Feature request: subscribe or unsubscribe to a specific issue, PR, or discussion #3452

Describe the feature or problem you'd like to solve

There is no tool to subscribe to notifications for one specific issue, pull request, or discussion, the way the "Subscribe" button in the issue sidebar does.

• manage_notification_subscription only works on an existing notification thread.
• manage_repository_notification_subscription watches the whole repository, which is far too broad.
• So agents are left either commenting (noisy for maintainers) or driving a browser.

Proposed solution

Add a tool such as manage_issue_subscription that takes owner, repo, and an issue, PR, or discussion number, plus a state of subscribed, unsubscribed, or ignored. The GraphQL API already supports this through the updateSubscription mutation and viewerSubscription.

Example prompts or workflows (for tools/toolsets only)

1. "Subscribe me to owner/repo#<number> so I hear when it's fixed."
2. "Find the upstream issue for this bug and subscribe me instead of leaving a +1 comment."
3. "Unsubscribe me from closed issues I'm still getting notifications for in repo X."
4. "Am I subscribed to this PR? If not, subscribe me."

Additional context

An AI agent using the GitHub MCP server found the upstream feature request I cared about but had no way to subscribe me, so it had to sign in to a browser and click the button.