Add a plugin or connect it [write]

Runs the source's own add: tool:<id> is switched on in the workspace's default environment; skill:<id> attaches to every new session; bundle:<name> is switched back on, or installed from source or the marketplace that lists it; app:<slug> starts connecting (success_url/error_url default to the consumer app's own callback) and answers next.url, the address the person opens to sign in; with task_id and request_id instead, next.url is the once-only connect link of that task's connect_app request, as POST /connectors/links (404 when the task has no such open request, 403 request_not_yours, 422 wrong_app when it asks for another app); chat:<platform> starts the chat-app connect (agent_id or session_id chooses who answers, app a registered app) and answers the pairing page as next.url; mac:<id> and browser:<scope> answer next.steps, and mac:meetings with agent_id adds its follow-up routine for that agent, paused (one already there is left as it is). A merged product's first id connects its app and names its chat app's pairing in next.steps; a bundle names one app per category it still needs. When a person must finish, the answer is 202 with status needs_you; otherwise 200 added. 403 plugin_blocked when an admin blocked it; 403 person_required for apps and chat apps under a workspace key. A custom MCP server is added with POST /plugins {mcp_url}.