Fix: recompute sun-frame trail and SOI crossings after flyby

After SOI exit the asteroid has new orbital elements (gravity assist).
Previously the old trail and crossing predictions were never updated,
causing three bugs:
  1. Old trajectory still drawn after exit
  2. Next SOI entry time based on stale orbit
  3. Subsequent SOI entries never triggered

Now on exit: recompute trail, rescans for future SOI crossings,
and resets the crossing index.

visual_test.py

@@ -247,15 +247,24 @@ def main() -> None:
             asteroid_planet = None
             soi_exit_time = None
 
-            # Advance to next crossing
+            # ── Recompute trail from new sun orbit ──────
-            cross_idx += 1
+            trail_asteroid_sun = [
-            while cross_idx < len(sun_crossings):
+                to_screen(x, y) for x, y in
-                if sun_crossings[cross_idx][0] > sim_time + 0.1:
+                generate_orbit_points(asteroid_sun)
-                    soi_enter_time = sun_crossings[cross_idx][0]
+            ]
-                    break
+
-                cross_idx += 1
+            # ── Recompute future SOI crossings ───────────
-            else:
+            window = SEARCH_ORBITS * max(asteroid_sun.period, PLANET.period)
-                soi_enter_time = None
+            sun_crossings = find_soi_crossings(
+                asteroid_sun, PLANET, SOI_RADIUS,
+                sim_time + 0.1, sim_time + window, n_steps=1000,
+            )
+            print(f"    Re-scanned: found {len(sun_crossings)} future crossing(s)")
+            for i, (enter, _) in enumerate(sun_crossings):
+                print(f"      [{i}] enter={enter:.1f}s")
+
+            cross_idx = 0
+            soi_enter_time = sun_crossings[0][0] if sun_crossings else None
 
         # ── Compute current positions ──────────────────────
         px, py = PLANET.position_at(sim_time)