test(camera): -cameratest harness for the spring-arm collision, result inconclusive

0.2.3 is about camera clipping, and nothing had ever exercised the spring arm's
collision test. This adds a harness: find the nearest wall from the spawn, stand the pawn
70 cm off it facing away, wait for the boom, then report the arm length, whether the boom
ends inside geometry, and a back-trace from camera to head.

Inconclusive, and the setup is the suspect rather than the engine: every run reports the
arm at its resting 340 cm, but BOTH traces come back clear, so nothing was between the
pawn and the boom at all. The placement is wrong, not necessarily the collision.

Three wrong turns recorded in TODO.md because each cost a run: the probe accepted the
floor as a wall, then faced the pawn into the wall by negating the impact normal (which
points away from it), then set actor rotation only - which a possessed pawn discards in
favour of control rotation.

Next: look at the placement screenshot before trusting the measurement.

TODO.md

@@ -11,9 +11,13 @@ Actionable task list for this project. This file is the single, central place fo
 
 ## 0.2.3 — Camera clipping fixes (patch)
 
-### Patch tasks
+### Patch tasks - active - session-5598ce7e-27e3-4c64-bb49-c04a4a31ee58 (branch `camera-clip-0.2.3`)
 
-- [ ] Fix remaining camera clipping cases in `0.2.x`.
+- [A] Fix remaining camera clipping cases in `0.2.x`. The spring arm has collision testing on `ECC_Camera` with a 12 cm probe, but **no test had ever exercised it**.
+  - **Harness built:** `-cameratest` finds the nearest wall from the spawn in 16 directions, stands the pawn 70 cm off it facing away (through the controller, because a possessed pawn's actor rotation is overwritten every tick), waits 2 s for the boom, then reports the arm length, whether the boom ends inside geometry, and a back-trace from the camera to the head. It also requests a screenshot so the placement can be checked by eye.
+  - **Inconclusive so far, and the setup is the suspect, not the engine.** Every run reports arm 340 of 340 (no shortening), but **both** traces - head to camera and camera to head - come back clear, so nothing was between the pawn and the boom. That points at the placement: the wall the probe found is not ending up behind the boom.
+  - **Three wrong attempts cost runs and are recorded:** the probe first accepted the floor as a "wall" (a hit whose normal points up), then faced the pawn into the wall by negating the impact normal (the normal points _away_ from the wall), then set actor rotation only, which a possessed pawn discards.
+  - **Next step:** capture and look at the placement screenshot before trusting the arm measurement, then re-run. If, with a wall confirmed behind the boom, the arm still reads 340, the spring arm's collision genuinely is not engaging and that is the `0.2.3` fix.
 - [ ] Tag `v0.2.3` and write `CHANGELOG.md` entry; then remove this section.
 
 ## 0.3.0 — Chaos vehicle, enter/exit, closed driving route (weeks 10–13)