Describe the bug

When using a custom rollup plugin that replaces special module identifiers with out-of-band content generated on the basis of that identifier (e.g., import foo from 'special-loader:./module';, where special-loader:./module has a custom Rollup plugin that uses load() to runs a special build on the basis of ./module), Vite will never call the load() method of the plugin for that module again until the dev server is restarted, even if you use this.addWatchFiles() in the plugin to list files as out-of-band dependencies.

Reproduction

https://github.com/lemonmade/vite-example — README has instructions, but the basic gist is to run yarn && yarn dev, then edit worker.js, and note that the updates are never triggered in the actual built file.

System Info

Output of npx envinfo --system --npmPackages vite,@vitejs/plugin-vue --binaries --browsers:

  System:
    OS: macOS 11.3.1
    CPU: (8) arm64 Apple M1
    Memory: 2.27 GB / 16.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 15.4.0 - ~/.nvm/versions/node/v15.4.0/bin/node
    Yarn: 1.22.10 - ~/.nvm/versions/node/v15.4.0/bin/yarn
    npm: 7.0.15 - ~/.nvm/versions/node/v15.4.0/bin/npm
  Browsers:
    Chrome: 90.0.4430.212
    Firefox Developer Edition: 87.0
    Safari: 14.1
    Safari Technology Preview: 14.2
  npmPackages:
    vite: ^2.3.3 => 2.3.3 

Used package manager: yarn

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