When an order changes driver

Before every assignment attempt, the dispatcher checks whether an order already assigned to one driver should instead go to a different one — but only on driver priority, never on how urgent or important the order itself is.
When a reassignment is allowed
Situation
Result
Order has no driver yet
Assign freely
Previously assigned driver is no longer available
Assign freely
Same driver being considered again
No change needed
New driver has better priority
Reassign
Current driver has equal or better priority
Keep as-is
Priority is defined in Driver classification and priority.
Common scenarios
Current driver
Candidate driver
Outcome
External driver
Internal driver
Reassigned — better type
Idle, at store
Idle, at store
No change — both equally good
Idle, away from store
Idle, at store
Reassigned — better location
Waiting, at store
Idle, away from store
No change — current is still better
External, away from store
External, away from store
No change — no real improvement
Passing the priority check is not a delivery guarantee
Passing it only means the dispatcher will attempt the assignment. It still has to verify the new driver can actually deliver on time:
Driver situation
Delivery time checked?
Idle, at store
No — always the fastest possible option
Idle, away from store
Yes
Waiting (already has orders)
Yes — must be able to deliver everything
On The Way
Yes — the full route is recalculated
If the delivery-time check fails, the assignment is reverted and the order stays available for the next driver in line. It isn't lost.
Rules that never change
Orders already out for delivery — the driver has left the store — are never reassigned.
Manually assigned orders, assigned by an employee rather than the dispatcher, are completely locked from automatic reassignment.
Internal drivers can take an order away from an external driver. The reverse is never allowed.