- keep editing an already-split transaction working when the flag is off:
only resend splits when the split content actually changed or was undone
- make the dashboard cashflow summary and the Transaction Analysis screen
split-aware (per-line category/type + tag attribution)
- skip split transactions on bulk label assignment (labels live on lines),
matching the existing bulk-category skip
- reject splitting a zero-amount transaction
- split editor no longer shows a green 'Remaining: 0' with a dead Save button
when a line is still zero
- add isSplit() helper, UUID split-line keys, clarify allocation docblocks
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