diff --git a/developing-blockninja-plugins/SKILL.md b/developing-blockninja-plugins/SKILL.md
index 49d47a6..65a8fa0 100644
--- a/developing-blockninja-plugins/SKILL.md
+++ b/developing-blockninja-plugins/SKILL.md
@@ -166,6 +166,12 @@ marshaling to host functions. Full family/method table + disposition of every
 
 - `Interceptors`, `CoreServiceBindings` — **host-side**; RBAC method roles merge from the
   manifest, auth context arrives via forwarded HTTP headers (host interceptors already ran).
+- **Captcha is host-verified** (pluginsdk ≥ v0.2.2): a guest cannot hold the host's
+  stateful captcha server, so never import `block/core/captcha` (any core import/require
+  fails check-safety). Render the widget with the ninjatpl captcha tag; enforce with
+  `auth.CaptchaVerified(r.Header)` — the host consumes the posted `cap-token` and stamps
+  the unforgeable `X-Bn-Verified-Captcha` trusted header before dispatch. Fail closed
+  when it returns false. Reference: calcomblock `HandleCreateBooking`.
 - `AppURL`/`MediaPath` — delivered once in `LoadRequest.host_config`.
 - **`deps.Provisioner` (core ≥ v0.17.x) is the seeding path** — `EnsurePage`,
   `EnsureMenuItem`, `EnsureMedia`, `EnsureSetting`, `MergeSiteSettings`, data