passages: smoothed open-air shell joins (L110, v257) - partial, not merged

Bands = end profiles of per-control-span shell capsules (~9.35 m pitch = span spacing).
Shell now smooth-unions adjacent spans over 6 m and reuses the interior chord distance; a 0.60 m
clearance fades in 5-20 m from each mouth. Close-ups: bands reduced but still visible on part of
the exposed shell. Cost vs L109: near-ready +8..+12% (FI 0.88 -> 1.00, TN 0.92 -> 1.01 s @W12).
Audits, Clang/GCC determinism, fast tier and Linux UE build pass. Kept on its own branch.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Standalone/Research/WorldAssemblerM3/Linux110/captures/capture-verification.json

@@ -0,0 +1,30 @@
+{
+  "status": "PASS",
+  "capture_count": 106,
+  "open_air_sections": 9,
+  "per_variant_kind_counts": {
+    "before": {
+      "mouth": 6,
+      "open-air": 27,
+      "open-air-closeup": 11,
+      "station": 9
+    },
+    "after": {
+      "mouth": 6,
+      "open-air": 27,
+      "open-air-closeup": 11,
+      "station": 9
+    }
+  },
+  "paired_image_bytes": {
+    "mouth_changed": 4,
+    "mouth_identical": 2,
+    "open-air-closeup_changed": 10,
+    "open-air-closeup_identical": 1,
+    "open-air_changed": 24,
+    "open-air_identical": 3,
+    "station_changed": 1,
+    "station_identical": 8
+  },
+  "errors": []
+}