Output Caching support for Wolverine.HTTP endpoints

[jeremydmiller]

Summary

Wolverine.HTTP currently supports [ResponseCache] for client-side cache headers but has no integration with ASP.NET Core's server-side output caching middleware. There's no way to declaratively apply output caching to a Wolverine endpoint.

Proposal

Add output caching support to Wolverine.HTTP via:

1. New attribute — e.g. [WolverineOutputCache] or [CachedResponse] that can be applied to endpoint methods to opt into server-side output caching with policy configuration (duration, vary-by, tags for invalidation)
2. New Wolverine.HTTP middleware — code-generated middleware that integrates with ASP.NET Core's OutputCacheMiddleware infrastructure, handling cache storage and retrieval
3. Integration with [Entity] loader and persistence codegen — the output caching middleware must be aware of existing entity loading patterns. If an endpoint uses [Entity] or other persistence loading attributes, the caching layer needs to:
   • Short-circuit entity loading on cache hits (avoid unnecessary DB queries)
   • Properly integrate with the code generation pipeline so the cache check runs before persistence loading in the generated handler code
4. Tag-based cache invalidation — ability to invalidate cached responses when related data changes (e.g. via message handlers or side effects)

Implementation Considerations

• The code generation must place the cache check before any [Entity]/persistence loading in the generated pipeline to avoid unnecessary database round-trips on cache hits
• Should support ASP.NET Core's existing output cache policies and tag-based eviction
• Consider how this interacts with multi-tenancy (tenant-specific cache keys)
• Consider interaction with authorization (authenticated vs anonymous caching)
• ETag/conditional request support (304 Not Modified) would be a natural companion feature

Context

All comparable frameworks support output caching:

• Minimal APIs: built-in .CacheOutput() with policies, tag-based invalidation (.NET 7+)
• MVC: [OutputCache] attribute with the same middleware
• FastEndpoints: uses ASP.NET Core output caching middleware directly

Output caching can dramatically reduce load for read-heavy endpoints and is a commonly expected feature for production APIs.

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