matimo: Skill for Claude Code

Turn a messy working tree (many modified/untracked files spanning several unrelated efforts) into a small number of clean, reviewable commits — each one a single concern — without dragging in excluded topics or unrelated noise.

Hard rule — read this before staging anything

git commit -- <pathspec> does NOT commit the index for those paths. It silently re-stages the full current working-tree content of every matching path first, then commits that.

This means: if you carefully split a file into "wanted hunk" (staged) + "unwanted hunk" (left unstaged) via git apply --cached <patch>, and then run git commit -m "..." -- path/to/that/file, git throws away your careful staging and commits the entire working-tree diff for that file — wanted and unwanted hunks both. This fails silently: the commit succeeds, looks reasonable in the summary, and the pollution only shows up if you diff the commit against what you intended.

Consequence: once ANY file in the commit needs partial-hunk staging (some lines committed now, some left for later/never), you cannot scope that commit with a trailing pathspec. Instead:

1. Build the index to contain exactly the target commit's content — nothing more, nothing less:
   • Whole files: git add <path>
   • Partial files: git apply --cached <hunk-patch> (see "Splitting a single file" below) — never git add <path> on a file you're only partially staging.
2. Check for pre-existing staged content that predates this task (e.g. the user had files already staged before you started — git status shows these with a non-space index column). Unstage anything not part of the current commit with git reset -- <path> (this only touches the index, never the working tree).
3. Verify the index is exactly right: git diff --cached --stat for the whole set, and git diff --cached -- <file> + git diff -- <file> for any partially-staged file (staged half should be the wanted hunk; unstaged remainder should be everything else).
4. Commit with no trailing pathspec: git commit -m "...". The index is already correct — trust it.
5. After every commit, sanity-check it actually contains what you think: git show <sha> --stat and, for any file you partial-staged, git show <sha> -- <file> to eyeball the hunks.

If you skip step 5 and only discover the leak later, see "Recovering from a polluted commit" below — it's fixable without amending.