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/MeasureBuild.py

@@ -0,0 +1,67 @@
+#!/usr/bin/env python3
+"""Measure peak per-process RSS for a build process tree under the L17 limits."""
+import os
+import subprocess
+import sys
+import time
+from pathlib import Path
+
+
+def descendants(root):
+    pending = [root]
+    seen = set()
+    while pending:
+        pid = pending.pop()
+        if pid in seen:
+            continue
+        seen.add(pid)
+        try:
+            children = Path(f"/proc/{pid}/task/{pid}/children").read_text().split()
+            pending.extend(int(child) for child in children)
+        except (FileNotFoundError, PermissionError, ProcessLookupError):
+            pass
+    return seen
+
+
+def status(pid):
+    try:
+        fields = {}
+        for line in Path(f"/proc/{pid}/status").read_text().splitlines():
+            if line.startswith(("Name:", "VmRSS:", "VmSize:")):
+                key, *value = line.split()
+                fields[key[:-1]] = value[0] if value else ""
+        return (int(fields.get("VmRSS", "0")), int(fields.get("VmSize", "0")),
+                fields.get("Name", ""))
+    except (FileNotFoundError, PermissionError, ProcessLookupError, ValueError):
+        return None
+
+
+if len(sys.argv) < 2:
+    raise SystemExit("usage: MeasureBuild.py command [arguments ...]")
+if not os.sched_getaffinity(0).issubset(set(range(12))):
+    raise SystemExit("run under taskset -c 0-11")
+
+started = time.monotonic()
+process = subprocess.Popen(sys.argv[1:], start_new_session=True)
+peak_rss = (0, 0, "")
+peak_vms = (0, 0, "")
+while process.poll() is None:
+    for pid in descendants(process.pid):
+        measured = status(pid)
+        if measured is None:
+            continue
+        rss, vms, name = measured
+        if rss > peak_rss[0]:
+            peak_rss = (rss, pid, name)
+        if vms > peak_vms[0]:
+            peak_vms = (vms, pid, name)
+    time.sleep(0.1)
+
+exit_code = process.wait()
+elapsed = time.monotonic() - started
+print(f"[BuildTreeResources] exit_code={exit_code} wall_s={elapsed:.3f} "
+      f"peak_process_rss_kib={peak_rss[0]} peak_rss_pid={peak_rss[1]} "
+      f"peak_rss_name={peak_rss[2]} peak_process_vms_kib={peak_vms[0]} "
+      f"peak_vms_pid={peak_vms[1]} peak_vms_name={peak_vms[2]} "
+      "monitor_interval_s=0.1", flush=True)
+raise SystemExit(exit_code)