False positive for the "Server Actions must be async functions." diagnostic when using builder pattern with arrow function

[ChristianIvicevic]

Link to the code that reproduces this issue

https://github.com/ChristianIvicevic/debug/tree/turbopack-async-arrow-function

To Reproduce

1. pnpm install
2. pnpm dev
3. Attempt to open the root page and see the false positive

Current vs. Expected behavior

Current behavior

Extracting that inlined schema into a separate object does work and won't trigger the false positive.

Expected behavior

Being able to inline the schema here which is the cause of the false positive:

export const $serverAction = actionClient
	.schema(
		z.object({
			things: z.enum(Object.entries(things).map(([kind]) => kind) as [string, ...string[]]),
		}),
	)
	.action(async () => {})

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.3.0: Thu Jan  2 20:24:23 PST 2025; root:xnu-11215.81.4~3/RELEASE_ARM64_T6031
  Available memory (MB): 49152
  Available CPU cores: 16
Binaries:
  Node: 22.14.0
  npm: 10.9.2
  Yarn: N/A
  pnpm: 10.7.1
Relevant Packages:
  next: 15.2.4 // Latest available version is detected (15.2.4).
  eslint-config-next: N/A
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.8.3
Next.js Config:
  output: N/A

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

Turbopack, Server Actions

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

next dev (local)

Additional context

No response