split-commits: Add skill for non-interactive commit splitting

.gitignore

@@ -0,0 +1,2 @@
+__pycache__/
+*.pyc

Justfile

@@ -0,0 +1,15 @@
+# Basic development workflows
+# Run `just --list` to see available targets.
+
+# Python scripts to check
+python_scripts := "diff-quiz/scripts/quiztool perform-forge-review/scripts/reviewtool split-commits/scripts/git-split-commits"
+
+# Run basic syntax checks on all scripts
+check:
+    #!/bin/bash
+    set -euo pipefail
+    echo "Checking Python syntax..."
+    for script in {{python_scripts}}; do
+        python3 -m py_compile "$script" && echo "  ✓ $script"
+    done
+    echo "All checks passed."

README.md

@@ -4,5 +4,6 @@ Skills are defined using the [Agent Skills](https://agentskills.io/) format.
 Each skill is a directory containing a `SKILL.md` file with instructions
 for AI agents.
 
-At the current time, these skills are not intended for use outside
-of the organization.
+This is intentially split into its own git repository to make it
+easier to reuse these skills outside of this organization. However there
+is no explicit commitment to stability.

split-commits/SKILL.md

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+---
+name: split-commits
+description: Split mixed working tree changes into clean, logical commits. Use when you have intermixed changes (features, bugfixes, refactoring) that should be separate commits.
+---
+
+# Split Commits
+
+Non-interactive tool for splitting working tree changes into multiple clean
+commits. Designed for AI agents that don't have TTY access for `git add -i`.
+
+## Problem
+
+When working on code, changes for different concerns (features, bugfixes,
+refactoring) often get intermixed. Creating clean, logical commits requires
+splitting these changes, but the standard tools (`git add -i`, `git add -p`)
+are interactive and require a TTY.
+
+## Prerequisites
+
+- Python 3.10+
+- `jq` (optional, for parsing JSON output)
+
+## Workflow
+
+Use `scripts/git-split-commits` for all operations.
+
+### 1. Identify the topics
+
+Before starting, identify the logical groupings for your changes. Common patterns:
+- `feature`, `bugfix`, `refactor`
+- `api`, `models`, `tests`
+- `feat-X`, `feat-Y`, `cleanup`
+
+### 2. Prepare the session
+
+```bash
+scripts/git-split-commits prepare "bugfix" "refactor" "feature"
+```
+
+Output (JSON):
+```json
+{
+  "status": "prepared",
+  "topics": ["bugfix", "refactor", "feature"],
+  "total_hunks": 6,
+  "files": ["api.py", "models.py", "utils.py"]
+}
+```
+
+### 3. Review hunks
+
+View the session status:
+```bash
+scripts/git-split-commits status
+```
+
+View the next unassigned hunk:
+```bash
+scripts/git-split-commits next
+```
+
+The output includes:
+- `id`: The hunk identifier
+- `file`: Which file this hunk is in
+- `old_start`/`new_start`: Line numbers
+- `first_context`: First context line (for identification)
+- `first_change`: First changed line (shows what's being modified)
+- `patch`: The full unified diff for this hunk
+
+### 4. Assign hunks to topics
+
+```bash
+scripts/git-split-commits assign 0 bugfix
+scripts/git-split-commits assign 1 refactor
+scripts/git-split-commits assign 2 feature
+# ... repeat for all hunks
+```
+
+### 5. Commit in order
+
+Commit topics in logical order (usually: bugfixes first, then refactoring,
+then features):
+
+```bash
+scripts/git-split-commits commit bugfix "fix: Handle edge case in validation"
+scripts/git-split-commits commit refactor "refactor: Rename variables for clarity"
+scripts/git-split-commits commit feature "feat: Add new API endpoint"
+```
+
+### 6. Verify
+
+```bash
+git log --oneline -5
+```
+
+## Key Concepts
+
+### Hunk Identification
+
+Each hunk is identified by:
+- **ID**: A stable numeric identifier within the session
+- **Line numbers**: `old_start` (original) and `new_start` (modified)
+- **Fingerprints**: `first_context` and `first_change` for content verification
+
+### Staleness Detection
+
+The tool validates that files haven't been modified externally:
+- **Blob hash check**: Compares git blob hashes
+- **Line content check**: Verifies context lines still match
+
+If validation fails, you'll need to `reset` and `prepare` again.
+
+### Patch Application
+
+Patches are applied using `git apply --cached`, with `--3way` fallback for
+context conflicts. This handles the case where committing topic A shifts line
+numbers for topic B's patches.
+
+## Commands Reference
+
+| Command | Description |
+|---------|-------------|
+| `prepare TOPIC...` | Initialize session with topic names |
+| `status` | Show all hunks and topic counts (JSON) |
+| `next [ID]` | Show next unassigned hunk, or specific hunk |
+| `assign ID TOPIC` | Assign a hunk to a topic |
+| `stage TOPIC` | Stage all hunks for a topic (without committing) |
+| `commit TOPIC "msg"` | Stage and commit a topic |
+| `reset` | Clear the session |
+
+## Tips for AI Agents
+
+1. **Parse JSON output** for programmatic decisions:
+   ```bash
+   scripts/git-split-commits status | jq '.topic_counts'
+   ```
+
+2. **Use fingerprints** to understand hunks without reading full patches:
+   ```bash
+   scripts/git-split-commits status | jq '.hunks[] | {id, file, first_change}'
+   ```
+
+3. **Commit order matters**: Commit independent changes first, dependent
+   changes last.
+
+4. **When in doubt, refactor first**: Clean code is easier to add features to.
+
+## Example Session
+
+```bash
+# Mixed changes in working tree
+$ git diff --stat
+ src/api.rs   | 25 +++++++++++++++++++------
+ src/utils.rs | 15 +++++++++------
+ 2 files changed, 28 insertions(+), 12 deletions(-)
+
+# Prepare session
+$ scripts/git-split-commits prepare "fix" "feat"
+{"status": "prepared", "topics": ["fix", "feat"], "total_hunks": 3, ...}
+
+# Review and assign
+$ scripts/git-split-commits next | jq '{id, file, first_change}'
+{"id": 0, "file": "src/api.rs", "first_change": "+    // Handle null case"}
+
+$ scripts/git-split-commits assign 0 fix
+$ scripts/git-split-commits assign 1 feat
+$ scripts/git-split-commits assign 2 fix
+
+# Create clean commits
+$ scripts/git-split-commits commit fix "fix: Handle null pointer edge cases"
+$ scripts/git-split-commits commit feat "feat: Add batch processing endpoint"
+
+# Verify
+$ git log --oneline -2
+abc1234 feat: Add batch processing endpoint
+def5678 fix: Handle null pointer edge cases
+```