Git Squash Skill

Purpose: Safely squash multiple commits into one with automatic backup, verification, and cleanup.

Parallel Initial Investigation

OPTIMIZATION: Run initial git commands in parallel to reduce round-trips.

Before starting any squash workflow, gather information concurrently:

# Run these commands in parallel (use & and wait)
git rev-parse HEAD &
git status --porcelain &
git log --oneline <base>..HEAD &
git diff --stat <base>..HEAD &
wait

# All results now available for workflow selection

This reduces the initial investigation from 4+ sequential commands to a single parallel batch.

Safety Pattern: Backup-Verify-Cleanup

ALWAYS follow this pattern:

1. Create timestamped backup branch
2. Execute the squash
3. Verify immediately - no changes lost or added
4. Cleanup backup only after verification passes

Read PROJECT.md Squash Policy

Check PROJECT.md for configured squash preferences before proceeding.

# Read squash policy from PROJECT.md
SQUASH_POLICY=$(grep -A10 "### Squash Policy" .claude/cat/PROJECT.md 2>/dev/null | grep "Strategy:" | sed 's/.*Strategy:\s*//' | head -1)

if [[ "$SQUASH_POLICY" == *"keep all"* || "$SQUASH_POLICY" == *"Keep all"* || "$SQUASH_POLICY" == *"keep-all"* ]]; then
  echo "⚠️ PROJECT.md configured for 'Keep all commits'"
  echo "Squashing will override this preference."
  echo ""
  echo "Options:"
  echo "  1. Proceed with squash (override PROJECT.md preference)"
  echo "  2. Cancel to preserve commits as configured"
  echo ""
  echo "To proceed, continue with this skill."
  echo "To honor PROJECT.md preference, abort the squash operation."
fi

if [[ "$SQUASH_POLICY" == *"single"* || "$SQUASH_POLICY" == *"Single"* ]]; then
  echo "📋 PROJECT.md configured for 'Single commit' squashing"
  echo "All commits will be squashed into one (not by type)."
fi

if [[ "$SQUASH_POLICY" == *"by-type"* || "$SQUASH_POLICY" == *"by type"* ]]; then
  echo "📋 PROJECT.md configured for 'Squash by type'"
  echo "Commits will be grouped by type prefix."
fi

Workflow Selection

CRITICAL: Choose workflow based on commit position.

# Check if commits are at tip of branch
LAST_COMMIT="<last-commit-to-squash>"
BRANCH_TIP=$(git rev-parse HEAD)

if [ "$(git rev-parse $LAST_COMMIT)" = "$BRANCH_TIP" ]; then
    echo "Commits at tip → Use Quick Workflow (soft reset)"
else
    echo "Commits in middle of history → Use Interactive Rebase Workflow"
fi

Planning Commit Pattern Detection

Detect common "feature + planning STATE.md update" pattern.

Before squashing, check if the commit sequence follows this pattern:

1. Implementation commit(s): feature:, bugfix:, refactor:, etc.
2. Final commit(s): planning: or config: with only .claude/cat/issues/ changes

Detection logic:

# Get the last commit's type and files
LAST_COMMIT=$(git log -1 --format="%s" HEAD)
LAST_FILES=$(git diff-tree --no-commit-id --name-only -r HEAD)

# Check if last commit is planning-only
if [[ "$LAST_COMMIT" =~ ^planning: ]] && \
   [[ "$LAST_FILES" =~ \.claude/cat/issues/ ]] && \
   ! echo "$LAST_FILES" | grep -qv "\.claude/cat/"; then
    echo "PATTERN DETECTED: Final commit is planning-only STATE.md update"
    # This pattern indicates STATE.md should be preserved in squash
fi

When pattern detected:

• Extract final STATE.md content before squash
• After squash, ensure STATE.md reflects final state (not intermediate)
• Include planning changes in implementation commit per M076

Quick Workflow (Commits at Branch Tip Only)

Use ONLY when squashing the most recent commits on a branch.

# 1. Verify commits are at tip
git log --oneline -1  # Should show <last-commit-to-squash>

# 2. Create backup
BACKUP="backup-before-squash-$(date +%Y%m%d-%H%M%S)"
git branch "$BACKUP"

# 3. Verify clean working directory
git status --porcelain  # Must be empty

# 4. Check for unintended deletions (M238)
# If base branch has files your branch doesn't, soft reset will stage deletions!
echo "Files on base but not in branch (will be DELETED if you proceed):"
git diff --name-status <base-commit>..HEAD | grep "^D" | cut -f2
# If any unexpected files shown, sync with base first:
#   git checkout <base-commit> -- <path-to-restore>

# 5. Soft reset to base (parent of first commit to squash)
git reset --soft <base-commit>

# 6. Verify no UNINTENDED changes (check for unexpected deletions!)
git diff --stat "$BACKUP"  # Must be empty
git diff --name-status HEAD | grep "^D"  # Review any deletions!

# 7. Create squashed commit (see git-commit skill for message guidance)
git commit -m "Unified message describing what code does"

# 8. Verify result
git diff "$BACKUP"  # Must be empty
git rev-list --count <base-commit>..HEAD  # Must be 1

# 9. Cleanup backup
git branch -D "$BACKUP"

Interactive Rebase Workflow (Commits in Middle of History)

Use when commits to squash have other commits after them.

# 1. Create backup of current branch
BACKUP="backup-before-squash-$(date +%Y%m%d-%H%M%S)"
git branch "$BACKUP"

# 2. Create sequence editor script
FIRST_COMMIT="<first-commit-to-squash>"  # Keep this one, squash others into it
COMMITS_TO_SQUASH="<second-commit> <third-commit> ..."  # These get squashed

cat > /tmp/squash-editor.sh << EOF
#!/bin/bash
$(for c in $COMMITS_TO_SQUASH; do echo "sed -i 's/^pick $c/squash $c/' \"\$1\""; done)
EOF
chmod +x /tmp/squash-editor.sh

# 3. Create commit message editor script
cat > /tmp/msg-editor.sh << 'EOF'
#!/bin/bash
cat > "$1" << 'MSG'
<your unified commit message here>
MSG
EOF
chmod +x /tmp/msg-editor.sh

# 4. Run interactive rebase
# NOTE: Use GIT_EDITOR (not EDITOR) - git uses GIT_EDITOR for commit messages during rebase
BASE_COMMIT="<parent-of-first-commit>"
GIT_SEQUENCE_EDITOR=/tmp/squash-editor.sh GIT_EDITOR=/tmp/msg-editor.sh git rebase -i $BASE_COMMIT

# 5. Verify no changes lost
git diff "$BACKUP"  # Must be empty

# 6. Cleanup
git branch -D "$BACKUP"
rm /tmp/squash-editor.sh /tmp/msg-editor.sh

Critical Rules

Check for Unintended Deletions (M238)

CRITICAL: Worktrees may be out of sync with base branch updates.

When using git reset --soft <base>, the index reflects your working tree state. If the base branch has files your branch never received (e.g., new files added to base after your branch diverged), the soft reset will stage those files as DELETIONS.

Before committing after soft reset:

# Check what will be deleted relative to base
git diff --name-status HEAD | grep "^D"

# If unexpected deletions appear, restore from base:
git checkout <base> -- <path-to-unexpected-deleted-file>

# Then amend the commit
git commit --amend --no-edit

Why this happens:

1. Branch created from older base commit
2. New files added to base branch later
3. Worktree never received these files (no merge/rebase from base)
4. Soft reset stages "delete files that exist on base but not in working tree"

Preserve Commit Type Boundaries When Squashing

CRITICAL: Follow commit grouping rules from commit-types.md.

Key rules when squashing:

• Task STATE.md → same commit as implementation (M076)
• Different commit types (feature: vs docs:) → keep separate
• Related same-type commits → can combine

Before squashing, analyze commit types:

# List commits with their types
git log --oneline <base>..HEAD | while read hash msg; do
    type=$(echo "$msg" | cut -d: -f1)
    echo "$type: $hash ${msg#*: }"
done | sort -t: -k1

# Group by type to determine squash strategy
git log --format="%s" <base>..HEAD | cut -d: -f1 | sort | uniq -c

Automatic STATE.md Preservation

CRITICAL: Preserve final STATE.md state when squashing planning commits.

When squashing commits that include STATE.md updates:

1. Before squash: Record the final STATE.md content

   # Store final state before squash
   TASK_STATE=".claude/cat/issues/v*/v*.*/*/STATE.md"
   git show HEAD:$TASK_STATE > /tmp/final-state.md 2>/dev/null || true
   

2. After squash: Verify STATE.md wasn't reverted to intermediate state

   # Check if STATE.md was affected
   if [[ -f /tmp/final-state.md ]]; then
       # Compare current vs final
       if ! diff -q "$TASK_STATE" /tmp/final-state.md >/dev/null 2>&1; then
           echo "⚠️ STATE.md reverted to intermediate state - restoring final state"
           cp /tmp/final-state.md "$TASK_STATE"
           git add "$TASK_STATE"
           git commit --amend --no-edit
       fi
   fi
   

Why this matters:

• Squashing can revert STATE.md to earlier commit's version
• Final state (status: completed, progress: 100%) must be preserved
• Per M076: STATE.md belongs in same commit as implementation

Use Correct Workflow for Commit Position

# WRONG - Using soft reset workflow for mid-history commits
git checkout <mid-history-commit>
git reset --soft <base>
git branch -f main HEAD  # LOSES all commits after the squash range!

# CORRECT - Use interactive rebase for mid-history commits
GIT_SEQUENCE_EDITOR=... git rebase -i <base>  # Preserves all commits

Position HEAD First (Quick Workflow Only)

# WRONG - HEAD beyond squash range
git reset --soft <base>  # Squashes ALL commits to current HEAD!

# CORRECT - Checkout last commit first
git checkout <last-commit>
git reset --soft <base>  # Squashes only intended range

Write Meaningful Commit Messages with Task ID

# WRONG - Concatenated messages, no Task ID
feature(auth): add login
feature(auth): add validation
bugfix(auth): fix typo

# CORRECT - Unified message with Task ID footer
feature: add login form with validation

- Email/password form with client-side validation
- Server-side validation with descriptive messages

Task ID: v1.1-implement-user-auth

MANDATORY: Include Task ID: v{major}.{minor}-{task-name} as the last line.

See git-commit skill for detailed message guidance.

Verify Immediately After Commit

# Check no changes lost
git diff "$BACKUP"  # Empty = success

# Check commit count
git rev-list --count <base>..HEAD  # Should be 1

Squash vs Fixup

Command	Message Behavior	When to Use
squash	Combines all messages	Different features being combined
fixup	Discards secondary messages	Trivial fixes (typos, forgotten files)

When in doubt, use squash - you can edit the combined message.

Non-Adjacent Commits

For commits separated by others, use interactive rebase:

git rebase -i <base-commit>

# In editor: Move commits to be adjacent, mark with 'squash'
# Example:
#   pick abc123 Target commit
#   squash def456 Commit to combine (MOVED here)
#   pick ghi789 Other commit (unchanged)

Conflict Pre-Computation for Non-Adjacent Commits

Before attempting to squash non-adjacent commits, analyze potential conflicts:

# Identify files modified by multiple commits in the range
echo "Conflict risk analysis:"
git diff --name-only <base>..HEAD | while read file; do
    commits=$(git log --oneline <base>..HEAD -- "$file" | wc -l)
    if [[ $commits -gt 1 ]]; then
        echo "  ⚠️ $file: modified by $commits commits"
    fi
done

# Check for same-line modifications (highest risk)
for file in $(git diff --name-only <base>..HEAD); do
    git log -p <base>..HEAD -- "$file" | grep -E "^@@" | sort | uniq -d && \
        echo "  🔴 $file: same lines modified by multiple commits - HIGH RISK"
done

Risk Levels:

Risk	Pattern	Recommendation
LOW	Different files per commit	Safe to squash
MEDIUM	Same file, different lines	Usually safe
HIGH	Same file, same lines	Manual resolution likely needed

Error Recovery

# If anything goes wrong:
git reset --hard $BACKUP

# Or check reflog:
git reflog
git reset --hard HEAD@{N}

Success Criteria

• Backup created before squash
• HEAD positioned at correct last commit
• No changes lost (diff with backup is empty)
• Single commit created with all changes
• Meaningful commit message (not "squashed commits")
• Backup removed after verification