Assert.* covers everything we used. Phase 0 SmokeTests / GeodeContainerSmokeTests also converted.
• Routine dependency bumps via VS auto-update: Microsoft.NET.Test.Sdk 17.12 → 18.5.1, xunit.v3 1.0 → 3.2.2, xunit.runner.visualstudio 3.0 → 3.1.5, coverlet.collector 6.0.2 → 10.0.0.
• .gitignore — ignore .cr/ (VS 2022 extension cache).

Tests

• Unit tests — 4 new files under tests/Geode.Client.Tests/Protocol/ (~34 facts):
  • BigEndianBinaryWriterTests — primitives, concat, length tracking.
  • BigEndianBinaryReaderTests — primitives, zero-copy slice (verified by mutating source array), bounds, position tracking.
  • TcrPartTests — round-trip (simple / empty / isObject), validation, content-based equality.
  • TcrMessageTests — round-trip + byte-fixture tests for Ping (17 bytes) and Put-with-byte-part (23 bytes), derived from cppcache wire format (cite writeHeader / writeMessageLength / writeBytePart line numbers in code comments). Validation: negative NumParts, MessageLength mismatch.
• New / updated integration tests — N/A for Phase 1 (no socket yet).
• Existing tests still pass — Phase 0 SmokeTests + GeodeContainerSmokeTests now use Assert.* after FA removal.

Notes for reviewer

• Buffer-based codec design committed long-term. Reader takes ReadOnlyMemory<byte>, Writer owns internal buffer + ToArray(). Aligns with modern .NET codec patterns (System.Text.Json, MessagePack-CSharp, System.IO.Pipelines): codec is sync over Memory/Span; async lives at the I/O boundary (Phase 2's TcpConnection).
• CI is currently disabled (see CONTRIBUTING.md §5.3); local VS build was the only validation. Re-enable target: before Phase 5 / first NuGet preview.
• This branch carries non-Phase-1 chore commits (analyzer relax, NuGet config, FA removal, deps). They surfaced during Phase 1 development and were not worth a separate branch given solo-dev / CI-off context. Future feature branches will be tighter.
• Phase 0 has a known wire-format claim about Part containing a separate Type byte — verified against cppcache/src/TcrMessage.cpp line 812-816 that Part is 3 fields: length / isObject / payload (the C++ Type is the first byte of payload when isObject=1). This implementation matches the actual cppcache code.