[Next.js] Add App Router route resolver

[theDakshJaitly]

Target branch: code-graph-preview

Dependency

The TypeScript and JavaScript extractors are already available on code-graph-preview. No language-extractor issue blocks this resolver.

Goal

Add a bounded Next.js resolver for App Router route handlers. The first version should translate file-based route modules into route nodes and connect exported HTTP handler functions without attempting to model the full Next.js routing system.

Scope

• Detect Next.js through next in dependencies or dev dependencies.
• Recognize app/**/route.ts and app/**/route.js, including projects using src/app/.
• Recognize exported GET, POST, PUT, PATCH, DELETE, OPTIONS, and HEAD handler functions.
• Derive a route path from the directory containing the route file.
• Preserve dynamic segment text such as [id] in the first version.
• Emit one route node per exported HTTP handler and a reference to that handler function.
• Resolve each route to the corresponding same-file function when unambiguous.

Required changes

• Add src/graph/resolution/frameworks/nextjs.ts implementing FrameworkResolver.
• Register and export it from src/graph/resolution/frameworks/index.ts.
• Add minimal App Router fixtures for TypeScript and JavaScript.
• Add focused detection, path derivation, extraction, resolution, and ambiguity tests.

Acceptance criteria

• Positive and negative Next.js detection are tested.
• Both app/ and src/app/ roots are covered.
• Tests cover multiple HTTP methods, a nested static path, and a dynamic segment.
• Route nodes use stable ids and the source file's language id.
• Only explicitly exported HTTP handler names create route nodes.
• Missing or ambiguous handler functions remain unresolved.
• The resolver is additive and does not change the frozen interface.
• npm run typecheck, npm test, and npm run build pass.

Out of scope

• Pages Router API routes.
• Route groups, parallel routes, intercepting routes, rewrites, redirects, or middleware.
• React Server Components, server actions, page components, or layouts.
• Runtime Next.js configuration evaluation.
• Changes to the TypeScript/JavaScript extractors or graph core.

Contributor references

• Extending the code graph
• src/graph/resolution/frameworks/express.ts
• src/graph/__tests__/resolver-express.test.ts

Contributor workflow

git switch code-graph-preview
git pull
git switch -c feat/nextjs-app-router-resolver

Open the pull request with base branch code-graph-preview.

[abhinav-phi]

Hi @theDakshJaitly,

I'd like to work on this issue. If it's still available, could you please assign it to me?

Thanks!