Validate Kind Override Compatibility

[j-d-ha]

Priority: P2 - Important
Tier: 3 - Advanced Features
Effort: Medium (4-6 hours)

Already In Codebase

• [DynamoField(Kind = ...)] is already parsed and threaded into generated calls.
  • Parsing: src/LayeredCraft.DynamoMapper.Generators/MapperSyntaxProvider.cs
  • Strategy selection + kind threading: src/LayeredCraft.DynamoMapper.Generators/PropertyMapping/TypeMappingStrategyResolver.cs and src/LayeredCraft.DynamoMapper.Generators/PropertyMapping/PropertyMappingSpecBuilder.cs
• The generator currently rejects Phase-2 collection kinds (L/M/SS/NS/BS) with DM0001 (CannotConvertFromAttributeValue).
• There is a snapshot test demonstrating kind override usage: test/LayeredCraft.DynamoMapper.Generators.Tests/DynamoFieldVerifyTests.cs.

Goal

Add compatibility validation and diagnostics for Kind overrides.

Today kind overrides are effectively "pass-through" (codegen compiles) but can lead to runtime NotImplementedException (e.g., DynamoKind.B) or confusing parsing behavior.

Scope

• Validate that Kind overrides are compatible with the CLR property type and the runtime extension methods.
• Emit generator diagnostics (rather than letting invalid combinations fail at runtime).

Examples

• string + DynamoKind.S is valid.
• string + DynamoKind.B should emit a diagnostic until binary support is implemented.
• Guid + DynamoKind.S and Guid + DynamoKind.N may be allowed, but should be intentionally validated.

Implementation notes

• Add a validator (e.g., KindValidator) that runs after type strategy resolution.
• Expand diagnostics beyond DM0001 for invalid kind override combinations.
• Keep the current behavior of rejecting L/M/SS/NS/BS until Story 5.1 (collections) is implemented.

Acceptance criteria

• Invalid kind overrides produce clear compile-time diagnostics.
• Valid kind overrides continue to generate correct code.
• Tests cover at least one valid and one invalid kind override.