Clear when the unit is done, not when the session feels long

Start a new context every time you finish a unit of work, even when the next thing is related. Especially then, because “related” is what talks you into keeping the session open.

I have already written that the cost compounds: the whole conversation gets re-read every turn, so the total grows with the square of the message count. What I left sitting in its own section, and should not have, is the cache. A cached read costs roughly a tenth of a full one, which feels like the compounding got solved. It did not. A tenth of a number that keeps growing is a number that keeps growing. The discount buys a slower climb, never a flat line.

So the session stopped being my unit and the finished piece of work became it. Migration done, clear. Bug reproduced and fixed, clear. The next task inherits the files, which is where the work actually lives, and it has no use for the transcript of how the last one got there.

The version of this rule I hear most often is time based: step away for longer than the cache lives and you pay full price to rebuild it, so clear before the break. True, and the wrong trigger. It only fires when you happen to leave the desk. Finishing something happens far more often than that.