fix(next): Ensure inline sourcemaps are generated for wrapped modules in Dev

[logaretm]

This fixes breakpoints for editors like VSCode/Cursor in server-side code.

I have verified that breakpoints work in:

• Server-side app router components
• Server-side pages router functions and static params
• API endpoints and server-side functions
• middleware

This only affects webpack, and doesn't change anything for prod builds.

closes #17088

[linear]

JS-753 Ensure debugging server-side code (app router) in VSCode works

[github-actions]

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	8,875	-	9,079	-2%
GET With Sentry	1,760	20%	1,730	+2%
GET With Sentry (error only)	6,095	69%	6,112	-0%
POST Baseline	1,204	-	1,170	+3%
POST With Sentry	602	50%	561	+7%
POST With Sentry (error only)	1,069	89%	1,032	+4%
MYSQL Baseline	3,329	-	3,198	+4%
MYSQL With Sentry	493	15%	400	+23%
MYSQL With Sentry (error only)	2,739	82%	2,584	+6%

View base workflow run

[Copilot]

Pull request overview

This PR fixes debugger breakpoint support in development mode for Next.js server-side code by generating inline sourcemaps in the wrapping loader. The changes ensure that IDEs like VSCode and Cursor can correctly map breakpoints back to the original source files for server components, API routes, middleware, and other server-side code.

• Adds isDev parameter to wrapping loader options and passes it through webpack configuration
• Modifies sourcemap generation to use inline sourcemaps in dev mode and hidden sourcemaps in production
• Implements absolute path preservation in dev mode sourcemaps to ensure correct breakpoint resolution
• Adds test coverage for both dev and production sourcemap behavior

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
packages/nextjs/src/config/webpack.ts	Adds isDev flag to staticWrappingLoaderOptions to pass development mode state to the wrapping loader
packages/nextjs/src/config/loaders/wrappingLoader.ts	Implements inline sourcemap generation for dev mode, including logic to preserve absolute paths and create identity mappings when no sourcemap exists
packages/nextjs/test/config/wrappingLoader.test.ts	Adds test coverage for inline sourcemap presence in dev mode and absence in production mode

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[chargome]

Looks good!