fixup

Fixup Commit

Announce: "I'm using the fixup skill to match current changes to an existing branch commit."

Fixup creates a commit that will be squashed into a target commit during the next interactive rebase with --autosquash. This skill identifies the right target automatically.

Step 1: Inventory Changes and Branch History

Run in parallel:

git status            # never use -uall
git diff --staged --name-only
git diff --name-only
git ls-files --others --exclude-standard
git branch --show-current

If no staged and no unstaged and no untracked changes: inform the user there is nothing to fixup and stop.

Determine the merge base:

git merge-base HEAD main 2>/dev/null || git merge-base HEAD master 2>/dev/null || git rev-list --max-parents=0 HEAD

If the current branch IS main/master: inform the user that fixup targets feature branch commits and stop.

Get all commits on the branch since the merge base:

git log --oneline --reverse <merge-base>..HEAD

If no commits ahead of base: inform the user there are no commits to fixup and stop.

For each commit, collect its touched files:

git diff-tree --no-commit-id --name-only -r <sha>

Step 2: Identify Changed Files

Determine the change set — the files to match against branch commits:

Condition	Change set
Staged files exist	Staged files only
No staged files	All modified + untracked files

If nothing remains: inform the user and stop.

Step 3: Match Changes to a Commit

If $ARGUMENTS contains a commit hash or unambiguous description: resolve it to a SHA and skip to Step 4. Verify the SHA is within the branch range (<merge-base>..HEAD).

Single-commit fast path: If there is exactly one commit on the branch, it is the target. Confirm with the user and skip to Step 4:

AskUserQuestion( header: "Target commit", question: "Only one commit on this branch: (). Fixup into it?", options: [ "Yes" -- Create fixup targeting that commit, "No, new commit" -- Create a regular commit instead via /commit ] )

For each branch commit, compute a file overlap score:

1. Direct overlap: count of files that appear in both the change set and the commit's touched files.
2. Directory overlap: count of change set files whose parent directory contains at least one file from the commit (but the file itself was not touched by that commit).

Rank commits by direct overlap first, then directory overlap as tiebreaker.

Decision logic:

Situation	Action
One commit has the highest direct overlap (> 0)	Use that commit
Multiple commits tied on direct overlap	Show candidates, ask user to choose
No commit has any direct overlap	Go to Step 3b

Step 3b: Semantic Matching (No File Overlap)

When no commit shares files with the change set, check for logical relationships:

1. Read the change set diffs (git diff --staged or git diff + untracked file contents).
2. Read each branch commit's message and diff summary (git log -1 --stat <sha>).
3. Look for: new test files for code introduced in a commit, new files imported by files in a commit, documentation for a feature added in a commit.

If a logical match is found: present it to the user with the reasoning and ask for confirmation.

If no match is found: inform the user:

None of the N commits on this branch appear related to the current changes.

Branch commits:
  abc1234 Add user authentication
  def5678 Refactor database layer

Changed files:
  src/logging/formatter.ts
  src/logging/levels.ts

Consider creating a new commit instead (/commit).

Stop.

Step 4: Stage and Create Fixup Commit

If nothing is staged, stage the change set files:

git add <file1> <file2> ...

Create the fixup commit:

git commit --fixup=<target-sha>

Report the result:

Created fixup commit <new-sha> targeting <target-sha> (<target-message>).

To squash: git rebase -i --autosquash <merge-base>

Error Handling

Error	Action
No changes to fixup	Inform the user and stop
No commits ahead of base branch	Inform the user fixup requires branch commits. Stop.
On main/master branch	Inform the user fixup targets feature branch commits. Stop.
Argument SHA not in branch range	Inform the user the commit is not on this branch. Stop.
No matching commit found	List branch commits and changed files. Suggest /commit instead. Stop.
Commit hook failure	Report the error. Do NOT retry with --no-verify. Let the user decide.
Excluded files staged	Unstage with git reset HEAD <file> before committing