diff --git a/skills/freebsd-os-upgrade/SKILL.md b/skills/freebsd-os-upgrade/SKILL.md
index 3011e63..2e0f2d1 100644
--- a/skills/freebsd-os-upgrade/SKILL.md
+++ b/skills/freebsd-os-upgrade/SKILL.md
@@ -112,8 +112,13 @@ tolerated, but move them up for consistency + security). OSA uses **Bastille**
 - **Thin jail** — a clone/overlay of a bootstrapped release template. Bootstrap
   the new release once, then bring each thin jail up off it.
 
-Each jail's base is managed the same two ways as the host — detect per jail:
-`bastille cmd <jail> pkg info -e FreeBSD-runtime` (pkgbase) vs freebsd-update.
+Each jail's base is managed pkgbase or freebsd-update. For a **thick** jail
+(independent base) detect it directly:
+`bastille cmd <jail> pkg info -e FreeBSD-runtime` (present = pkgbase). On a
+**thin** jail this may be empty or error — a thin jail has no independent
+pkg-managed base; its method follows the release **template** it was bootstrapped
+from, and you upgrade it at the template level (re-bootstrap / re-clone or
+`bastille upgrade`), not per-jail.
 
 Bastille flow (confirm against the installed Bastille version + bootstrap method):