throughline - Consolidate (promotion)

Goal: Handoff distills one session; onboard reads it back. Neither notices that the same lesson has now appeared in four different session logs. This skill is the periodic pass that does: mine the logs since the last pass, find what recurs, and propose promoting it - with a human gate - into the durable layer where it stops needing to be re-learned.

Data directory (resolve once): $THROUGHLINE_DATA_DIR if set, else <project-root>/.claude/throughline/. Below, DATA refers to that path. In a linked git worktree, <project-root> here is the main working tree, not the worktree itself (see README "Git worktrees") - so DATA is shared across every worktree of the repo.