wip(assembler): round L18 -- FloatingIslands false floors removed; shared strate ceiling

FI geometry v3 drops the all-XY lower boundary seal that created false floors (3.5/8 m); the
ceiling comes from the shared VF_ApplyUpperBoundarySeal and AppendStratumBoundaryCeilings path
for every generator, at each strate's own configured upper boundary (owner: every strate has a
ceiling). Far-LOD ceiling continuity: 0 gaps at LOD4-8. SurfaceWorld bit-identical to L14
(14 configs + 24 m crossing); FI deterministic (28-row matrix); route parity and proofs pass.
Unreal: FI geometryVersion 2->3 and the shared upper-seal helper extracted (UBT compile needed on
the owner PC). Open: small ceiling holes; lower-stratum LOD ring steps seen through the FI void.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CSFYgsdW8ejZSyiMf4qRSX

Standalone/Research/WorldAssemblerM3/Linux18/CheckSurfaceHashes.py

@@ -0,0 +1,25 @@
+#!/usr/bin/env python3
+"""Compare every L18 SurfaceWorld matrix hash row with the approved L14 reference."""
+import re
+import sys
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[4]
+RUNS = ROOT / "Saved/Linux/l18-matrix"
+REFERENCE = ROOT / "Saved/Linux/l14-final-hash-sw-clang-off-w12-r5.log"
+PATTERN = re.compile(r"^\[Pipeline(?:FullDetailHash|WholeViewHash|LODHash|ExactQueryHash)\].*$", re.M)
+expected = PATTERN.findall(REFERENCE.read_text(encoding="utf-8"))
+if not expected or len(expected) != 12:
+    raise SystemExit(f"invalid L14 reference hash rows: {len(expected)}")
+logs = sorted(RUNS.glob("surface-world-*.log"))
+if len(logs) != 14:
+    raise SystemExit(f"expected 14 SurfaceWorld matrix logs, found {len(logs)}")
+failed = []
+for path in logs:
+    actual = PATTERN.findall(path.read_text(encoding="utf-8", errors="replace"))
+    if actual != expected:
+        failed.append(path.name)
+        print(f"[SurfaceHashMismatch] {path.name} expected={len(expected)} actual={len(actual)}")
+print(f"[SurfaceHashGate] reference={REFERENCE.name} rows={len(logs)} expected_rows=14 "
+      f"result={'FAIL' if failed else 'PASS'}")
+raise SystemExit(1 if failed else 0)