src/ prefix is omitted everywhere in this repo when specifying file paths, how?

[rinarakaki]

I'm wondering why it's supposed to work without src/ prefix for example,

in packages/core/package.json:

{
  "exports": {
    ".": {
      "types": "./index.d.ts",
      "import": "./index.js",
      "default": "./index.js"
    },
  }
}

but actually this must be:

{
  "exports": {
    ".": {
      "types": "./src/index.d.ts",
      "import": "./src/index.js",
      "default": "./src/index.js"
    },
  }
}

Another example is in packages/next-auth/test/env.test.ts:

import { reqWithEnvURL, setEnvDefaults } from "../lib/env"
import { setEnvDefaults as coreSetEnvDefaults } from "@auth/core"
import type { NextAuthConfig } from "../lib/index.js"

but actually this must be:

import { reqWithEnvURL, setEnvDefaults } from "../src/lib/env"
import { setEnvDefaults as coreSetEnvDefaults } from "@auth/core"
import type { NextAuthConfig } from "../src/lib/index.js"

Where are these behaviours configured? Thanks.