docs(test): note PR #107 for rain pass state sampling regression tests

Made-with: Cursor

Author: ap0ught

tests/rain-pass-state-sampling.test.mjs

@@ -7,6 +7,8 @@
  *
  * These tests lock in shader invariants as plain-text checks (no GPU). See also
  * tests/matrix-mathcode.spec.js for a browser smoke test.
+ *
+ * Introduced in PR #107 (rain pass state sampling fix).
  */
 
 import assert from "node:assert/strict";