Implement version history (git-like undo/redo across sessions)

[espetro]

TL;DR

Add version history that persists across sessions, enabling undo/redo beyond the current session and branching exploration of design variations. Git-like for designers.

User Story

As a user, I want to browse previous versions of my design and restore them, so I can experiment without fear of losing work.

Scope

• Git-like commit model: snapshot project state at meaningful points
• Timeline view: browse history and restore previous states
• Branch/merge: explore variations without losing main thread
• Auto-commit: snapshots before major AI generation
• Commit messages: optional annotations for changes

Tradeoffs / Optionality

Storage Model

Full Snapshots (simpler):

• Pros: Easy to implement, fast restore
• Cons: Storage grows quickly, inefficient

Delta Compression (efficient):

• Pros: Minimal storage, like git
• Cons: Complex implementation, slower restore

Decision: Start with full snapshots. Add delta compression when storage becomes an issue.

Linear vs Branching History

Linear (MVP):

• Pros: Simple UI, easy to understand
• Cons: No parallel experimentation

Branching (P2):

• Pros: True git-like workflow, explore variations
• Cons: Complex UI, merge conflicts

Decision: Linear for MVP. Branching is a P2 enhancement.

Technical Considerations

• Storage: SQLite blob column for snapshots
• Trigger Points:
  • Before AI generation (auto-commit)
  • User explicit save
  • After successful export
• Performance:
  • Serialize canvas state (frames, positions, comments)
  • Compress with zlib or pako
  • Lazy-load history (only load metadata, not full snapshots)
• UI: Timeline sidebar with commit messages, timestamps, thumbnails
• Dependencies: Database persistence (Implement SQLite database layer with Drizzle ORM #10), canvas state serialization

References

• Original spec: docs/prd-v2.md P2+ (Version History)
• Canvas undo/redo: docs/roadmap/canvas-enhancements.md