Just shoving everything into one context fails after just a few turns.
I've had more success with a hierarchy of agents.
A supervisor agent stays focused on the main objective, and it has a plan to reach that objective that's revised after every turn.
The supervisor agent invokes a sub-agent to search and select promising sites, and a separate sub-sub-agent for each site in the search results.
When navigating a site that has many pages or steps, a sub-sub-sub-agent for each page or step can be useful.
The sub-sub-sub-agent has all the context for that page or step, and it returns a very short summary of the content of that page, or the action it took on that step and the result to the sub-sub-agent.
The sub-sub-agents return just the relevant details to their parent, the sub-agent.
That way the supervisor agent can continue for many turns at the top level without exhausting the context window or losing the thread and pursuing its own objective.