Docs: session log Part N — flora double-animation diagnosis + thinning

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Docs/Vault/07_Sessions/2026/2026-07-09_B4d_Tail_Collision_Grounding.md

@@ -289,6 +289,21 @@ teardown proven (run abort → 0 children); Meadow ground tint converged to the
 470/470 EditMode; console clean. Edit-mode renders: base reads as a living meadow with a worn path to the
 warpgate.
 
+## Part N — flora feel fix (`9670465e2`): the double-animation diagnosis
+
+Operator lap on the ground bundle: flowers too dense + "the waving/shader doesn't look great, not sure what
+to change." Diagnosis: **every Synty flora prop in BOTH biomes runs the `Synty/Foliage` VERTEX-wind shader**
+(light+strong wind, twist, gale-bend all enabled at authored defaults) — the AmbientMotionSystem root-tilt
+sway has been double-animating all flora since it shipped, and the newly enabled ground-flush carpets
+(`Flowers_Flat`, `Grass_*_Plane`) lift their edges off the ground on ANY root rotation. ★ Lesson: before
+transform-animating "static" art, check the shader — Synty foliage is never static.
+
+Fix: `SwayEnabled=false` (code default + the serialized scene value — the ★ serialized-beats-initializer
+gotcha again); the shader wind IS the idle motion, walk-through rustle stays as the reactive layer; flat
+carpets excluded from the flora cache entirely; flower drifts thinned deterministically (Flat 40% /
+Wildflower+Sunflower 50%, center r<13 ×0.6 → 17/38 off) so the play/build area reads clear and flowers
+become ring accents.
+
 ## Next-session intent
 
 **Phase 1.5b bundle 1 (ground) is SHIPPED**; remaining locked bundles in order: **2) decals** (explosion