perf: optimise autosave to only save on changes

[CodeWithBehnam]

Summary

• Add change detection to autosave to avoid redundant localStorage writes
• Use djb2 hash algorithm for fast, reliable change detection
• Skip autosave when workflow hasn't been modified

Technical Details

Before

Every 30 seconds, the autosave would:

1. Serialise the graph (CPU)
2. Strip large data (CPU)
3. Write to localStorage (I/O)

Even when nothing changed.

After

Every 30 seconds, the autosave now:

1. Serialise the graph (CPU)
2. Strip large data (CPU)
3. Hash the result (fast, O(n))
4. Compare with last hash (O(1))
5. Only write if changed (I/O only when needed)

Hash Algorithm

Uses djb2 (Daniel J. Bernstein) - a simple, fast hash function that's perfect for change detection. It produces a 32-bit unsigned integer from the JSON string.

function hashString(str: string): number {
  let hash = 5381
  for (let i = 0; i < str.length; i++) {
    hash = ((hash << 5) + hash) ^ str.charCodeAt(i)
  }
  return hash >>> 0
}

Test plan

• bun run typecheck passes
• bun run lint passes
• Autosave still works when changes are made
• No localStorage writes when workflow is unchanged

Behnam Ebrahimi