TDD: ObjectMeshDataSerializerTests + the shared ObjectMeshDataEquality
field-by-field comparator (reused by Task 6's equivalence suite) written
first, confirmed a compile failure against the not-yet-existing
ObjectMeshDataSerializer type.
Serializes EVERY field of the ObjectMeshData family per the plan's
normative layout: primitives raw LE, arrays as count:i32+payload,
blittable arrays (VertexPositionNormalTexture[], ushort[], byte[]) via
MemoryMarshal.AsBytes bulk copy, TextureBatches written sorted by the
(Width, Height, Format) key tuple for run-to-run determinism regardless
of dictionary insertion order, nullable fields as present:byte+value.
EnvCellGeometry nests recursively (MeshExtractor can populate one level
today; the serializer supports arbitrary depth rather than assuming it).
Namespace-trap finding: StagedEmitter.Emitter resolves to
DatReaderWriter.DBObjs.ParticleEmitter (the dat DBObj, verified via
reflection against the pinned Chorizite.DatReaderWriter 2.1.7 package
and confirmed live by MeshExtractor's `emitter.HwGfxObjId.DataId` call
site compiling), NOT AcDream.Core.Vfx.ParticleEmitter (the runtime
particle-simulation type with a live Particle[] pool that would NOT be
serializable asset data). All ~31 of its fields are written explicitly
rather than delegating to its own Pack/Unpack, which require a live
DatBinWriter/DatBinReader bound to a DatDatabase — coupling our pak's
determinism to a third-party wire-format helper we don't control the
versioning of.
33 tests green: 9 round-trip fixtures (empty/vertices+indices/multi
texture-batch-groups/setup-parts/emitters/nullable-present/nullable-
absent/edge-lines/nested-EnvCellGeometry), same-instance-twice byte-
identity, and dictionary-insertion-order-independence (two orders ->
identical bytes) plus a key-sort-order assertion on the raw bytes.
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