Vulthil.Messaging.Inbox.Cosmos

Azure Cosmos DB idempotency store for Vulthil.Messaging.Inbox.

Cosmos has no cross-partition transaction, so — unlike the relational store — it cannot commit the consumer's writes and the idempotency marker atomically. It provides effectively-once processing: best-effort deduplication of redeliveries over idempotent-by-design consumer writes.

When to use

• You use Vulthil.Messaging.Inbox and persist with the EF Core Cosmos provider

Pattern

• Your DbContext implements ISaveInboxMessages and applies the Cosmos inbox mapping via ApplyCosmosInbox()
• The marker is a self-contained document keyed + partitioned by MessageId in its own container; a duplicate insert conflicts and is treated as already-processed
• The marker is written after the consumer's own commit (no ambient transaction) — keep consumer writes idempotent

Usage

public sealed class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(options), ISaveInboxMessages
{
    public DbSet<InboxMessage> InboxMessages => Set<InboxMessage>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
        => modelBuilder.ApplyCosmosInbox();
}

builder.Services.AddCosmosInbox<AppDbContext>();

See the Inbox Pattern article for how the guarantees differ from the relational store.