feat(stage3): scaffold task-001 baseline

- WHY: establish Stage 3 task-001 execution baseline per repo intent
- WHAT: add minimal solution/project skeleton and boundary docs
- RULE: apply stage3 execution runtime and repository workflow directives

Furniture.DAL.slnx

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+<Solution>
+  <Folder Name="/src/">
+    <Project Path="src/Furniture.DAL/Furniture.DAL.csproj" />
+  </Folder>
+  <Folder Name="/tests/">
+    <Project Path="tests/Furniture.DAL.UnitTests/Furniture.DAL.UnitTests.csproj" />
+  </Folder>
+</Solution>

docs/architecture/dal-layer-map.puml

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+@startuml
+skinparam packageStyle rectangle
+
+package "furniture-dal" {
+  interface IFurnitureDataProvider
+  interface ICatalogDataProvider
+  interface IFurnitureRepository
+  interface ICatalogRepository
+  interface ICacheInvalidationPolicy
+
+  IFurnitureRepository --> IFurnitureDataProvider
+  ICatalogRepository --> ICatalogDataProvider
+  IFurnitureRepository --> ICacheInvalidationPolicy
+  ICatalogRepository --> ICacheInvalidationPolicy
+}
+
+package "furniture-service" as FurnitureService
+FurnitureService --> IFurnitureRepository
+FurnitureService --> ICatalogRepository
+@enduml

docs/dal/persistence-cache-policy.md

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+# DAL Persistence and Cache Policy
+
+## Responsibilities
+
+- Repositories coordinate provider calls for aggregate persistence.
+- Cache invalidation policy is owned by DAL.
+- Service layer does not implement persistence or cache invalidation details.
+
+## Policy
+
+- Persistence writes must define cache invalidation triggers.
+- Cache keys and invalidation behavior are centralized in DAL policy definitions.

docs/dal/provider-boundaries.md

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+# DAL Provider Boundaries
+
+## Ownership
+
+- `IFurnitureDataProvider`: furniture persistence provider boundary.
+- `ICatalogDataProvider`: catalog persistence provider boundary.
+
+## Rules
+
+- Providers encapsulate datastore-specific access.
+- Providers do not contain orchestration concerns.
+- Provider contracts are consumed by DAL repositories.

src/Furniture.DAL/Caching/ICacheInvalidationPolicy.cs

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+namespace Furniture.DAL.Caching;
+
+/// <summary>
+/// Defines cache invalidation policy boundary for DAL operations.
+/// </summary>
+public interface ICacheInvalidationPolicy
+{
+}

src/Furniture.DAL/Furniture.DAL.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+</Project>

src/Furniture.DAL/Providers/ICatalogDataProvider.cs

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+namespace Furniture.DAL.Providers;
+
+/// <summary>
+/// Defines provider access for catalog persistence operations.
+/// </summary>
+public interface ICatalogDataProvider
+{
+}

src/Furniture.DAL/Providers/IFurnitureDataProvider.cs

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+namespace Furniture.DAL.Providers;
+
+/// <summary>
+/// Defines provider access for furniture persistence operations.
+/// </summary>
+public interface IFurnitureDataProvider
+{
+}

src/Furniture.DAL/Repositories/ICatalogRepository.cs

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+namespace Furniture.DAL.Repositories;
+
+/// <summary>
+/// Defines catalog aggregate repository boundary owned by DAL.
+/// </summary>
+public interface ICatalogRepository
+{
+}

src/Furniture.DAL/Repositories/IFurnitureRepository.cs

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+namespace Furniture.DAL.Repositories;
+
+/// <summary>
+/// Defines furniture aggregate repository boundary owned by DAL.
+/// </summary>
+public interface IFurnitureRepository
+{
+}

tests/Furniture.DAL.UnitTests/BoundaryShapeTests.cs

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+using Furniture.DAL.Caching;
+using Furniture.DAL.Providers;
+using Furniture.DAL.Repositories;
+
+namespace Furniture.DAL.UnitTests;
+
+public class BoundaryShapeTests
+{
+    [Fact]
+    public void ProviderBoundaries_WhenReflected_AreInterfaces()
+    {
+        Assert.True(typeof(IFurnitureDataProvider).IsInterface);
+        Assert.True(typeof(ICatalogDataProvider).IsInterface);
+    }
+
+    [Fact]
+    public void RepositoryAndCacheBoundaries_WhenReflected_AreInterfaces()
+    {
+        Assert.True(typeof(IFurnitureRepository).IsInterface);
+        Assert.True(typeof(ICatalogRepository).IsInterface);
+        Assert.True(typeof(ICacheInvalidationPolicy).IsInterface);
+    }
+}

tests/Furniture.DAL.UnitTests/Furniture.DAL.UnitTests.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+  </ItemGroup>
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Furniture.DAL\Furniture.DAL.csproj" />
+  </ItemGroup>
+</Project>