Add support for nested proxy.ts files inside Route Groups

[ahmedmbarektorjmene]

Goals

1. Enable proxy.ts files to be colocated within nested Route Groups (e.g., app/(auth)/proxy.ts, app/(admin)/proxy.ts).
2. Improve modularity and separation of concerns for server-side proxying, auth, and cross-cutting concerns per route segment.
3. Reduce duplication and conditional logic in a single, global proxy.ts by allowing scoped behavior.

Non-Goals

1. This proposal does not change the routing semantics or URL structure of Route Groups.
2. This proposal does not introduce new client-side APIs or UI-related behavior.
3. This proposal does not replace existing middleware; it complements current patterns.

Background

Today, Next.js encourages colocation via the App Router, Route Groups, and nested layouts. However, server-side proxying (e.g., request forwarding, auth token injection, header normalization, or environment-based routing) is typically centralized in a single root-level construct. This creates friction when different route groups require distinct proxy behavior (for example, (auth) vs (admin) vs (public) routes).

Current alternatives include:

• A monolithic proxy.ts with complex conditional logic based on pathname.
• Multiple custom route handlers duplicating proxy logic.
• Middleware-based solutions that are broader in scope than necessary and can be harder to reason about or optimize.

These approaches reduce clarity and break the otherwise strong colocation model of the App Router.

Proposal

Allow proxy.ts to be discovered and applied hierarchically within the app/ directory, similar to layout.tsx and loading.tsx:

• A proxy.ts placed inside a Route Group or route segment applies only to that subtree.
• Resolution follows nearest-ancestor wins, with an optional ability to compose or extend from parent proxies.
• The root-level app/proxy.ts (if present) acts as the default fallback.

Example

proxy.ts                // global/default proxy
app/
  (auth)/
    proxy.ts              // auth-specific proxy behavior
    login/
      route.ts
  (admin)/
    proxy.ts              // admin-specific proxy behavior
    dashboard/
      route.ts