wip(L25, side branch): FI helix enclosed in a 13 m rock root; support never created in open air

Fixes the L24 ribbon (owner request). NOT merged: the open-air support gate leaves ~4,000 unsupported
samples on every SurfaceWorld-recipe passage style (TN -> SW), a walkability regression. L26 fixes that
on this branch. See Linux25/REPORT.md.

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

ARCHITECTURE.md

@@ -1983,6 +1983,33 @@ cutaway views. Both affect captures only, not generated geometry.
 [`Standalone/Research/WorldAssemblerM3/Linux24/REPORT.md`](Standalone/Research/WorldAssemblerM3/Linux24/REPORT.md)
 records the evidence and owner-facing caveats.
 
+### 8.43 Enclosed FloatingIslands helix and native-solid passage support — World Assembler L25
+
+L24's support tread was composited into the passage field without requiring native solid terrain at
+the support sample. A 6 m root could not contain the resolved helix either: the centreline reaches
+5.562 m from the anchor axis and the mouth bore is 4.5 m. With the old root radius, the tread could
+therefore read as a free-floating spiral outside the rock. This was not a unit conversion error.
+
+The shared passage composer now emits route-mouth support, tread, and fallback support only where
+the pre-passage native density is solid. The open-air audit samples each support footprint at 0.25 m
+spacing and two depths, including route-mouth shelves; its L24 ungated-support control must report a
+violation. The FI anchor root is now a relief-bearing 13.25 m nominal rock column. Across five
+heights its measured radius is 12.0–13.375 m. Taking the maximum 5.562 m centreline radius and the
+full 4.5 m mouth bore at every height gives a conservative minimum wall of 1.938 m, exceeding the
+previous 1.5 m reserve. The authored mid-bore remains 3 m. The helix is selected from its route-bound
+root point and joins the lower route before the tunnel hands off through the shared SW ceiling.
+
+The configured FI Spiral passes the capsule/support/grade audit with zero blocked, unsupported, or
+grade-failure samples; the L23 smooth-wall control fails naturalness and the L24 ungated-support
+control fails the open-air audit. The other style overrides also pass the open-air audit, but their
+capsule results are recorded individually in the L25 report because some overrides are not
+walkable after floating support is suppressed. Evaluator version is 12, FI geometry version is 7,
+and resolved-layout schema V3 remains unchanged. The L25 report records measurements, hashes,
+captures, style results, and the single Unreal adapter version edit.
+
+[`Standalone/Research/WorldAssemblerM3/Linux25/REPORT.md`](Standalone/Research/WorldAssemblerM3/Linux25/REPORT.md)
+records the evidence and caveats.
+
 ## 9. Multiplayer model (listen-server first, dedicated-friendly)
 
 > **Status: transport is DESIGN ONLY — nothing is networked in-tree yet** (no `Replicated`/`HasAuthority`/RPCs; a