Tune the Harness to the Model

Wrenfold changed models on a Monday. The new one was better at everything the team could measure independently: it planned further ahead, held a longer task in mind, and wrote cleaner patches on the first attempt.

The loop got worse. Cost per verified feature rose by a third, and two of twelve CLIN-547 runs ended in STOP_NO_PROGRESS on failures the previous model had cleared.

The cause was in the harness, and it had been correct when it was written. The loop forced a full session reset every forty minutes, because the earlier model started wrapping up prematurely as it approached what it believed was its context limit. The new model sustained a long task comfortably. The reset now interrupted productive work eight times a day and paid the cold-start cost each time.

The second cause was the action unit. The Scope Contract allowed one narrow repair hypothesis per attempt, which had been the fix for a model that drifted whenever given room. The new model could plan a coherent three-file change and was now forced to deliver it in pieces, re-establishing context between each one.

Nothing in the harness had broken. The assumptions inside it had expired.

Why did a better model make the harness worse?

Because every control was built to compensate for something, and nobody wrote down what.

A forced context reset is not a general good. It is a specific answer to a specific deficiency. So is a planner that expands a thin ticket, a narrow action unit, a re-read of the contract at every attempt, and an instruction that allows only one feature per attempt. Each was added because a model failed without it.

When the deficiency goes away, the compensation stays, and compensation with nothing left to compensate for is pure cost. Worse than cost: the reset and the narrow action unit actively fought a model that no longer needed either.

This is the reliability side of the course’s line turned on the ...