HMR does not run when using turbopack and editing API route only

Describe the Bug

I noticed a subtle difference in behaviour when running the dev server with and without the --turbopack flag.
For reproduction I created a small payload plugin that adds a random value to the config.custom object.
When using turbopack payload.config.custom.instanceId always returns the initial value created by the plugin, even when the config is updated after a hot reload. When using webpack payload.config.custom.instanceId changes after every hot reload.

In the reproduction repo the current state can be queried using the /api endpoint.

When using webpack:

  ...
  "current": {
    "fromConfig": "9a834d7e-2c39-4b3b-82bd-eddcc16f2f9a",
    "fromConstant": "9a834d7e-2c39-4b3b-82bd-eddcc16f2f9a",
    "fromGetPayload": "9a834d7e-2c39-4b3b-82bd-eddcc16f2f9a",
    "fromGetPayloadCustom": "9a834d7e-2c39-4b3b-82bd-eddcc16f2f9a",
    "reload": 2
  },
  ...

All uuids are consistent after hot reload.

When using turbopack:

  ...
  "current": {
    "fromConfig": "bf7e319c-6d85-4164-a348-854646460273",
    "fromConstant": "efe59d14-9ffe-4c2d-a4f7-4cfbe6df843b",
    "fromGetPayload": "efe59d14-9ffe-4c2d-a4f7-4cfbe6df843b",
    "fromGetPayloadCustom": "efe59d14-9ffe-4c2d-a4f7-4cfbe6df843b",
    "reload": 2
  },
  ...

Here not all uuids are consistent after triggering a hot reload.

Link to the code that reproduces this issue

https://github.com/kenneth-devedis/payload-hotreload-issue

Reproduction Steps

• Clone Repository
• Create .env with existing db
• Repeat the following steps with pnpm dev:turbopack and pnpm dev:webpack
  • Reset the reload const in src/api/route.ts
  • Start the dev server
  • Call /api (curl http://localhost:3000/api)
  • (Recalling the api results in a unchanged response)
  • Change reload in src/api/route.ts manually to another value to trigger hot reloading
  • Call /api again
• Compare the results (See Readme.md for examples)

Which area(s) are affected? (Select all that apply)

area: core

Environment Info

Binaries:
  Node: 22.16.0
  npm: 10.9.2
  Yarn: N/A
  pnpm: 10.8.0
Relevant Packages:
  payload: 3.43.0
  next: 15.3.0
  @payloadcms/db-postgres: 3.43.0
  @payloadcms/email-nodemailer: 3.43.0
  @payloadcms/graphql: 3.43.0
  @payloadcms/next/utilities: 3.43.0
  @payloadcms/payload-cloud: 3.43.0
  @payloadcms/richtext-lexical: 3.43.0
  @payloadcms/translations: 3.43.0
  @payloadcms/ui/shared: 3.43.0
  react: 19.1.0
  react-dom: 19.1.0
Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.5.0: Tue Apr 22 19:54:49 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T6000
  Available memory (MB): 32768
  Available CPU cores: 10