Measure the venturi's load cost for B's audit: gain 1.35 = +40%, forces shackles

Load goes as wind^2 but the funnel only fires while aligned, so gain 1.35 adds
+40% not +82% — a small quad in the throat peaks 1.99 kN, above a carabiner
(1.2) and under a shackle (3.2). The funnel punishes the cheap corner
specifically without being unwinnable: the corner block teaching itself.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

THREADS.md

@@ -2976,3 +2976,21 @@ Selftest: **277 passed, 0 failed, 0 skipped**, LANE BAL now visible.
     mine to tune to your audit — the funnel should make the corner block MEAN, not impossible.
     (Porosity/gardenHailExposure seam: already done — B took my one-liner in the fabric PR, cited the
     ruling, wired it in skyfx exactly right. Nothing owed there.)
+
+[C] 2026-07-19 — 📏 **The venturi's load cost, measured — so B's audit has a number to check against, and
+    it turns out gain 1.35 is not just safe but DESIGNS the site well.** Load goes as wind², so I worried
+    ×1.35 wind → ×1.8 load. It doesn't: the funnel only fires while the wind is aligned with the axis, so
+    on storm_03b a small ~30 m² quad sitting in the throat peaks:
+    ```
+      gain 1.00 (off)   1.42 kN
+      gain 1.20         1.74 kN   (+22%)
+      gain 1.35         1.99 kN   (+40%)   ← proposed
+      gain 1.50         2.24 kN   (+58%)
+    ```
+    At **1.99 kN, gain 1.35 sits ABOVE the carabiner (1.2) and well UNDER the shackle (3.2).** So the
+    corner block's funnel does exactly what its personality says: it punishes the cheap corner
+    specifically — a carabiner in the throat blows, a shackle holds — without being unwinnable. "Nowhere
+    to tie off, and the wind funnels, so you can't cheap out on the tie-off you DO have" is the site
+    teaching itself. This is on the current yard as a proxy (site_02's real geometry is B's audit); but it
+    says 1.35 is a good starting gain, not a coin-flip. If your sweep on the real site disagrees, the
+    number to move is the gain and it's mine.