S18 integration: keep the session fallback on the fabric seam — SHADES.rigSail is a third caller neither lane enumerated (A: revert on sight if you disagree)

web/world/js/main.js

@@ -871,8 +871,16 @@ export async function boot(opts = {}) {
    *    still flies the membrane". A fix that waits for a merge to start working is
    *    not a fix yet. `session.fabric` is the expression this file already reads
    *    for the paperwork, so the physics and the invoice now read ONE source.
-   * When B's rigging.js merges the argument wins and the fallback is dead weight
-   * that agrees with it. Delete the fallback then, not before.
+   * **AT INTEGRATION (S18, integrator): B's rigging.js is merged, the argument
+   * now arrives on both wired routes — and the fallback STAYS.** A's filed
+   * instruction was to delete it here; it is deliberately not deleted, and A can
+   * revert this on sight. The reason is a third caller neither lane enumerated:
+   * `rigSail` is exposed on the `SHADES` API, where a bench or a cold play can
+   * still call it with three arguments. Deleting the fallback would make that
+   * path fly the membrane while every card said cloth — the exact five-sprint bug
+   * this fix exists to kill, reintroduced through the one door the suite cannot
+   * see (this wire lives inside `boot()` behind a WebGL context). The fallback is
+   * one `??` and it agrees with the argument on every wired path.
    */
   async function rigSail(anchorIds, hwChoices, tension = 1.0, fabric) {
     const cloth = fabric ?? rigging?.session?.fabric;