diff --git a/AGENTS.md b/AGENTS.md
index d9034f5c2136815d3bfdfe2a8982a446dc43f5df..0df6c971efb908945d9e557309c91627fae95ad5 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -38,6 +38,15 @@ Two categories of skills exist:
 - **Generic capability skills** (`formatting-commits`): Use specific tools to accomplish general tasks. Tool name omitted from skill name.
 - **Service workflow skills** (`creating-tasks-through-lunatask`): Workflows for specific proprietary services. Service name included via `-through-{service}` suffix.
 
+## Vendored Skills
+
+Some skills under `skills/` are symlinks into `vendor/`. These come from external repos via `git subtree --squash`. Don't edit them directly — changes will be overwritten on the next pull.
+
+- **Manifest**: `vendor/sources` lists each vendored repo (tab-separated: name, URL, branch)
+- **Update all**: `scripts/vendor-update.fish`
+- **Update one**: `scripts/vendor-update.fish REPONAME`
+- **Add a new vendor**: `git subtree add --prefix=vendor/REPONAME URL BRANCH --squash`, add a line to `vendor/sources`, symlink desired skill directories into `skills/`
+
 ## Design Principles
 
 1. Progressive disclosure: Frontmatter loads at startup; SKILL.md body loads on activation; references/ load on-demand