Build Bobcat.Marten package — step-context extensions for Marten in specs

[jeremydmiller]

Goal

Add a Bobcat.Marten package mirroring the design of Bobcat.Alba — extension methods on IStepContext that look up an IDocumentStore (or IDocumentSession) via a marker resource interface, so fixture step methods can do Marten work without holding direct references.

This is item #2 in CONTEXT.md "Next Steps" and an enabler for the event-sourced samples (BankAccountES, MeetingGroupMonolith, BookingMonolith, several others).

Surface to deliver

namespace Bobcat.Marten;

public interface IMartenResource : ITestResource
{
    IDocumentStore DocumentStore { get; }
}

public class MartenResource : IMartenResource { ... }
public class MartenResource<TDocument> : IMartenResource { ... }  // optional: typed marker

public static class MartenStepContextExtensions
{
    // Document operations
    Task<T?> QueryByIdAsync<T>(this IStepContext context, object id, string? resourceName = null);
    Task<IReadOnlyList<T>> QueryAllAsync<T>(this IStepContext context, string? resourceName = null);
    Task StoreAsync<T>(this IStepContext context, T document, string? resourceName = null);
    Task DeleteByIdAsync<T>(this IStepContext context, object id, string? resourceName = null);

    // Event sourcing
    Task<IReadOnlyList<IEvent>> FetchStreamAsync(this IStepContext context, Guid streamId, string? resourceName = null);
    Task<T?> AggregateStreamAsync<T>(this IStepContext context, Guid streamId, string? resourceName = null);

    // Hygiene helpers for between-scenario reset (or for dedicated `[Given]` clean steps)
    Task CleanAllMartenDataAsync(this IStepContext context, string? resourceName = null);
    Task CompletelyRemoveAllAsync(this IStepContext context, string? resourceName = null);
}

IMartenResource.ResetBetweenScenarios() should default to CleanAllMartenDataAsync so spec runs start with a fresh database (overridable per-resource).

Considerations

• IDocumentStore lookup should not take a generic constraint — the existing pattern in IAlbaResource (marker interface, no generics) is the cleanest reuse.
• Don't try to abstract over IQuerySession vs IDocumentSession. The session is short-lived; helpers should open their own session per call (Marten's design encourages this).
• Helpers should accept an optional tenantId parameter once a sample needs multi-tenancy (defer until a sample drives it).
• Tests: replicate Bobcat.Alba.Tests style (~14 tests there). Cover resource lifecycle, Reset... semantics, and a couple of step-context lookup paths.
• Marten 8.32+ (the version Bobcat samples will pin to). Use Marten's primary surface; avoid deprecated MartenLinqQueryable casts (one of the things that bit us in CritterWatch testing this week).

Out of scope

• Combined patterns with Wolverine (tracked sessions + event store assertions). That's the next package, Bobcat.CritterStack.

Reference

• Existing analog: src/Bobcat.Alba/AlbaStepContextExtensions.cs and src/Bobcat.Alba/AlbaResource.cs
• Marten testing utilities to wrap: IDocumentStore.Advanced.Clean.CompletelyRemoveAllAsync, session.LoadAsync<T>(id), session.Events.FetchStreamAsync(streamId)