Duplicate SWC transform for use client components when React Compiler is disabled

Link to the code that reproduces this issue

https://github.com/canyon-project/nextjs16-swc-duplicate-compilation

To Reproduce

1. pnpm i
2. npm run build
3. look .swc-plugin-stage-output

Current vs. Expected behavior

After testing the Next.js + Turbopack combination, we observed duplicate identical filenames appearing in the SWC AST during compilation. Our investigation identified that this behavior is inherent to Next.js' compilation workflow.
To address this ambiguity (consistent with Vite's pattern), we propose appending a layer query parameter to the filename passed to SWC (via TransformContext) — e.g., app/page.tsx?layer=app-rsc — to enable SWC plugins to distinguish between these duplicate entries.
For extensibility (aligned with next-swc-loader), we use a named parameter format:

• Use ?layer=value for paths with no existing query string
• Use &layer=... for paths that already contain a query string

Expected behavior

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.0.0: Wed Sep 17 21:41:45 PDT 2025; root:xnu-12377.1.9~141/RELEASE_ARM64_T6000
  Available memory (MB): 16384
  Available CPU cores: 8
Binaries:
  Node: 25.2.1
  npm: 11.6.2
  Yarn: N/A
  pnpm: 10.13.0
Relevant Packages:
  next: 16.1.6 // Latest available version is detected (16.1.6).
  eslint-config-next: N/A
  react: 19.2.3
  react-dom: 19.2.3
  typescript: 5.9.3
Next.js Config:
  output: N/A

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

SWC

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

next build (local)

Additional context

Start with the linked reproduction: run pnpm i and npm run build, then inspect .swc-plugin-stage-output to confirm the duplicate entries. Trace the filename passed to SWC through TransformContext and next-swc-loader, including existing query strings. Done means duplicate transforms can be distinguished by the specified layer parameter.