HubCamera.gd follow-distance fix — instrumented walkthrough (real gameplay
follow camera, scripted player walking north through the ON AIR doorway).

Before the fix, SpringArm3D's own built-in collision response snapped
spring_length to the raycast hit distance within a single physics frame.
The invisible camera-only threshold plate at the doorway sits where the
player themselves walks through, so the instant they crossed it the
follow distance fell from ~3.4m to near-0m in one frame, then crawled
back out over the next few meters -- reads exactly like hitting an
invisible wall even though movement itself was never blocked.

After the fix (manual raycast + asymmetric lerp: fast pull-in near a
wall, slower release), the same walkthrough shows a smooth dip and
recovery instead of a snap:

walkthrough frame=6  player_z=10.38 arm_len=1.67
walkthrough frame=12 player_z=9.07  arm_len=0.86   <- tightest point, at the threshold
walkthrough frame=18 player_z=7.60  arm_len=1.73
walkthrough frame=24 player_z=6.14  arm_len=3.04   <- back to normal follow distance

Verified via godot --path . --rendering-driver opengl3 (llvmpipe software
rendering), Tool_HubScreenshot.tscn with an added diagnostic walkthrough
pass (not committed to the tool script -- reverted after use).