A long answer no longer costs the portal more than it says

When an agent writes you a reply, the text appears a few words at a time. Behind that, roughly ten times a second, the portal saved the answer so far so that the page you are watching — and anyone else watching the same conversation — stays up to date.

The problem was what it saved. Every one of those saves carried the whole answer from the beginning, not just the words that had arrived since the last one. Early in a reply that costs nothing. By the end of a long one it means shipping the entire text again, and again, and again. A page-length answer ended up moving several megabytes through the portal to deliver twenty kilobytes of writing — and the cost grew with the square of the answer's length, so an answer twice as long was four times as expensive.

Nobody saw a wrong word on screen; the text was always correct. What people saw was everything else getting slower while a long reply was in progress. Handling those repeated copies is real work for the machine, and it competes with every other thing the portal is doing at that moment — other people's pages, background jobs, the health checks that decide whether the service is answering at all.

Now a save carries only the part that changed. The portal already has the earlier text; it does not need to be told again. In a measured run, a twenty-thousand-character answer went from 3.8 MB of saved updates to 0.07 MB — about fifty-five times less — and the cost now grows in step with the answer's length instead of racing ahead of it.

Two things are deliberately unchanged. The finished text is identical to the character — this is a change in how the update travels, never in what it says. And if two things somehow write to the same text at the same moment, the portal refuses the second one and has it start again from the current text rather than guessing where the new words belong; correctness wins over saving a round trip.

The same saving applies anywhere the portal stores a large piece of text that grows or is edited in place — long documents, generated pages, notes — not just agent replies.