nestjs/nest

This brief is bounded to the inspected tracked sources at the pinned commit. Tests and CI were inspected, not executed, and no runtime or performance result is claimed. Start changes at the owning package and follow its public contract into a representative integration fixture. Preserve ESM import conventions, decorator metadata, adapter behavior, and existing test configuration; treat sample settings and coverage output cautiously.

• Read root scripts and the owning package manifest first: root version is 12.0.0, while inspected common/core manifests and Lerna use 12.1.2.
  package.json#L1-3packages/common/package.json#L1-3packages/core/package.json#L1-3lerna.json#L1-4
• Preserve .js relative import suffixes in TypeScript and the Node16 resolution/decorator settings.
  packages/core/nest-factory.ts#L10-25tsconfig.json#L2-17
• For startup edits, read NestFactory.initialize, DependenciesScanner.scan, InstanceLoader, and NestApplication.init before changing ordering.
  packages/core/nest-factory.ts#L212-252packages/core/scanner.ts#L84-102packages/core/injector/instance-loader.ts#L25-59packages/core/nest-application.ts#L188-210
• For adapter work, inspect the AbstractHttpAdapter contract and native stream behavior; the interface documents request and Node-server assumptions.
  packages/core/adapters/http-adapter.ts#L16-47packages/platform-express/adapters/express-adapter.ts#L120-142
• For later authorized verification, npm test selects package unit specs directly from source; contributor documentation states these need neither a build nor Docker.
  package.json#L35-38vitest.config.mts#L47-62CONTRIBUTING.md#L169-176
• Integration preparation builds framework packages into node_modules/@nestjs and starts Docker services; inspect that environment requirement before running integration commands.
  CONTRIBUTING.md#L178-187package.json#L38-41
• Tests and CI in this report were inspected only; configured commands and assertions are evidence of intended checks, not executed passing results.
  package.json#L35-38.circleci/config.yml#L31-34integration/hello-world/e2e/hello-world.spec.ts#L43-74
• Do not use coverage scripts as failure gates without accounting for || true and central runtime exclusions.
  package.json#L32-38vitest.config.coverage.mts#L67-88
• Use TestingModuleBuilder overrides and repository-token mocks to isolate application services; the SQL sample demonstrates this pattern.
  packages/testing/testing-module.builder.ts#L91-101sample/05-sql-typeorm/src/users/users.service.spec.ts#L27-45
• Keep compatibility handling in assignMetadata when editing parameter decorators; it explicitly supports callers using the pre-v12 positional signature.
  packages/common/decorators/http/route-params.decorator.ts#L48-68
• Route diagnostics must run before duplicate-rejecting adapter registration; specificity sorting also affects which route is reported as the winner.
  packages/core/nest-application.ts#L251-269