## Problem
In a TypeScript monorepo using nx, running `mastra dev` failed to resolve imports that used custom `paths` aliases from the root tsconfig.json (for example `@my-project/constants` pointing at `libs/constants/src/index.ts`), even though the paths worked fine everywhere else in the project. Importing workspace packages also failed with `TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts"`. A direct `tsx ./src/main.ts` run worked, but that blocked use of the Mastra Playground.
## Verified fix
This was fixed by the Mastra team adding tsconfig paths support to the dev server. Verified resolution: upgrade to mastra 0.4.3-alpha.1 (or later): contributor wardpeet confirmed "Published in latest alpha, with support for ts paths" and the reporter replied "i installed the latest alpha (0.4.3-alpha.1) and this worked for me. thank you!". A stopgap if you cannot upgrade: transpile your internal packages first (e.g. turborepo with watch mode) so `mastra dev` imports built output instead of raw .ts. Source: https://github.com/mastra-ai/mastra/issues/1996