When a session ends, the answer survives but the how evaporates. Three wrong turns, the real root cause, the rule that would prevent the whole class of problem, all gone. This skill installs a recorder: after any non trivial solve, capture the symptom, root cause, fix, and the one line rule as a short learnings note.
The test for whether a note is worth writing: would a future session, or a less capable model, save time by reading it? The value is not the answer, which can be re derived. It is the distilled judgment that took real effort to reach. The silent Gradle failure post on this log started life as exactly this kind of note.
The habit compounds. Notes accumulate per project, every future session reads them instead of relearning them, and one off solves become permanent assets. The cheapest infrastructure I own.