The problem I kept hitting: git diff shows what changed, but not why the agent changed it, what outcome it expected, what check it planned to run, or how to roll back one specific action. Final summaries are often too coarse, especially after a long coding session.

Ponytrail adds a small local trail around file mutations. Before an agent creates, edits, moves, deletes, formats, or generates files, it records a pre-change snapshot: action, purpose, reason, files, expected outcome, verification plan, rollback path

After the edit, it records a post-change snapshot with what changed, what checks ran, and the result.

Everything is stored locally under .pony-trail/ as JSONL, session trees, and small before/after file copies. It does not replace git. It is more like per-action intent and rollback context for agent work.