Main idea

A skill in eight phases is not eight independent calls. What phase 3 wrote stays in the conversation and is reread at every later phase — not once, but as many times as there are turns left.

That accumulation commonly represents fifteen to forty percent of the real cost, and it shows up on no line of the step-by-step count: it is the main source of the gap between the sum of the steps and the spending observed. Two consequences follow. A step's cost depends on its position in the chain. And reading five files in a single turn rather than in five successive turns removes four layers of carry-over.

Why it matters

This explains why a long skill costs more than the sum of its parts, and why lengthening a workflow by one seemingly harmless step is never harmless.

It also gives a lever nobody looks for spontaneously: grouping independent reads doesn't only speed things up, it unloads the context.

Nuances and limits

It is the most fragile quantity in an audit: it isn't measured, it is estimated from the previous outputs.

And that carry-over is sometimes exactly what you want: a synthesis phase leans on what the earlier phases produced, and isolating it would amount to giving it the same material another way.

Open questions

• How do you interrupt the accumulation between two phases without depriving the next one of what it needs to know?