Add StreamOne/StreamMany/StreamAggregate helpers for Wolverine.Http.Marten

[jeremydmiller]

Summary

Closes #1562. Three new return-types that stream Marten JSON directly to the HTTP response, avoiding a deserialize/serialize round trip through .NET. Built on top of Marten.AspNetCore's existing JSON streaming helpers (WriteSingle/WriteArray/WriteLatest), with correct OpenAPI metadata contributed via IEndpointMetadataProvider.

API

// StreamOne<T> — single document via WriteSingle; 404 on no match
[WolverineGet(\"/invoices/{id}\")]
public static StreamOne<Invoice> Get(Guid id, IQuerySession session)
    => new(session.Query<Invoice>().Where(x => x.Id == id));

// StreamMany<T> — JSON array via WriteArray; empty array on no match
[WolverineGet(\"/invoices/approved\")]
public static StreamMany<Invoice> Approved(IQuerySession session)
    => new(session.Query<Invoice>().Where(x => x.Approved));

// StreamAggregate<T> — event-sourced latest aggregate via WriteLatest; 404 on unknown stream
[WolverineGet(\"/orders/{id}\")]
public static StreamAggregate<Order> Get(Guid id, IDocumentSession session)
    => new(session, id);

// Customize status code / content type
=> new(session.Query<Invoice>().Where(x => x.Id == cmd.InvoiceId))
   { OnFoundStatus = StatusCodes.Status201Created, ContentType = \"application/vnd.api+json\" };

Design notes

• No codegen plumbing needed. All three types implement IResult; Wolverine.Http's existing ResultWriterPolicy dispatches them naturally.
• OpenAPI via IEndpointMetadataProvider — Swashbuckle, NSwag, and the Minimal-API built-in OpenAPI generator all pick up correct 200: T/200: T[] + 404 responses without any extra registration.
• Root namespace Wolverine.Http.Marten (matches existing CompiledQueryWriterPolicy) for discoverability.
• StreamOne vs StreamAggregate explicitly distinguished in docs: StreamOne is for regular Marten documents (session.Query<T>()), StreamAggregate is for event-sourced aggregates (events.WriteLatest<T>, internally).

Scope boundaries

In scope: StreamOne<T>(IQueryable<T>), StreamMany<T>(IQueryable<T>), StreamAggregate<T>(IDocumentSession, Guid|string), OpenAPI metadata, custom status/content-type, tests, docs.

Deferred to follow-up: a parallel port for Polecat (Wolverine.Http.Polecat), to be opened as a separate PR once this lands.

Files

• New: StreamOne.cs, StreamMany.cs, StreamAggregate.cs in Wolverine.Http.Marten
• New: StreamingEndpoints.cs in WolverineWebApi/Marten (the Alba test host project)
• New: streaming_endpoints.cs in Wolverine.Http.Tests/Marten (12 tests)
• Modified: docs/guide/http/marten.md (new "Streaming JSON Responses" section with the StreamOne-vs-StreamAggregate distinction called out explicitly)

Test plan

• StreamOne: returns document + 200 + Content-Length + Content-Type on hit
• StreamOne: returns 404 on miss
• StreamOne: respects custom OnFoundStatus (tested at 202)
• StreamOne: respects custom ContentType (tested with vendor-specific type)
• StreamMany: returns JSON array
• StreamMany: returns empty array [] with 200 (not 404) on no match
• StreamAggregate: returns latest aggregate JSON for a valid stream
• StreamAggregate: returns 404 for unknown id
• OpenAPI metadata: StreamOne<T> advertises Produces<T> + 404
• OpenAPI metadata: StreamMany<T> advertises Produces<IReadOnlyList<T>>
• OpenAPI metadata: StreamAggregate<T> advertises Produces<T> + 404
• 20 existing Marten endpoint tests (compiled query writer, aggregate handler workflow) still pass

🤖 Generated with Claude Code