Problem

The Request interface defines accepts, acceptsEncodings, acceptsCharsets, and acceptsLanguages with a single signature:

accepts: (...types: string[]) => string | boolean | string[]

This means TypeScript can't narrow the return type based on usage. Users must cast or type-guard every call:

// Current: always returns string | boolean | string[]
const type = req.accepts('json', 'html'); // string | boolean | string[]
// User has to cast: (type as string)

const all = req.accepts(); // string | boolean | string[] (should be string[])

The underlying Accepts class already handles all call patterns correctly and returns different types based on input.

Solution

Add TypeScript overload signatures that narrow the return type:

accepts: {
  (): string[]                           // no args = all accepted types
  (type: string): string | false         // single string = best match or false
  (types: string[]): string | false      // array = best match or false
  (...types: string[]): string | false   // variadic = best match or false
}

Also narrows AcceptsReturns from boolean to the literal false type, since these methods return false (not true) when no match is found. This matches Express's type definitions.

No runtime changes. The implementation already supports all call patterns. This is purely a type-narrowing improvement.

Changes

• packages/app/src/request.ts — Added overload signatures for all four accepts methods, narrowed AcceptsReturns to use false instead of boolean

Closes #396