NPC's have difficulty moving through the Freshwater Research Station

Describe the bug

NPC's act strangely when attempting to move through the Freshwater Research Station.

Steps To Reproduce

1. Make a character with the Safe Place start at a Freshwater Research Station
2. Spawn an NPC and make them a follower
3. Attempt to bring them into the lower levels
4. Watch as they get stuck on the door or somehow end up at the bottom level (z level -4) by the submerged entrance stuck outside.

If you force the NPC through the door, they also have trouble actually moving up and down the ladders. Sometimes not moving at all. Other times following you up only to the surface after a few minutes of waiting but not following you back down again or to any other levels.

Expected behavior

NPC's to be able to actually traverse the doors and ladders in this location and not just open them and stand there.

Versions and configuration

• OS: Windows
  • OS Version: 10.0 1909
• Game Version: 0.E-8626-g6b09767 [64-bit]
• Graphics Version: Tiles
• Game Language: System language []
• Mods loaded: [
  Dark Days Ahead [dda]
  ]

Additional context

NPC's also seem to be able to traverse up and down through the water z-levels in an attempt to follow you down if they're not stuck inside. They also occasionally end up outside after being stuck inside and will be waiting on the surface for you.

Changing the doors to a different door lets the NPC move through them but changing the ladders out for stairs doesn't.

The (t_bulkhead_floor) terrain used in the lower levels also has a 400 move cost for some reason making it take 4 seconds to move across one tile. The entrance just uses normal metal floors with a 100 move cost instead.

Partly related to #46124 .

Start by reproducing the follower's movement through the Freshwater Research Station, especially its doors, ladders, and submerged entrance. Check the NPC traversal behavior alongside the t_bulkhead_floor movement cost; done means followers can reliably move between all station levels without getting stuck or taking unintended routes.