Cosmos DB Provider

Non-relational provider with its own parallel query pipeline. Uses JSON for document materialization.

Key Differences from Relational

• No migrations — use EnsureCreated()
• Documents as JSON — owned and complex types become embedded objects
• Partition key configuration required for performance
• ETag for optimistic concurrency
• No cross-container joins

Azure Cosmos DB Emulator for Tests

• TestEnvironment.InitializeAsync() auto-starts a Testcontainers.CosmosDb container when Test__Cosmos__DefaultConnection is not set. Set the env var to use an existing emulator instead.
• Skip tests requiring unsupported features on the Linux emulator with [ConditionalFact(typeof(CosmosTestEnvironment), nameof(CosmosTestEnvironment.IsNotLinuxEmulator))].