Add lightweight EF Core tenant guardrails sample

[balajibashyam]

Summary

Adds a minimal .NET 10 companion sample for the EF Core 8 Multi-Tenancy: Tenant Isolation, Soft Deletes, Audit Trails & Query Filters tutorial.

The tutorial is EF Core 8-era and broad; this companion is EF Core 10 and narrowly answers: how can EF Core make shared-table tenant reads fail closed, keep soft-delete bypass tenant-safe, reject cross-tenant writes, and prove those guardrails against one relational database containing multiple tenants at the same time?

What's included

• New sample: ef-core/multitenancy-softdelete-auditing/ — 13 files

  • Validated, trusted TenantExecutionContext injected into every DbContext
  • Fail-closed named TenantFilter (always active)
  • Named SoftDeleteFilter with selective bypass that keeps the tenant filter active
  • Composite primary key TenantId + Id so alpha/1 and beta/1 coexist
  • SaveChangesInterceptor (sync + async) that overwrites insert tenant, rejects cross-tenant mutations, stamps creation/update audit, and converts Remove() to a narrow soft-delete update
  • One shared SQLite in-memory database hosting both alpha and beta tenants
  • 8 deterministic xUnit v3 integration tests

• Root README: New sample row in the table + updated repository structure tree

• GitHub Actions: New test-ef-core-tenant-guardrails job in the shared workflow; path filters updated for push and pull_request

Deliberately omitted (stays in the full tutorial)

HTTP tenant resolution, subdomain parsing, JWT/authentication, tenant membership lookup, platform-admin all-tenant access, background jobs, hard delete, GDPR workflows, PostgreSQL RLS / SQL Server security policies, migrations, compiled queries, ExecuteUpdate/ExecuteDelete, Minimal APIs, repositories, Testcontainers, benchmarks.

Versions

• .NET SDK: 10.0.302
• Microsoft.EntityFrameworkCore.Sqlite: 10.0.11 (only direct app package)
• xunit.v3 3.2.2, xunit.runner.visualstudio 3.1.5, Microsoft.NET.Test.Sdk 18.8.1

Validation

• dotnet restore — passed
• dotnet build --configuration Release — passed (0 errors, 0 warnings)
• dotnet test --configuration Release — passed (8/8)
• App output matches the exact six-line expected block
• Security scan — clean
• No generated SQLite database artifacts