Source-aware editing

When Simba changes an existing document, the change is applied in a controlled, reviewable way. Rather than silently overwriting your work, edits to existing documents can be surfaced as a reviewable diff — additions and removals marked — that you accept in full, accept piece by piece, or undo.

This keeps a clear boundary between what you wrote and what the assistant proposed, and means AI assistance never puts your existing content beyond recovery.