Dumping Jobs Not Respecting Export Priority Setting On Storage

Issue description

Dumping jobs do not seem to respect the priority number assigned to the storage the items are being exported from.

For example, I have several mines that have storage buildings nearby for the mining trucks to store excess rock and dirt. The storage assigned to the mine then feeds into another storage which is set to export, with a priority between 12 and 15 (depending on the mine). A large percentage of my trucks are exporting and dumping from these low-priority storage buildings, even when there are many other jobs available with higher priorities going unfilled.

It appears that dumping jobs have an implicit priority of 9 or 10, regardless of the priority set to storage being exported from.

Expected behavior

I would have expected storages with export priorities of 15 would be the last jobs to be filled, only when there are no other higher priority jobs available on the island.

Reproduction steps

1. Make sure there are plenty of non-dumping jobs available with priority 10 or 11 (enough to require all trucks to be busy doing them).
2. Fill a storage with rock or dirt.
3. Set export on rock/dirt storage, and set it to export priority 15
4. Observe that trucks will start emptying that storage, even though higher priority jobs are available.

Game version

v0.4.10

Attachments

Dumping Priority Issue.save

Files not imported: Dumping Priority Issue.save

I have had this issue with waste versus rock or dirt storage.
Waste storage container with priority 1 set is ignored while rock and dirt containers with priority 15 set.
All available trucks go to the priority 15 containers and start dumping. Which means there are no available trucks to service the rest of the Island. (Waste storage with priority 1 is ignored.)

I think the answer would be to only allow a certain percentage of available trucks to dump the lower priority storages. Trucks available would be allocated based by priority. And maybe a certain percentage of the trucks would be left alone and not allocated to moving items to/from storage units.

So maybe 20 to 50 percent (of available trucks) would be left alone for high priority stuff and as a general buffer (pool). Letting us set the number of trucks that are left in the general pool in settings would help us in figuring out what percentage works best.

The remaining trucks in the pool would be allocated to the storage units based on priority.

Duplicate of Trucks ignoring P2 export request