re(flight): axis probe pins the rows and checks liveness; fly_stage waits, not sleeps

Both fixes the previous run's caveats asked for, plus one the run itself forced.

axis_probe.py now:
 - PINS which non-forward row is up and which is right, by comparing world-Y
   across the rows in level flight, and says CONFIDENT or WEAK. entities2
   measures row 2 = forward against velocity, but the other two were labelled by
   the D3D convention, and yaw/pitch SWAP if that is wrong -- so the previous
   run's last two columns were named on an assumption.
 - checks the craft is ALIVE between inputs, and ABORTS with a message instead of
   reporting the clean zeros a destroyed craft produces. The first run ended on
   GAME OVER and only said so afterwards.
 - measures the UNKNOWN inputs (rx, ry, LB, RB) first while the craft is healthy,
   keeping the established lx/ly as controls at the end.

fly_stage.sh now WAITS for the stage load instead of sleeping a fixed guess. The
fixed sleeps worked until they didn't: one load ran long, the script pressed START
into a black screen, and every later step went to nothing while the screenshots
recorded a plausible-looking sequence. It now polls for a non-black frame and
aborts with a pointer to the log if the load hangs (PhysicalHeap::Release
failures) rather than continuing blind.

The probe itself did not run this iteration -- the stage load hung -- so there is
no new axis data, and none is claimed.

tools/re-capture/axis_probe.py

@@ -52,13 +52,16 @@ PAD_FILE = os.environ.get("XENIA_PAD_FILE", "/tmp/xenia_pad.txt")
 
 # Candidates. Sticks at full deflection, shoulders as buttons. Triggers are the
 # throttle (already settled) and are left out.
+# Order matters: the craft can be shot down mid-run, so the UNKNOWN inputs go
+# first while it is healthy and the already-established ones (lx = roll) go last
+# as controls. A row measured after death looks like a clean zero.
 CANDIDATES = [
-    ("lx+", {"lx": 32767}),
-    ("ly+", {"ly": 32767}),
     ("rx+", {"rx": 32767}),
     ("ry+", {"ry": 32767}),
     ("LB", {"press": "LB"}),
     ("RB", {"press": "RB"}),
+    ("lx+", {"lx": 32767}),
+    ("ly+", {"ly": 32767}),
 ]
 
 
@@ -84,6 +87,46 @@ def dot(a, b):
     return sum(a[i] * b[i] for i in range(3))
 
 
+def alive(w, off, cfg, secs=1.0):
+    """Is the craft still flying? A destroyed craft stops moving, and every
+    subsequent input then measures a clean, meaningless zero — the failure mode
+    that invalidated this probe's first run (it ended on GAME OVER and only said
+    so afterwards)."""
+    p0 = struct.unpack(">3f", os.pread(w.fd, 12, off))
+    time.sleep(secs)
+    p1 = struct.unpack(">3f", os.pread(w.fd, 12, off))
+    return math.dist(p0, p1) > 1.0
+
+
+def pin_rows(w, off, cfg):
+    """Which non-forward row is UP and which is RIGHT?
+
+    `entities2` measures row 2 = forward against the velocity vector, but the other
+    two are assigned by the D3D convention rather than evidence — and yaw and pitch
+    SWAP if that is wrong, so naming them without this test is a guess.
+
+    Discriminator: in level flight the craft's up-vector points along world +Y and
+    its right-vector lies near the horizontal plane. Sample at neutral and compare
+    |world-Y| across the rows."""
+    f_i = cfg["fwd_row"]
+    acc = [0.0, 0.0, 0.0]
+    n = 0
+    for _ in range(20):
+        time.sleep(0.05)
+        rs = rows_at(w.fd, off, cfg)
+        for r in range(3):
+            acc[r] += rs[r][1]          # world Y component
+        n += 1
+    ys = [a / n for a in acc]
+    cand = [r for r in (0, 1, 2) if r != f_i]
+    up_i = max(cand, key=lambda r: abs(ys[r]))
+    right_i = [r for r in cand if r != up_i][0]
+    print(f"# row world-Y means: {[round(y,3) for y in ys]}  (forward = row {f_i})")
+    print(f"#   -> up = row {up_i}, right = row {right_i}"
+          f"   {'CONFIDENT' if abs(ys[up_i]) - abs(ys[right_i]) > 0.3 else 'WEAK — craft may not be level'}")
+    return up_i, right_i
+
+
 def main():
     out_csv = sys.argv[1]
     dwell = float(sys.argv[2]) if len(sys.argv) > 2 else 5.0
@@ -93,7 +136,9 @@ def main():
         sys.exit("player entity not found")
     print(f"# locked on {nm}")
     f_i = cfg["fwd_row"]
-    u_i, w_i = [r for r in (0, 1, 2) if r != f_i]
+    if not alive(w, off, cfg):
+        sys.exit("craft is not moving at the start — not in flight, or already dead")
+    u_i, w_i = pin_rows(w, off, cfg)
 
     rows = []
     print(f"# {'input':<6} {'roll':>9} {'yaw':>9} {'pitch':>9}   (deg over the dwell)")
@@ -115,6 +160,10 @@ def main():
             prev = cur
         pad_state()
         wall = time.time() - t0
+        if not alive(w, off, cfg):
+            print(f"# CRAFT STOPPED MOVING after {label} — everything from here is "
+                  f"meaningless, aborting rather than reporting zeros")
+            break
         rate = [v / wall for v in sw]
         rows.append((label, *[round(v, 2) for v in rate]))
         print(f"# {label:<6} {rate[0]:9.1f} {rate[1]:9.1f} {rate[2]:9.1f}   deg/wall-s")