Issue Summary

Users are unable to connect a new Slack workspace to a Jira site if there are already workspaces configured and approved in the Global Slack Integration settings. When attempting to connect a new workspace via Space Settings > Slack Integration, the OAuth "Allow" handshake completes, but the workspace fails to appear in Jira and the connection is not established.

This creates a "Catch-22" scenario:

1. A workspace must be approved in the Global Settings before it can connect.
2. A workspace does not appear in the Global Settings "Manage Workspaces" list for approval until it has an active connection or notification relationship.

Steps to Reproduce

1. Navigate to Jira Settings > Apps > Slack Integration > Global Settings.
2. Ensure at least one workspace is already connected and approved.
3. Navigate to any Space Settings > Slack Integration.
4. Attempt to connect a new Slack workspace that has never been linked to this site before.
5. Complete the Slack "Allow" authorization.

Expected Results

The workspace should appear in the "Needs Review" section of the Global Settings or be available for selection in the Space Settings.

Actual Results

The authorization page closes, but the workspace is not registered in Jira. Internal logs may show: Add-on 'jira-slack-integration' disallowed to impersonate the user because 'no valid active user exists'.

Workaround

1. Navigate to the Global Slack configuration page: https://<site-name>.atlassian.net/plugins/servlet/ac/jira-slack-integration/addon-config-page.
2. Click Manage workspace.
3. Temporarily remove all selected workspaces from the "Select to approve workspaces" dropdown and click Confirm. (This moves all workspaces to a "Needs Review" state).
4. Go back to Space Settings > Slack Integration and attempt to connect the new workspace again.
5. Once connected, create a temporary channel subscription.
6. Return to the Global configuration page and re-approve all workspaces (including the new one) in the Manage workspace modal.