A browser sends a request with a method, target, headers, and sometimes cookies. The server returns a status, headers, and content. Authentication identifies a user; authorization must still check access to each order.
SSE sends text/event-stream over ordinary HTTP, with browser reconnection and Last-Event-ID; simple transport is not durable unless the server retains events behind that cursor.
An agent should not open a browser for every web task: route first to Search or Fetch, then escalate on explicit signals such as status codes, weak content, JavaScript shells, authentication, or challenge pages, with retry, budget, cache, deduplication, and provenance constraints at every step.