GH-516 parity for HTTP: Before middleware can replace an immutable request body

[danniewalden]

Motivation

Handler chains have supported middleware replacing an immutable message since GH-516: a Before/BeforeAsync accepting the message type and returning it (optionally in a tuple) overwrites the message for the rest of the chain. HTTP chains lack the equivalent pass, so the same pattern on an endpoint class fails compilation with a colliding local (CS0841/CS0136):

public static Command Before(Command input, TimeProvider clock) =>
    input with { RejectedAt = clock.GetUtcNow() };

[WolverinePost("/reject")]
public static IResult Handle(Command command, State state) => ...;

Changes

Mirrors the HandlerChain.DetermineFrames GH-516 pass onto HttpChain.DetermineFrames (12 lines), with two HTTP-specific guards:

• skip chains with no request body
• skip the frame that reads the request body itself — the Newtonsoft reader is a MethodCall whose ReturnVariable is the request body variable; flipping it would delete the declaration

Sync, async, and tuple-returning Before methods behave identically to the handler side.

Out of scope

Registered middleware (Policies.AddMiddleware, [Middleware]) returning the request type is still blocked by the existing MiddlewarePolicy exception.

Tests

• middleware_replacing_immutable_request: Bug_516-style chained sync/async/tuple fact + tuple IResult short-circuit
• using_newtonsoft_for_serialization: regression for the body-reader skip
• Docs section in docs/guide/http/middleware.md

Full net9.0-pinned wolverine.slnx build clean; Wolverine.Http.Tests and CoreTests suites green.

🤖 Generated with Claude Code