Cloudflare pages cannot import modules from non-existent files

I have a small server made with Hono.js, and on its last deployment, I got this cryptic error:

Error: Failed to publish your Function. Got error: Uncaught Error: Can't import modules from ['/src/index.tsx','/app/server.ts']
  at functionsWorker-0.33606875306880757.js:958:9

We don’t have a frontend, a /app directory or an index.tsx file anywhere in our project, so I don’t know why Cloudflare is expecting them. What’s going on here?

Server source code here: