The login bug is fixed. Now you want a checkout page. Start a new session.
Long chats collect old requirements, failed experiments, and decisions you already reversed. The agent has more history to sort through, and its context window is finite. More conversation does not automatically mean better context.
Start fresh when the previous task is done, the direction changes substantially, or you keep correcting old assumptions. Keep replying when you are still solving the same problem.
You do not need to explain everything again. Ask the agent to prepare a short handoff: the current goal, decisions, relevant files, completed work, test results, and what remains.
If the app gives the agent tools to create chats, you can ask it to make the move:
Start a new chat in this project for the checkout page. Carry over the decisions, relevant files, completed work, test results, known problems, and next steps. Return a link to the new chat.
If it cannot create chats, ask for that handoff and paste it into a new one yourself.
Check that a separate chat appears in the sidebar and that its opening brief contains what you need. Saying "start fresh" inside the old conversation does not, by itself, create a new session.