feat: IIdempotencyStore – EF Core implementation

[samtrion]

User Story

As a developer using EF Core with Pulse, I want a fully functional IIdempotencyStore backed by Entity Framework Core, so that I can prevent duplicate command execution using my existing DbContext without adopting a separate ADO.NET provider.

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Background

IIdempotencyStore and IdempotencyCommandInterceptor are implemented, but no concrete store exists. Without a registered IIdempotencyStore, the interceptor is a no-op and idempotency is not enforced. An EF Core implementation integrates naturally with applications that already use EF for persistence, sharing the same DbContext transaction scope.

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Requirements

• Define IdempotencyKeySchema constants in NetEvolve.Pulse.Extensibility (schema name, table name, column names, max lengths).
• Define IIdempotencyStoreDbContext in NetEvolve.Pulse.EntityFramework: DbSet<IdempotencyKey> IdempotencyKeys { get; }.
• Create IdempotencyKey POCO in NetEvolve.Pulse.EntityFramework: string IdempotencyKey (PK), DateTimeOffset CreatedAt.
• Create IdempotencyKeyOptions in NetEvolve.Pulse.EntityFramework: Schema, TableName, TimeToLive?.
• Create abstract IdempotencyKeyConfigurationBase : IEntityTypeConfiguration<IdempotencyKey> with provider-overridable column types.
• Create provider-specific configurations: SqlServerIdempotencyKeyConfiguration, PostgreSqlIdempotencyKeyConfiguration, SqliteIdempotencyKeyConfiguration.
• Implement EntityFrameworkIdempotencyStore<TContext> : IIdempotencyStore:
  • ExistsAsync: compiled query AnyAsync(k => k.IdempotencyKey == key), respecting TimeToLive when set.
  • StoreAsync: insert new IdempotencyKey; handle duplicate-key exception as idempotent (return without throwing).
• Expose AddEntityFrameworkIdempotencyStore<TContext>(this IMediatorBuilder, Action<IdempotencyKeyOptions>?) extension method.

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Acceptance Criteria

• IdempotencyKeySchema constants match the schema expected by all provider configurations.
• EntityFrameworkIdempotencyStore.ExistsAsync returns true for an existing key and false for a new one.
• When TimeToLive is set, expired keys are treated as absent.
• StoreAsync does not throw when a duplicate key is inserted concurrently.
• AddEntityFrameworkIdempotencyStore<TContext>() registers IIdempotencyStore as Scoped.
• Unit tests cover: key exists, key absent, TTL expiry, duplicate insert, options wiring.

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Out of Scope

• ADO.NET implementations (tracked per-provider in separate issues).
• TTL-based cleanup jobs.