Rider not receiving orders when switching status from "Unavailable" to "Available" during the unassigned order period.

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Describe the bug
When a rider switches their status from "Unavailable" to "Available" during the time window in which an order has not yet been assigned to any other rider, the system fails to assign the order to the rider. This behavior creates a situation where the rider misses out on receiving available orders even though they are now available to take them.

To Reproduce

A rider is in "Unavailable" status.
An order is placed in the system but has not yet been assigned to any rider.
The rider switches their status to "Available."
The rider does not receive the order, despite the order still being unassigned.
Expected behavior
When a rider changes their status from "Unavailable" to "Available," they should immediately be eligible to receive any unassigned orders. If there is an unassigned order available during this transition, the system should assign it to the rider.

Actual Result
The rider remains unassigned to the order, and no notification or assignment occurs for that order, even though it was unassigned and the rider is available.

Smartphone (please complete the following information):

Device: iPhone15pro
OS: iOS17.6.1

Start by reproducing the rider status transition while an order remains unassigned, then trace the status-change and order-assignment flow. Confirm how availability changes are handled and verify that an available rider receives an eligible unassigned order immediately after switching from Unavailable to Available.

Written by the indexing model from the issue text.