Error text: `(ResourceGroupNotFound) Resource group '[name]' could not be found.`
Checklist, in order:
1. `az account show --query "{sub:name, id:id}"` - is this the subscription the group lives in? If not, `az account set --subscription [id]`. This is the cause most of the time.
2. `az group list --query "[].name"` - does the group exist in this subscription at all? Watch for typos: names are case-insensitive in Azure but your script's string must still match.
3. `az group show -n [name]` - if list shows it but show fails, you have a read-permission gap (Reader on the subscription but the group listing came from cache, or a deny assignment).
4. Activity log: `az monitor activity-log list --resource-group [name]` - if the group existed and is gone, the log shows who deleted it and when. Groups deleted in the last 14 days are visible here.
5. If a deployment just created it: ARM is eventually consistent. A `get` immediately after `create` in a different process can 404 for a few seconds. Retry with backoff before concluding failure.
Automation rule: every script that takes a resource-group parameter should `az group show` (or the SDK equivalent) as its first step and fail fast with the subscription id in the message. The error is cheap to check and expensive to debug downstream.