The use case you're trying to solve

Production deploy doesn't set details_url output, but prints it in the action when run

Change to the action that would solve that use case

ensure that for production deployment code the following is set as say line 101 in file https://github.com/FirebaseExtended/action-hosting-deploy/blob/0f248036885ae672f78587669fa2923f0ef6cac2/src/index.ts

setOutput("details_url",url);

Other considerations

Although the url for production is known and static, for the purposes of using a github action, if the wiki says the output is available it should be, the Readme at https://github.com/FirebaseExtended/action-hosting-deploy#outputs should also be updated to reflect the following

urls
The url(s) deployed to (preview channels only)

expire_time
The time the deployed preview urls expire (preview channels only)

details_url
A single URL that was deployed to (production & preview)