Here is some context about CI:

• the Docker images have the environment variables:
  • XDG_CACHE_HOME=/cache , that is a bind mount from the host and anything in that path ends up being saved in the central cache (nicknamed Castor)
  • XDG_CONFIG_HOME=/tmp/xdg-config-home
• containers run as user nobody which has the home directory set to the directory /nonexistent which is intentionally not existent

At a quick glance, Cypress invokes return cachedir('Cypress') which is cachedir which does:

const cacheHome = process.env.XDG_CACHE_HOME || path.join(os.homedir(), '.cache')

The binary should thus be somewhere under /cache/Cypress. Some possibilities to assist debug is to hack your npm script to add:

• finding the path find /cache -type f -name Cypress || : : will show the file if it exists
• use DEBUG=cypress:cli which enables its debug log and would output something such as:

cypress:cli checking if executable exists /cache/Cypress/13.6.1/Cypress/Cypress +2ms
cypress:cli Binary is executable? : true +2ms
cypress:cli binaryDir is  /cache/Cypress/13.6.1/Cypress +0ms
cypress:cli Reading binary package.json from: /cache/Cypress/13.6.1/Cypress/resources/app/package.json +0ms
cypress:cli Found binary version 13.6.1 installed in: /cache/Cypress/13.6.1/Cypress +4ms
cypress:cli { verified: true } +5ms
cypress:cli is Verified ? true +2ms

Maybe Cypress uses XDG_CONFIG_HOME which is under /tmp and indeed is not saved/restored.

Change #1016618 had a related patch set uploaded (by Hashar; author: Hashar):

[mediawiki/extensions/Cite@master] [DO NOT SUBMIT] Cypress with debugging

https://gerrit.wikimedia.org/r/1016618

Tried it with find / -type f -name Cypress || : and that yields nothing. Thus essentially npm ci does not install the Cypress binary blob. Cypress thus fails later when searching it:

checking if executable exists /cache/Cypress/13.6.1/Cypress/Cypress
The cypress npm package is installed, but the Cypress binary is missing.

Who knows? That is a mystery, I don't know anything about Cypress or why it would not install the binary.

Change #1016618 abandoned by Hashar:

[mediawiki/extensions/Cite@master] [DO NOT SUBMIT] Cypress with debugging

Reason:

https://gerrit.wikimedia.org/r/1016618