Record why the probe has no entry function

docs/decisions.md

@@ -688,7 +688,8 @@ though `hasRead` states the same stop rule. Valid while the two differ in where
 
 2026-09-28, larv-review on systems-architect's finding; awaiting approval. Goals 2 and
 11: `pathCheck`, `pathCover`, `pathProbe` and `pathDraw` each loop over `stepInto` and
-`table.route` themselves. One walk calling them through an interface or a type parameter
+`table.route` themselves, and `descend` and `tableReadOf` build their probe in place, so
+its `drawn` map stays on the stack. One walk calling them through an interface or a type parameter
 leaks the walker and the pins it holds, an allocation per reference read. Valid while Go's
 escape analysis treats a call through an interface or a type parameter as leaking its
 receiver.