re-capture: a dead display must not look like a playing movie

skip_intro.sh compared two screenshots to detect the intro movie. When the X
server died 3 min into a run, `screenshot` failed silently and left both PNGs
at their previous contents — two stale files, whose RMSE is a constant non-zero
number, i.e. exactly the signature of a changing screen. The loop then reported
"movie -> skip A" every 5 s for the whole 600 s timeout with no emulator and no
display alive, and the session wasted 10 minutes before saying BOOT FAILED.

Both waiters now verify, every iteration, that the screenshot was actually
written, that the display answers xdpyinfo, and that a non-zombie xenia_canary
exists — with distinct exit codes (3 display, 4 emulator, 5 capture) so the
session log names the cause instead of timing out.

Also adds mission_state.py + escort_session.sh: read pos+0x154 against each
definition's HP for EVERY entity, to test whether the hull anchor is a property
of the entity class rather than of the player object (the escort question).

tools/re-capture/launch_mission.sh

@@ -35,7 +35,7 @@ cd /sylph-home/re
 setsid nohup run-canary --audio --apu=sdl --log_mask=13 \
   --logged_profile_slot_0_xuid=E0300000EFBEA3D4 </dev/null >/dev/null 2>&1 &
 sleep 5
-"$SD/skip_intro.sh" 600 || { echo "BOOT FAILED"; exit 1; }
+"$SD/skip_intro.sh" 600 || { echo "BOOT FAILED (skip_intro exit $?)"; exit 1; }
 sleep 14                       # main menu is not input-ready before this
 
 step down                      # NEW GAME -> LOAD GAME