The package and publish steps could be added to package.json and also then to a workflow for a release. For now, manually using and also uploading to a release will work. The trick is to do the build after using tagging (e.g. npm version minor), to ensure the name of the filename and the contents matches.

$ vsce package
Executing prepublish script 'npm run vscode:prepublish'...
...
DONE  Packaged: /home/michael/repos/auto-commit-msg/auto-commit-msg-0.6.0.vsix (31 files, 33.21KB)

Alternatively specify ignored build directory. Some may prefer dist for distribution.

$ vsce package --out build

Example output name: auto-commit-msg-0.6.0.vsix. That will be in the repo root or a given out directory.

$ vsce package -h

Usage: package [options]

Packages an extension

Options:
  -o, --out [path]        Output .vsix extension file to [path] location
  --baseContentUrl [url]  Prepend all relative links in README.md with this url.
  --baseImagesUrl [url]   Prepend all relative image links in README.md with this url.
  --yarn                  Use yarn instead of npm
  --ignoreFile [path]     Indicate alternative .vscodeignore
  --noGitHubIssueLinking  Prevent automatic expansion of GitHub-style issue syntax into links
  -h, --help              output usage information