re: the mission script is resident immediately -- two explanations refuted

ssb_watch.py polls the .ssb header, a symbol string and find_mission from the
moment flight is detected. On a normal run all three are present at the FIRST
sample (t=0.0, mission 0xBC79C960), so 'the script loads later than assumed' and
'the probe raced a load' are both out -- there is no window in which a healthy
mission flies without its script in memory.

A detail worth more than it looks: at that sample screen_id reported 'other',
not 'flight'. The script is loaded and the ScriptMission locatable BEFORE the
flight HUD appears, so residency is not gated on the HUD, and a run showing the
HUD without the script is in a state a healthy run never passes through.

That leaves the third candidate: the anomalous run's mission never loaded and
its IN FLIGHT was a misdetection -- consistent with it being frozen on a black
screen when checked afterwards. Not proven, but now the only surviving
explanation rather than one of three.

tools/re-capture/ssb_watch.py

@@ -0,0 +1,63 @@
+#!/usr/bin/env python3
+"""When does the mission script become resident in guest memory?
+
+One run reached `IN FLIGHT` with the `.ssb` header ABSENT from guest memory and
+`find_mission` returning NOTFOUND, while the manifest string `Stage02.ssb` was
+present (script-runtime-probe.md). Three explanations were possible: the script
+loads later than assumed, the probe raced a load, or that run never really
+entered the mission.
+
+Sampling once cannot separate them. This polls from the moment flight is
+detected and records WHEN each marker appears:
+
+    header    the .ssb's 20-byte header  -> the script image itself
+    ADN110    a symbol-table string      -> its symbol table
+    mission   find_mission() succeeding  -> the live ScriptMission
+
+Usage: ssb_watch.py [secs] [every_s]
+"""
+import os
+import sys
+import time
+
+sys.path.insert(0, __file__.rsplit('/', 1)[0])
+import gmem
+import isl
+import squadron_state as S
+
+def main():
+    ssb = isl.load('/tmp/Stage02.ssb')
+    hdr = ssb[:20]
+    secs = float(sys.argv[1]) if len(sys.argv) > 1 else 300
+    every = float(sys.argv[2]) if len(sys.argv) > 2 else 10
+    path = gmem.mem_path()
+    size = os.path.getsize(path)
+    t0 = time.time()
+    seen = {}
+    with open(path, 'rb', buffering=0) as f:
+        while time.time() - t0 < secs:
+            t = time.time() - t0
+            marks = {}
+            marks['header'] = len(S._find(f, size, hdr))
+            marks['ADN110'] = len(S._find(f, size, b'ADN110'))
+            m, _fb = (None, None)
+            if marks['header']:
+                m, _fb = S.find_mission(f, size, ssb)
+            marks['mission'] = 1 if m else 0
+            for k, v in marks.items():
+                if v and k not in seen:
+                    seen[k] = t
+                    print('  [%6.1fs] %-8s FIRST SEEN (%s)' % (t, k, v), flush=True)
+            print('  [%6.1fs] header=%d ADN110=%d mission=%s' % (
+                t, marks['header'], marks['ADN110'],
+                ('0x%08X' % m) if m else 'no'), flush=True)
+            if len(seen) == 3:
+                print('all three resident at %.1fs' % t, flush=True)
+                return 0
+            time.sleep(every)
+    print('timed out; seen=%s' % seen, flush=True)
+    return 1
+
+
+if __name__ == '__main__':
+    sys.exit(main())